4th U.S. National Climate Assessment Vol. II: Notable Findings

NCA4, Part Two: Impacts, Risks and Adaptation

How Climate Change is harming humanity, shaping societies and endangering environments

The Trump Administration’s recently published 4th National Climate Assessment Volume II, on climate impacts, risks and adaptation covers 19 national topics and ten regions, summarizing the vast body of scientific literature on how climate change is already causing problems for Americans. It was drafted by over 300 leading scientists, who conducted regional workshops in over 40 cities with over 1,000 people.

The effort was led by NOAA, but with a steering committee of representatives from the 13 federal agencies comprising the US Global Change Research Program (USGCRP, a presidential initiative started by Ronald Reagan and signed into law in 1990.)

Here is a selection of findings from each chapter, for an even shorter version see our Main Messages page.

Chapter 1: NCA4 Overview

  • Climate change is already causing problems to which Americans are already responding, from flooding in the coast, to pests in the heartland, fires out west, thawing permafrost in Alaska, and more.
  • Human activities are causing the climate to change faster than it has at any point in this history of modern civilization.
  • Evidence of human causation is undeniable and growing. We’re not doing enough yet, but taking further action will reduce those threats.
  • Climate change is already a threat to American health and wealth, as high summer temperatures increase the risk of illness and death and the heat wave season has already increased in by over 40 days since the 1960s in some cities.  
  • The warming in high emissions scenario is expected to cost $160 billion in lost wages; 2 billion labor hours lost annually by 2090 due to temperature extremes.
  • The most vulnerable populations face the highest risk as lower-income and marginalized communities face additional barriers for coping with extreme weather and other climate-related events.
  • Sea level rise is already forcing people to abandon coastal communities, and a wider coastal retreat will be “unavoidable” in some areas in all but the most optimistic sea level rise expectations.
  • Climate change is already making some extreme weather more common and more intense. Climate change links have been found in heat waves, droughts, fires, floods, storms and hurricanes.
  • Climate change already impacting biodiversity, causing large-scale shifts in species and altering ecosystems, but aiding in the spread of invasive species.

Chapter 2: “Our Changing Climate”

  • This chapter is drawn from NCA4 Volume 1; see our Notable Findings on it here.
  • Global average temperature increased by about 1.8F/1C between 1901 and 2016, 1.2F of which has been since 1986. Human activities are the dominant cause. Greenhouse gasses cause climate change. The climate we are headed for will be 9F(5C) warmer by 2100, but if we transition off of fossil fuels quickly enough, we can keep it limited to 3.6F (2C.). If we don’t, we could be as much as 12F warmer by 2100.  Regardless, our emissions this century will leave a legacy in the climate system that will last over 10,000 years.
  • Observed warming from 1951-2010 was 1.2F/.65C, with the likely range of human contribution being between 1.1F and 1.4F (.6C to .8C). This means that at a minimum, 1.1 of the 1.2F warming since 1951 was caused by human activity, like burning fossil fuels. But how is it likely that humans contributed 1.4 degrees of warming if we’ve only seen a 1.2 degree increase? Because naturally, the climate would be slightly cooling. But greenhouse gasses are overwhelming the natural factors that would have us experiencing slightly below average temperatures, and instead pushing us to record highs.
  • Oceans have absorbed 93% of warming, and a quarter of the CO2. That’s causing our oceans to acidify. Carbon pollution, combined with rain, wind, nutrient changes and ocean circulations, are already reducing in oxygen levels in many locations.
  • There has been 7-8 inches of sea level rise since 1900 (almost half, 3 inches, since 1993), and there will be several more inches in next 15 years. Sea level rise has made high tide flooding five to 10 times more frequent for some coastal communities since the 1960s. Frequency, depth and extent of tidal flooding will increase, particularly with more severe flooding from coastal storms.
  • In the 20th century, sea levels rose at a rate unseen in at least 2,800 years.
  • We are on a path to oceans one to four feet higher by the end of the century, and one foot of sea level rise would be enough to raise high tide floods to catastrophic levels.
  • If Antarctica hits a tipping point and melts, which is physically possible, we could see 8 feet of sea level rise under low and high emission scenarios.
  • Paleoclimate records suggest that warming already recorded could lead to as much as 20 feet of sea level rise over the long term, while the 3.6°F (2°C) Paris agreement target would lead to about 80 feet of warming over 10,000 years. A high emission scenario would represent a 10,000 year commitment of 125 feet of sea level rise.
  • Heat waves have become more frequent since the 1960s, as cold waves has gotten more rare. Record highs are growing far more common than record low temperatures, and the frost-free seasons has grown.
  • Climate change has made heavy rainfall events more frequent and intense, a trend that’s expected to continue. Rainfall levels are climbing in the northern and eastern parts of the United States, but down across the south and west. These trends are also expected to continue.
  • As more rain falls as rain and less as snow as a result of global warming, soil moisture and snowpack trends are expected to continue the already observed declining trend.
  • Human activities like burning fossil fuels have warmed the Arctic, and melted sea ice and glaciers. Arctic temperatures are increasing twice as fast as the global average and by mid-century we will very likely see a nearly ice-free arctic in late summer, the first time this will have happened in about 2 million years. Sea ice extent is already decreasing by 3.5%-4.1% per decade, and its minimum extent when melted in the summer is shrinking 11%-16% per decade.
  • The ice melt season has already lengthened by at least five days per decade since 1979, making it almost three weeks longer.  September sea ice has decreased at a rate of about 13% a year between 1979 and 2016.
  • Greenhouse gases have played an role in the increased in Atlantic hurricane activity since 1970, and Atlantic and eastern North Pacific hurricane rainfall and intensity are projected to increase, as is frequency and severity of atmospheric rivers on the West Coast. The total number of storms expected to remain constant or decrease, but intense storms will become more frequent and drop more rain.
  • Climate change impacts like warmer waters and higher sea levels made record-breaking Hurricanes Harvey, Irma, Jose and Maria worse through greater rainfall and higher sea levels, and the rapidly intensifying storms of 2017’s Atlantic hurricane season is a preview of climate impacts to come.
  • Carbon dioxide levels are now higher than any time in the last 3 million years, when temperatures and sea levels were much higher. The current emissions rate of nearly 10 gigatons of carbon per year is unprecedented in at least the last 50 million years. Put another way, we’re emitting at a rate unseen in at least 50 million years, and continued grown in emissions would create conditions not seen on this planet for tens to hundreds of millions of years.

Chapter 3: Water

  • Significant changes in water quantity and quality are evident across the country.
  • Warming is reducing snow-to-rain ratios, leading to significant differences between the timing of water supply and demand.
  • Groundwater depletion is exacerbating drought risk.
  • Surface water quality is declining as water temperature increases, and more frequent high-intensity rainfall events muddy waters.
  • Deteriorating water infrastructure compounds the climate risk faced by society. Extreme rain events are projected to increase in a warming climate, leading to more severe floods and greater risk of infrastructure failure in some regions.
  • Climate change not generally incorporated into infrastructure design, operation, financing principles, and regulatory standards, putting our infrastructure at risk.
  • Water systems already face considerable risk, even without anticipated future changes.
  • Dams and levees already in poor condition will be at an even greater risk as extreme rain events become more common and intense.
  • Warmer water increases the risk of harmful algal blooms, especially when combined with greater fertilizer runoff that results from extreme rainfall.

Chapter 4: Energy Supply, Delivery, and Demand

  • The U.S. energy system, which underpins nearly every sector of the US economy, is increasingly impacted by extreme weather events, which are becoming more frequent and severe with climate change.
  • Extreme weather is the leading cause of power outages in the U.S.
  • There are 291 electricity generation facilities in the Southeast potentially exposed to a Category 5 hurricane storm surge
  • Increase in baseline sea level exposes many more Gulf Coast refineries to flooding risk. For a Category 1 hurricane, a sea level rise of less than 1.6 feet doubles the number of refineries in Texas and Louisiana vulnerable to flooding.
  • Rising temperatures and extreme heat waves lead to increased demand for cooling, which can increase energy-related air pollution, lead to blackouts, and potentially increase electricity prices for consumers.
  • If greenhouse gas emissions continue, it could cost residential and commercial ratepayers up to $30 billion per year by mid-century.
  • Changes in the energy mix are also changing the system’s vulnerabilities to climate and extreme weather.
  • Solar and wind generation grew by 44% and 19% in 2016, respectively
  • Actions are already underway to help protect the energy system from climate change and extreme weather impacts. Opportunities exist to accelerate the pace, scale and scope of these actions.  After Hurricane Sandy caused 8.7 million households to lose power, utility companies in New York and New Jersey spent billions on upgrades to reduce the risk of future outages.
  • Energy efficiency and other programs are improving grid reliability without increasing power generation.
  • Distributed generation sources such as solar, fuel cells, energy storage, and microgrids help protect energy systems from extreme weather hazards and keep critical services running during potential power outages.

Chapter 5: Land Cover and Land Use Change

  • Changes in land use can be due to climate drivers and human drivers – policy, economics, and technology – and are increasingly influenced by market globalization.
  • If things continue as they are, urban and suburban growth of 50% and 80% respectively will reduce available agricultural and vegetated lands by 500,000 to 620,000 square miles.
  • Changes in land cover (from human and climate drivers) can impact the climate by altering regional and global circulation patterns, changing earth’s albedo and changing the amount of CO2 in the atmosphere.
  • Urbanization often includes construction materials that absorb more heat than vegetation and soils, and building architecture tends to trap heat, leading to the urban heat island effect that amplifies the public health threat of heat waves in cities.
  • Climate change is expected to directly and indirectly impact land use and cover by altering disturbance patterns, species distributions, and suitability of land uses.
  • Climate change has broad implications for food security, and almost ⅔ of the recent land area converted for energy use was due to biofuel expansion — by 2040, the amount of new land area impacted by energy development could exceed the size of Texas.
  • The combined trends of urbanization (more paving less plant cover) and climate change will increase the risk and magnitude of flooding.

Chapter 6: Forests

  • Climate change will alter forest productivity and health, and jeopardize the species who live there as more frequent extreme weather events harm ecosystems and change in forests.
  • The fact that bugs are killing more trees than ever is likely related to climate change, as winters are no longer cold enough to keep mountain pine beetles in check as their ranges expand.
  • Drought and insects have killed hundreds of millions of trees in the past 20 years and wildfires have burned at least 3.7 million acres every year in all but 3 years from 2000 to 2016.
  • Higher temperatures have increased wildfire season in some parts of the western US, and by 2100 the annual area burned could increase 2-6 times.
  • A warmer climate is expected to increase damage from native insects on trees, and in the past 30 years, more trees in the western US have died from bark beetles than wildfires
  • A six-year drought in California (2011–2017) incited western pine beetle outbreaks,
    which contributed to the death of 129 million trees since 2010. In some areas, 70% of trees were lost in a single year.
  • In fall 2016, a prolonged dry period and arson in the southern Appalachian region resulted in 50 major wildfires that burned over 100,000 acres in 8 states and caused 15 deaths. As drought or prolonged dry periods increase, the southeastern United States will experience a longer fire season and greater fire risk.
  • Heavy rainfall can cause tree mortality and lead to soil erosion, which releases carbon stored in the soil.
  • Adaptation planning tools and options for forest resources are now institutionalized in public land management in many places.

Chapter 7: Ecosystems, Ecosystem Services, and Biodiversity

  • The natural systems we identify with as our local natural heritage- be it the mountains of Appalachia, the prairies of the midwest or the forests in the Pacific Northwest- have begun to change as temperatures rise and seasons shift in response to climate change.
  • Plants and animals have already begun moving and changing behaviors in response to climate change, but unless the pace of change is slowed it will outpace the speed of natural adaptations.
  • In the coastal Southeast, small changes in the frequency and intensity of winter freeze will turn wetland salt marshes into mangroves.
  • In the Southwest and Northwest, warmer waters and increasing variability in steamflow is endangering salmon a critical aspect of economic wellbeing and cultural heritage. Similar water temperature issues are playing out in streams and rivers across the country, with implications for cold water trout fishing, for example.
  • In Hawaii, nearly half of forest birds could lost 50% or more of their range by 2100 due to rise in avian malaria.  
  • Climate change impacts on ecosystems make it harder for them to improve water quality and regulate water flows.

Chapter 8: Coastal Effects

  • Sea level rise is increasing the frequency, depth and extent of tidal flooding, putting greater and greater amounts America’s trillion-dollar coastal property market and public infrastructure at increasing risks.  
  • Higher storm surges due to sea level rise and the increased probability of heavy precipitation events exacerbate the risk.
  • Continued emissions will transform coastal communities as chronic high tide flooding raises costs and lower property values.
  • Actions to plan for and adapt to more frequent and severe coastal flooding may decrease direct losses and cascading economic impacts.
  • Fisheries, tourism, human health, and public safety depend upon healthy coastal ecosystems. However, coastal ecosystems are being transformed, degraded, or lost due to climate change impacts, particularly sea level rise and higher numbers of extreme weather events.
  • Restoring and conserving coastal ecosystems and adopting natural and nature-based infrastructure solutions can enhance community and ecosystem resilience to climate change and help ensure the continued health and viability of these environments and our coastal communities.
  • As the pace of coastal flooding and erosion accelerates, climate impacts along our coasts are exacerbating pre-existing social inequities as communities face difficult questions on determining who will pay for current impacts and future adaptation strategies and if, how, or when to relocate vulnerable communities.
  • These questions challenge existing legal frameworks; coastal communities are among the first in the nation to test climate relevant legal frameworks and policies against these impacts. The answers to these questions will establish precedents that will affect both coastal and non-coastal regions.
  • With high emissions and no adaptation, cumulative damages to coastal property could be $3.6 Trillion, compared to $820 Billion with adaptation. (Fig 8.1)

Chapter 9: Oceans and Marine Resources

  • Continued carbon pollution will transform our oceans, with severe consequences for the 123 million Americans (39% of the total population) living in coastal counties and relying on oceans for food, employment, recreation, energy and other services.  
  • Climate change is already making our oceans hotter, more acidic and less oxygen-rich. These changes mean we are losing iconic and valuable habitats, as species migrate to cooler waters and food webs change.
  • Over 90% of the heat trapped by greenhouse gases is contained in oceans, which has warmed around 1.3F since 1900. This added warming impacts sea level, ocean circulation, stratification, and ecosystems.
  • It’s not just temperature. Oceans absorb carbon dioxide, which is already making the waters measurably more acidic. This acidity eats away at the calcium marine life uses to build shells and skeletons. Under high emissions, ocean acidification is expected to cause consumer losses of $230 million in the U.S. shellfish industry.
  • The majority of marine ecosystems in the US and around the world now experience ocean chemistry conditions that are entirely different than conditions prior to the Industrial Revolution.
  • Climate change is also causing a decline in ocean oxygen concentrations. Combined with agricultural runoff from the Mississippi River, which creates algal blooms and dead zones, deoxygenation of U.S. oceans is becoming a major economic stressor for ecosystems and fisheries.
  • Climate change is creating communities that are ecologically different from those that currently exist in ocean ecosystems.
  • Climate change has led to mass bleaching and coral disease in Puerto Rico, the U.S. Virgin Islands, Florida, Hawai’i, and the U.S.-affiliated Pacific Islands.
  • The loss of recreational benefits from coral reefs in the US is expected to reach $140 billion by 2100. Lowering GHG emissions could reduce these losses by $5.4 billion but there would still be ecological and economic impacts.
  • Fish species moving northward or to deeper water to escape warming water is causing trouble for the U.S. fishing sector, which contributes over $200 billion in economic activity each year and supports 1.6 million jobs.
  • Cod fisheries on each coast have been hurt by warming waters, resulting in economic stress in Gloucester, Massachusetts and cutting the available Pacific cod quota by 80% in 2018.
  • Fish catch potential is expected to be cut nearly in half under high emissions scenario in warm regions like Hawai’i, the Pacific Islands, the Caribbean, and the Gulf of Mexico. The nation’s most valuable fishery, the American lobster fishery, is expected to decline under the high emission scenario.
  • Native Americans depend on salmon and other fishery resources for both food and cultural value, and climate change will bring significant challenges to some place-based communities.
  • The combination of higher water temperatures, falling oxygen levels and increasing acidity of water will make unusual events like “the Blob” in the Pacific from ‘14 to ‘16 worse, and more common, severely disrupting ocean waters and the communities that rely on them.
  • For instance, in the Gulf of Maine in 2012, warm temperatures caused lobster catches to peak 3-4 weeks earlier than usual, causing a severe drop in price.

Chapter 10: Agriculture and Rural Communities

  • As warming increases drought frequency and duration, it will reduce crop yields, intensify wildfires on rangelands, deplete surface water, and accelerate of aquifer depletion.
  • The US spends $1B annually to fight wildfires but spent over $2B in 2015 due to extreme drought and spent over $2.9 billion in 2017.
  • Seed companies have released new crop varieties to adapt to a changing climate, and currently, the US has the largest gene bank in the world that manages publicly held crop germplasm.
  • Climate-smart agriculture and various farming adaptation methods (i.e. Changing fertilizer rates, selection of crop varieties, irrigation technology) can reduce the impacts of climate change and drought.
  • Challenges to human, crop, and livestock health are increasing due to increased frequency and intensity of temperature extremes.
  • Higher maximum temperatures can reduce crop yield and forage quality, increase the incidence of pests and disease for crops and livestock, and cause livestock heat stress.  
  • Interactive effects of rising carbon dioxide levels, higher temperatures, and other climate factors are expected to give weeds a competitive edge over crops.
  • Overall, higher temperatures are expected to lower yields for major crops and impact on specialty crops like fruits, nuts, and vegetables.
  • In 2000 the dairy industry experienced $897 million in losses from heat stress, and in 2010 the dairy industry lost $1.2 billion from heat stress. This was even though they had used adaptation-appropriate techniques. The beef industry lost $369 in 2000, pork down $299 million, and poultry $128 million.
  • Rural roads, bridges, and community water supply and sanitation are increasingly being damaged by large rainfall events. These sorts of extreme downpours have already become more frequent and intense, a trend that’s expected to continue.
  • Rural communities often have limited resilience to climate change due to poverty and limited infrastructure or access to resources.
  • Many rural communities are particularly vulnerable to climate change due to economic dependence on their natural resource base – forests, watersheds, rangelands, farmland, and fisheries, which are impacted by climate change.
  • The severe and extensive drought of 2012 led to losses in livestock, wheat, corn and soybeans that required a $14.5 billion payout from the federal crop insurance program.
  • Though the US has the largest gene bank in the world, public investment will be necessary to maintain the resources for genetic conservation.
  • Stronger rains increase runoffs, carrying more agricultural runoff into water supplies. This makes algae blooms and hypoxia events in natural bodies of water. Between 1960 and 2008, the US experienced a 30-fold increase in hypoxia incidences.

Chapter 11: Built Environment, Urban Systems, and Cities

  • U.S. metropolitan areas are home to 275 million people and account for 91% of U.S. GDP and 80% of North American greenhouse gas emissions. Climate change exacerbates existing challenges to urban quality of life, including social inequality, aging infrastructure, and stressed ecosystems.
  • Fortunately, cities are leading the way on responding to climate change and adaptation planning. Many U.S. cities participate in networks such as the U.S. Conference of Mayors, ICLEI, C40, and 100 Resilient Cities, which foster peer-to-peer learning, share best practices, and provide technical assistance to city staff.
  • Per Figure 11.2, cities around the US will see an increase in the number of “very hot days” in the 21st century – defined as above 90F for most cities, and above 110F for Phoenix, AZ, with implications for buildings, infrastructure, green spaces, and people.
  • At the highest emission levels, the report projects Pittsburgh would see the days above 90F rise from an average of 7.2 days per year in the 30 years through 2005 up to as many as 50 by 2050, and 100 by 2100 (on the highest emission trajectory). Fort Collins, CO, would see days above 90F rise from 5 days to 55 days.
  • Renters, people experiencing homelessness, children, the elderly, construction workers, and athletes are particularly susceptible to heat stress. And urban populations already experiencing socioeconomic inequality or health problems face greater exposure and susceptibility to problems driven by climate change.
  • Multiple impacts from climate change at the same time in one city can cause significant damage to the economy and to public health. For example, over four days in 2015, extreme rains, high sea levels and high tide flooding cause dam failures, bridge and road closures, power outages, home and business damage and a near shutdown of the Charleston, South Carolina economy.
  • Climate change also threatens the integrity of personal property, ecosystems, historic landmarks, playgrounds, and cultural sites such as libraries and museums.
  • Examples of infrastructure damage include flooding risks in transportation systems, the effects of sea level rise on coastal properties, reduced labor productivity in the construction and tourism industries, and adjusted risk portfolios in insurance and other industries.
  • Food security in urban areas is also threatened by climate change through loss of electricity for safe food storage, transportation disruptions along supply chains, and heat effects on agriculture.

Chapter 12: Transportation

  • Our transportation system, already face a $1.2 trillion gap in infrastructure needs, is at risk from heavy precipitation, coastal flooding, heat, and other impacts from climate change.
  • Climate change impacts like heavy rains and floods threaten our ability to use our transportation networks – things like roads, bridges and airports — which provide the skeleton of economic activity across the country, amounting to $400 billion of U.S. GDP.
  • As of 2016, the transportation sector was the largest contributor to US greenhouse gas emissions.
  • Climate change is projected to increase the costs of maintaining, repairing, and replacing infrastructure. Total annual damages in the U.S. from temperature- and precipitation-related damages to roads could reach $20 billion in 2090. Inland flooding, projected to increase over the coming century, threatens up to 4,600 bridges across the United States and is anticipated to result in up to $1.4 billion in annual damages by 2050.
  • We have spent billions of dollars repairing bridges and roads after damages from hurricanes since 2004, and coastal floodplains with over 60,000 miles of roads and bridges are already vulnerable to extreme storms.
  • Nearly all of our overseas trade comes through coastal ports, which are particularly vulnerable to sea level rise and hurricanes.
  • The amount of time coastal communities will be flooded by high tides every year is projected to nearly double by 2020, and 10-fold by 2060, even under a lower sea level rise scenario
  • By midcentury, extreme heat is expected to increase the number of days on which four major US airports must impose weight restrictions by 50%-200% because hotter air makes it harder for planes to generate lift.
  • Highway US 17 in Charleston, SC, is expected to experience increased flooding from 10 times annually today up to 180 floods annually by 2045, with each flood costing the city $12.5 million.
  • Extreme rains shut down parts of the Interstate Highway System for days or weeks at a time, like I-80 in California in the start of 2017. Increases in rain will threaten up to 4,600 bridges by 2050 and 6,000 bridges by 2090 under high a emission scenario.
  • A 2011 heat wave cost the Texas DOT $26 million, and increased heat events are expected to increase these costs in the future.
  • Climate change is expected to increase temperature-induced railway delay costs by up to $60 billion.
  • Rural areas are especially vulnerable to transportation system disruptions. In 2013 a 200-year flood event in Boulder, Colorado resulted in 485 miles of damaged or destroyed roadways and 1,100 landslide and hillslope failures cutting off many rural towns for weeks.
  • The Florida Keys roads were entirely cut off by Hurricane Irma in 2017.
  • Transportation network disruptions can disproportionately affect low-income and other vulnerable urban populations because these populations have fewer mobility options, reduced access to health care, and reduced economic ability to purchase goods and services to prepare for and recover from events.
  • Engineers, planners, and researchers in federal and other agencies are starting to assess the risks that climate hazards pose to transportation assets.  
  • Federal agencies and others are making funding available to study asset-specific and system-wide risks and vulnerabilities to transportation systems. The Federal Highway Administration funded 24 pilot studies between 2010 and 2015.

Chapter 13: Air Quality

  • Climate change driven increases in air pollution are increasing the risk of heart and lung problems, including premature death. 100 million Americans live in communities where air pollution doesn’t meet standards, and climate change will make air pollution worse.
  • Increased concentrations of ozone and particulate pollution across the U.S. due to climate change will enhance the risk of premature death due to adverse respiratory and cardiovascular outcomes. Children, the elderly and people with chronic illnesses are especially vulnerable to the health impacts of air pollution.
  • Climate change is also increasing the frequency of weather conditions that foster the buildup of ozone and particulate matter. Particulate matter is the name for liquid and solid particles made up of many different chemical components that are small enough to be suspended in the atmosphere. Particles with a diameter less than 2.5 micrometers are referred to as PM2.5 and believed to be particularly harmful because when they are inhaled they can travel through the lungs into the bloodstream.
  • The increased frequency and severity of wildfires due to climate change heightens the risk of harms to human health from wildfire smoke and its impact on air quality.
  • An estimated 40% of PM2.5 pollution in 2011 was from smoke from wildfires and prescribed fires. Wildfires may become the primary source of summertime PM2.5 concentrations.
  • Climate change is likely making allergic illnesses like hay fever and asthma more frequent and severe.
  • Emissions from fossil fuels not only drive climate change, but are also significant sources of air pollution that harms human health. Reducing the emissions sources that are driving this air pollution will make our air cleaner and lungs healthier.
  • Climate change driven increases in temperature and CO2 concentrations affect plant-based allergens, hay fever and asthma in three main ways. It is increasing the length of pollen season, increasing how much pollen is produced, and by making allergic reactions to pollen more severe.
  • Exposure to extreme heat events has been associated with greater incidence of hay fever. Also, the number of emergency-room visits for asthma are projected to increase in the Northeast, Southwest and Midwest because of climate-linked changes in oak pollen.
  • The energy sector is responsible for 84% of greenhouse gas emissions as well as 96% of sulfur dioxide (significant contributor to particulate matter), and 80% of nitrogen oxide emissions (which are an ozone precursor).
  • Mitigating emissions of methane, a strong GHG and contributor to surface ozone concentrations globally, can lower ozone levels, yielding substantial health benefits equal in scale to climate change mitigation benefits.
  • The risk of ozone-related premature death for a given level of ozone increases as temperatures rise.
  • In 2015, nearly a third of Americans were exposed to unhealthy ozone levels. Southern California and the Northeast corridor often experience the highest ozone levels, as do other large cities and anywhere experiencing extended periods of extreme heat and sunshine as ozone levels are often higher during heatwaves and sunny conditions.

Chapter 14: Human Health

  • Every American’s health is already at risk because of climate change, and consequences will worsen as temperatures rise.
  • Reducing emissions from the high to low scenario could save thousands of American lives and hundreds of billions of dollars a year by the end of the century.
  • The health risks of climate change are not experienced equally. Older adults, children, communities of color, and low-income communities are particularly vulnerable to climate change health threats.
  • Climate change increases public health risks through heatwaves, floods, droughts and other extreme events, diseases spread by pests and contaminated food and water, and the mental health consequences of these and other traumatic extreme events.
  • The 2015 California drought demonstrated that households in affected counties (Tulare and Mariposa) experienced drought-linked health impacts like asthma, allergies and other breathing issues, along with high stress levels. Those whose household property values and finances were negatively impacted felt more of these harmful mental and physical health effects.
  • In Arizona and California, drier conditions have led to an increase growth of the fungus that causes valley fever (coccidioidomycosis.)
  • Hotter summer temperatures increase the risk of illness and death, especially for the elderly, pregnant women and children. 
  • Hot days are linked to rising levels of heat-related illnesses like kidney failure, breathing and cardiovascular complications, preterm birth and electrolyte imbalance.  
  • Climate change is changing the range and abundance of vector-borne diseases, making for more favorable conditions for people to be exposed to pests carrying diseases, like mosquitoes carrying West Nile, Zika, dengue and Chikungunya and Lyme disease, carried by ticks.
  • Warming water temperatures will impact the growth and range of harmful algae blooms and coastal pathogens.
  • More intense rainfalls will also increase runoff, leading to more frequent pathogen contamination and toxic algae blooms in drinking water and recreational waters. Children and the elderly face the highest levels of risk from contaminated water.
  • Recent studies indicate that increasing CO2  concentrations are responsible for decreases in dietary iron.
  • Climate change may also increase exposure to salmonella and other food-borne pathogens and toxins.
  • Climate adaptation and incorporating climate change into infrastructure planning and urban design will reduce the risks to public health.
  • Reducing emissions will reduce the thousands of lives lost each year to climate change, and save us hundreds of billions of dollars of health costs.

Chapter 15: Tribal and Indigenous Communities

  • Climate change threatens Indigenous peoples’ livelihoods and economies. It has adverse impacts on cultural identities, threatens food security and disrupts communities and ecologies.
  • Indigenous agriculture is hurt by changing flood patterns, drought, dust storms, and rising temperatures, decreasing crop yields and increase the need for irrigation
  • A barrier to adaptation planning for Indigenous communities is the capacity of federally recognized tribes to implement water rights, with many communities have insufficient water delivery systems and a lack of capital to maintain and/or improve those systems
  • “Indigenous peoples along the coasts, the islands, the Southwest, and in Alaska have experienced the most extensive infrastructure-related impacts thus far.” (Figure 15.2)
  • Indigenous peoples have disproportionately higher rates of many health conditions that are directly linked to or exacerbated by or makes them more vulnerable to climate change impacts, like asthma, cardiovascular disease, Alzheimer’s or dementia, diabetes and obesity. (Box 15.1)
  • As the climate changes, indigenous peoples are less able or not able to share knowledge about the natural environment, food, and ceremonial or cultural objects because the knowledge is no longer accurate or traditional foodstuffs and species are less available due to climate change.
  • Many indigenous communities face obstacles to adaptation, including limited
    capacity to implement adaptation strategies, limited access to traditional territory and
    resources, and limitations of existing policies, programs, collaborations, and funding
    mechanisms.
  • A commitment to the principle of self-determination is critical for successful adaptation in indigenous communities.
  • Indigenous people’s own knowledge systems can play a role in advancing understanding of climate change and in developing more comprehensive climate adaptation strategies
  • Many tribes still experience historical trauma associated with loss of homelands and their traditional ways of life, which may be worsened by climate change impacts on cultural, land-use, and subsistence practices
  • When ecosystems and plant and animal habitats or migration routes shift due to climate change, it can be challenging for tribal members to adapt due to rights (such as gathering, hunting, or fishing) constrained by reservation borders
  • Some tribes with non-contiguous reservation lands can be negatively impacted by non-tribal landowners who do not support climate adaptation efforts, and many Indigenous peoples lacking federal recognition often lack governmental support to address climate change.
  • People are already being forced out of their homes by climate change. The state-recognized Isle de Jean Charles Band of Biloxi-Chitimacha-Choctaw of Louisiana, in partnership with the Lowlander Center, developed a community resettlement plan and in 2016 was selected, in conjunction with the state of Louisiana, to receive funding from the U.S. Department of Housing and Urban Development (HUD). Though promising, to date this solution is a pilot program through a one-time competitive funding opportunity and there is no planned ongoing support for other community-led resettlements.

Chapter 16: Climate Effects on U.S. International Interests

  • Climate change is affecting American economics and trade, international development and humanitarian assistance, national security, and transboundary resources.
  • Climate change is already impacting US military infrastructure, and further presents a risk to national security by presenting an additional stress on societies and potentially triggering conflict.
  • Climate change can lead to conflict by causing food and water insecurity, heightening resource competition and triggering commodity price shocks.
  • The Defense Department is working to both fully understand these threats and incorporate projected climate changes into long-term planning.
  • Climate change could lead to large-scale shifts in the availability and prices of a wide array of food, energy and other goods, which will impact the US economy.
  • Human migration is another potential national security concern. Extreme weather events can result in population displacement like in 2013, when Typhoon Haiyan displaced over 4 million people, and the US sent 13,400 military personnel to the relief effort.

Chapter 17: Sectoral Interdependencies, Multiple Stressors, and Complex Systems

  • Traditional approaches to assessing climate change and extreme weather impacts that focus on individual sectors will not yield the needed insights into understanding the interactions within and among these sectors, and how they might be impacted by other stressors.
  • It is not possible to understand the full extent of climate-related impacts on the United States without considering these interactions.
  • Climate change risk assessment requires evaluating how impacts interact across sectors and scales and how they can be shaped by multiple stressors.
  • Hurricane Harvey provided a clear example of what happens when climate-related stressors impact a tightly interconnected natural, built, and social system. Harvey caused power outages for 300,000 Texans,with a ripple effect in critical infrastructure like hospitals. It shut down 11 percent of US refining capacity in and a quarter of the Gulf’s oil production. Flooding inundated toxic Superfund sites and spilled untreated sewage from wastewater treatment plants.
  • More frequent and severe heat waves will increase stresses on electric power, as hot weather increases demand for electricity (mostly air conditioning) while reducing transmission efficiency
  • Heat or drought events, coupled with changes to population, urbanization, and economic development can have significant impacts on the demand for limited energy, water, or food resources.
  • Climate change and extreme weather will cause ripple effects through the movement of goods and people that could extend far beyond the area immediately impacted.
  • In 2013, Mississippi river barge traffic was reduced due to drought, forcing farmers to seek more expensive transportation options.

Chapter 18: Northeast Region

  • Rising temperatures, changing precipitation patterns, milder winters and earlier spring are already changing environments that impact human health. The Northeast can expect irreversible changes that impact hydrology, wildlife, and forests, which will impact tourism and human health.
  • Sea level rise three to four times higher than average is already impacting the region’s coasts, increasing high tide flooding by 100-200% in some places but increasing it by a factor of 10 or more over the last 50 years for many cities in the Northeast. By 2100, sea level rise will likely increase property losses from hurricanes to $11-17 billion, as property losses could rise to as much as $30 million for states like New Jersey and Delaware by 2100.
  • By 2050 and even under a low emission scenario, an estimated 20 cities in the Northeast will experience regular flooding, over 30 days a year.
  • “Ghost forests” are forming in southern New Jersey and Maryland as sea level rise pushes salt water into wetlands, causing forest diebacks,
  • Sea levels are likely to rise between 2 and 4.5 feet by 2100, but under worst-case scenario could be as over 11 feet.
  • Rising seas are imperiling beaches. Coastal property losses and the cost to protect property are estimated to cost anywhere from $15 billion in Massachusetts to over $30 billion for New Jersey and Delaware, regardless of low or high emission scenario.
  • Coastal communities are already impacted by declining fisheries, like cod, or moving ranges, like lobsters. Nearly half of the commercial fish species will be highly vulnerable to climate impacts by just 2050 under a high emission scenario.
  • The 2012 ocean heat wave showed how the lobster industry needs to adapt, as those conditions could be standard by mid-century.
  • Seasonal changes in open temperature have already started shifting fish migration, reproduction and other behaviors, with impacts being felt by the fishing industry.
  • Disruptions to infrastructure and historic sites are already occurring and will become more common.
  • A large number of communities are taking action to reduce risks of a changing climate and its impact on health, economies and ecosystems by implementing climate change adaptation.
  • Extreme heat poses a significant health risk, particularly to older or ill individuals, those without air conditioning, and outdoor workers. Continued warming will lead to more heat-caused deaths, hospital admissions and emergency room visits, with as many as 2,300 additional deaths a year by 2090 under the high emission scenario. Fighting climate change will save thousands of lives by 2090, saving $21 billion in health costs annually.
  • Warming is already bringing other health problems, increasing other dangerous air pollutants, smoke inhalation due to wildfires, lengthening and intensifying pollen seasons that worsen asthma and allergies, increasing mold growth indoors, increasing contamination in seafood and gastrointestinal illnesses, and spreading vector-borne diseases like Lyme disease and West Nile virus as ticks and mosquito ranges spread north. Reducing emissions would prevent around 360 deaths a year from air quality in 2090, saving $5.3 billion a year in health costs.
  • While improvements in air quality has saved lives in the Northeast, climate change threatens those gains. Because warmer weather makes for more ozone, fighting climate change is projected to save 200-300 additional deaths a year by 2050.
  • By making wildfires more common and severe, climate change is a threat to air quality, as smoke can spread thousands of miles. In 2015, Canadian wildfire smoke cuased Baltimore, Maryland to exceed its air quality limits.
  • The oyster-borne Vibrio bacteria has moved north, liekly increasing cases of food poisoning.
  • Warming has already led to snow melting earlier, and even under low emission scenarios project decreases in winter recreation spending. The Northeast winter recreation economy supports 44,500 jobs and generates as much as $2.7 billion in revenue every year is at risk from warming. A decrease in the average winter recreation season results in less natural snow and ice cover critical to snowmobiling, snowshoeing, cross-country skiing, and ice fishing. By 2090, these may not be economically viable.

Chapter 19: Southeast

  • The combined effects of extreme rainfall events and sea level rise are increasing flood frequencies, making these places highly vulnerable to climate change impacts. Without significant adaptation measures, many Southeast coastal cities will experience daily high tide flooding by the end of the century.
  • Climate change risks the health of Americans in the southeast by increasing exposure to heat, flooding, and vector-borne diseases, as well as worsening air quality.
  • A majority (61%) of Southern cities are already showing signs of stronger heat waves, and the night time temperatures have been increasing across the region, a trend which will continue with climate change.
  • Warmer winters allows the mosquitoes that carry diseases survive instead of freeze. That and warming temperatures throughout the region increases people’s potential exposure to diseases like dengue, Zika, and other diseases.
  • Extreme heat and changing seasonal climates will continue to put people’s health at risk and expose economic vulnerabilities in agriculture, timber, and manufacturing. By the end of century, over 500 million and as much as 830 million labor hours could be lost from extreme heat-related impacts.
  • Agricultural planting zones have already been shifted north to reflect warming. This will continue with further warming.
  • Pests like mosquitoes and tree-damaging beetles will move north with warming, putting people and timber at greater risk for disease and death.
  • Climate change is projected to reduce the south’s oyster harvest by 20% to 46%, depending on the amount of warming. This would raise the prices by 48% to 140%.
  • Some invasive species that kill native animals and replace native plants that are only kept in check by freezing winters, like Burmese python and Brazilian pepper tree in South Florida, will spread north as winters warm.
  • The Southeast could lose 570 million labor hours a year, costing $47 billion if emissions are not reduced and adaptation efforts not made.
  • Sea level rise is already causing a 5- to 10-fold increase in high tide flood events in several southern cities, and adding to the impact of more extreme coastal flooding events, which is already impacting property values and infrastructure viability.
  • Because climate change has caused sea level rise, high tide tidal flooding now poses a daily threat to the Southeast, and  will become widespread by the end of the century without adaptation measures. This will cost billions of dollars.
  • 2015 was a record year for coastal flooding in several southern cities. Wilmington NC  experienced 90 days of flooding, Charleston SC 38 days, Miami FL 18 days, and Key West Florida experienced two weeks of flooding. Regardless of future emissions, by 2050 many southern cities could experience a month, 30 days, of high tide flooding.
  • In 2014, Charleston SC experienced 11 days of high tide flooding. In 2015, it was a record 38 days. By 20145, the city could face 180 days of tidal flooding a year. The city has said each flood that affects the crosstown costs $12.4 million dollars.
  • If emissions are not reduced, damages from sea level rise and storm surge will cost the south $60 billion dollars a year by 2050, and $99 billion a year in 2090.
  • There are already 590,000 people in South Florida who the Florida Department of Health has determined are at an “extreme” or “high” risk from sea level rise. Of that, 55,000 are medically vulnerable, while 125,000 considered socially vulnerable.
  • There are already 7,508 miles of roads along the east coast that are threatened by high tide flooding.
  • Louisiana faces the highest land loss rates in the world. The Isle de Jean Charles Band of the Biloxi-Chitimacha-Choctaw Tribe is already resettling because sea level rise, land loss and coastal flooding has led to a 98% loss of landmass since 1955, as population has fallen to just 85 people. Wetland loss is happening at the rate of about a football field every 34 to 100 minutes.
  • Not only do 70% of rainfall records across the south shown an increase trend in rainfall, but the most intense events are becoming stronger and more frequent. Some, like the 2015 flooding in South Carolina, cause billions of dollars in damage, and deaths. They are expected to get more frequent and intense in a warmer world.

Chapter 20: U.S. Caribbean

  • Increasing global carbon emissions could lead to a steep reduction in rainfall in the Caribbean. This would reduce freshwater availability. Sea level rise and saltwater intrusion will reduce the quantity and quality of freshwater coastal aquifers. Increasing variability in rainfall and increasing temps will exacerbate existing water management problems.
  • Puerto Rico could lose up to 90% of its coral reef recreation value under most centuries by the end of the century as changes in species, loss of live corals, sponges, etc. will disrupt valuable ecosystem services and have subsequent effects on the economies.
  • Changes in ocean surface temperatures and acidity, seal level rise, and changes in the frequency and intensity of storms will further threaten access to freshwater.
  • Increased temperatures will likely lead to decreases in agricultural productivity, changes in habitat functionality, and increased risk to human health in vulnerable populations. Fewer cool nights and more hot days will impact quality of life.
  • Increasing frequency of extreme events threatens life, property and economy. Hurricanes, tropical storms, flooding, heat waves, and droughts are expected to increase. Resiliency will depend on collaboration and integrated planning, preparation, and response.
  • Shared knowledge, research and monitoring, and building institutional adaptive capacity through international cooperation can reduce the need for disaster relief, enhance food security, and improve economic opportunity.

Chapter 21: Midwest

  • By mid-century, the Midwest region is expected to see an additional 200 to 550 premature deaths per year by 2050 due to increased ozone levels, in addition to overall worsened health conditions and negative economic impacts. Climate change will bring new health threats through poor air quality, heat waves, heavy rainfall, more allergens, and more insect-driven diseases.
  • The Midwest is projected to have the largest increase in heat-related premature deaths by the end of the century – an additional 2,000 deaths per year in the high emission scenario.
  • Warmer, wetter conditions resulting from climate change are expected to hurt agricultural productivity.
  • Crop yields could decrease by up to 25 percent by mid-century for corn, and by more than 25 percent for soybeans, due to increased temperatures. Without adaptive actions, milk and egg production will be increasingly reduced due to temperature extremes by mid-century.
  • Rising humidity and warming winters have made it possible for existing pests, like the invasive emerald ash borer, to last longer and are allowing new pests to travel northward, threatening plants and trees. Changing climate conditions also tend to favor invasives over native species.
  • The economic value of timber in the Midwest is expected to decrease by up to $788 billion by the end of the century due to changes in forest composition.
  • Climate change is affecting the Great Lakes, which provide drinking water for 35 million people, through decreasing ice cover, increasing water temperatures, and increased evaporation, which can lower water levels and disrupt lake ecosystems and food webs.
  • Climate change is expected to bring more extremes, and transitions between wet periods and dry periods lead to harmful algal blooms in rivers and lakes, which can increase bacteria in lakes and rivers, impacting drinking water and recreation.
  • By 2050, increased temperatures will cost around $10 billion from premature mortality and lost work hours, and increased electricity demand is estimated to amount to $1.2 billion by 2090 with unabated climate change.
  • Additional climate and ozone-related deaths in the Midwest are estimated to cost $4.7 billion, half of the total projected deaths in the country.
  • By the end of the century, the Chicago is expected to experience anywhere between 23 and 63 days above 100F per year, compared to a handful of days like that now.
  • The Midwest has experienced increased pollen production and related allergies in recent years. Oak pollen is projected to be responsible for an increase of 88 to 350 emergency room visits for asthma by 2050, with an estimated increase in cost of care by a range of $43,000 to up to $170,000.
  • Increased precipitation is expected to cause mold growth in buildings, provoking asthma attacks and allergies, and transport pathogens that cause disease. Heavy flooding events can also cause mental and physical stress.
  • In the Midwest, climate-related ecosystem changes will result in more than 450 additional cases of West Nile Virus per year by 2090 if we don’t fight climate change.
  • Climate change is already bringing more flooding and precipitation to the Midwest region, which is impacting critical urban infrastructure like stormwater management and transportation. By the end of the century, Midwest is expected to spend more than $500 million per year to adapt urban stormwater systems to a changing climate.
  • Increased flooding in recent years has led to soil erosion and water quality issues from runoff into the Great Lakes.
  • Climate change is expected to increase road maintenance costs by $6 billion annually and cost over $1 billion annually in impacts to rail transportation by 2090.
  • Vulnerable communities and tribal nations in the Midwest are especially at risk from climate impacts. Working in partnership with these communities in adaptation planning will increase overall resilience to climate change.
  • Climate change will make it more $400 million dollars a year more expensive to keep bridges working by 2050 as climate change increases scour damages.

Chapter 22: Northern Great Plains

  • Effective water management is critical, and even small changes in precipitation can have large effects. Future changes in precipitation patterns and the potential for more extreme rainfall events will only serve to exacerbate these challenges.
  • We’re already seeing the sorts of weather whiplash that will be more common with climate change, for example flooding in 2011 followed by drought in 2012.
  • The number of heavy precipitation events are projected to increase significantly for much of the region.
  • In the mountains of western Wyoming and western Montana, the amount of water in precipitation that falls as snow instead of rain is expected to decline by 25%-40% by 2100.
  • In Wyoming and Montana, higher-than-normal winter and fall temperatures and low summer precipitation are enabling severe mountain pine beetle outbreaks in whitebark pine.
  • Transformative changes in agricultural management will likely be required to adapt to longer-term climate changes.
  • Local economies that depend on winter or river-based recreational activities are suffering from shorter snow seasons, lower summer streamflows, and higher stream temperatures.
  • In 2016, proliferative kidney disease killed thousands of native mountain whitefish in Montana, which triggered a month-long closure of 180 miles of the Yellowstone River to all water-based recreation. Initial estimates of the economic impact to local communities range from $360,000-$524,000.
  • The mountains of western Wyoming and western Montana are expected to get 25%-40% less snow by 2100, which will negatively affect the region’s winter recreation industry.
  • An estimated 50%-75% of all North American waterfowl hatch in the The North American Prairie Pothole Region (PPR), but in a warmer and drier climate, much of the PPR will be too dry to support waterfowl nesting and production. (Case Study)
  • Higher temperatures are expected to increase demands for electricity, which will increase costs to the power system of about $13–$18 million per year by 2050 and $42–$80 million per year by 2090 in a high emission scenario.
  • Greenhouse gas emissions from petroleum and natural gas facilities in this region are
    among the highest in the U.S. (Figure 22.6)
    Indigenous peoples in the region are at high risk from climate change impacts, especially hydrological changes. These changes are already hurting tribal economies, livelihoods, and sacred waters and plants, but many tribes have been proactive in adaptation and strategic climate change planning.
  • Tribes and Indigenous peoples are among those most at risk from climate change because many have high rates of poverty and unemployment, and many still directly rely on natural resources.
  • Climate change is already exacerbating the limited water availability, like in 2003 when Standing Rock Reservation ran completely out of water during a drought. Climate change impacts on water resources and indigenous peoples may be compounded by legal complexities, especially when state water laws supersede tribal water codes and water rights during times of scarcity, like when the Wyoming Supreme Court ruled the state has primary authority on the Wind River Reservation.
  • Indigenous people in the region are very concerned about major oil pipelines, in part because potential leaks could impact water resources already stressed by climate, and because climate change is projected to damage infrastructure, including pipelines.
  • Climate adaptations are underway by indigenous peoples in the region, but tribes face unique legal and regulatory barriers. For example, because the government holds tribal lands “in trust”, federal permission is required for many aspects of land and resource management.

Chapter 23: Southern Great Plains

  • Tropical, vector-borne diseases have recently begun appearing in southern Texas, like Zika, Chikungunya and Dengue.
  • Rising temperatures, increasingly extreme rainfall and rising sea levels will make cities more vulnerable to disruption, while coastal infrastructure will be at risk from sea level rise.
  • Temperatures in the region are projected to increase by up to 5.1F by 2050, and up to 8.4F by late 21st century.
  • Warming will bring an additional month or two of stiflingly hot summer temperatures: we can expect an additional 30-60 days a year above 100F, a doubling, by late 21st century. (Fig 23.4)
  • In 2017, Hurricane Harvey broke U.S. rainfall records, and was the latest in a string of record-breaking flooding in Houston, which experienced similar events in 2015 and 2016.
  • Extreme storms with the heaviest rainfall amounts, like Harvey, are 5-7% greater now than they would have been had they formed in the climate of a century ago.
  • Texas coasts have experienced 5-17 inches of sea level rise in the last 100 years, and will likely experience more than the global average of 1-4 feet over the rest of the century.
  • People and ecosystems will be hurt by extreme drought, unprecedented floods and wildfires, with future conditions potentially drier than anything the region has ever experienced over the last 1,000 years.
  • Health threats from extreme heat and vector-borne diseases will increase with warming.
  • When Texas experienced a summer 5.2°F higher than average, there was a measurable increase in emergency room visits (3.6%) and even deaths (0.6% increase.)
  • Each 1.8F of warming increases the death rate of elders with chronic conditions 2.8% to 4.0%.
  • Tribal nations and indigenous communities are particularly vulnerable to water impacts, extreme weather, high temperatures and other public health threats. Adaptation measures may be stymied by socio-political and infrastructure limitations, though traditional knowledge and intertribal organization may provide opportunities for solutions.

Chapter 24: Northwest

  • The region has warmed substantially—nearly 2°F since 1900—and this warming is partially attributable to human-caused emissions of greenhouse gases
  • Agricultural and fishery yields have already declined due to human-driven warming and ocean and precipitation changes, threatening Tribal and rural communities.
  • Over the last few decades, warmer and drier conditions during summer have contributed to longer fire seasons.
  • Wildfires smoke between 2004–2009 increased hospital admissions of adults over 65 by 7.2% in the western United States.
  • During extreme heat events in King County, Washington between 1990 and 2010, there were 10% more deaths than average.  
  • In seven of the 10 last years, Boise Idaho has experienced at least a week of smoke levels considered unhealthy for vulnerable people.
  • The Northwest is now experiencing cryptococcal infections, which prior to 1999 were strictly tropical.
  • A large outbreak of Shigellosis occurred in late 2015 affecting a large number of homeless people in the Portland-Metro region; this outbreak was associated with unusually extreme precipitation.
  • Abnormally low precipitation and extended drought events are expected to occur throughout the century. Extreme events, like heavy rainfall associated with atmospheric rivers, are also anticipated to occur more often.
  • Comparing high-snowfall to low-snowfall years in the Northwest between 1999 and 2009, the low-snowfall years resulted in 2,100 fewer employees and $173 million in reduced ski resort revenues.
  • In 2015, water temperatures in the lower Columbia River and tributaries were higher than at any other time on record, leading to a high rate of fish deaths. The record temperatures in 2015 were part of a long-term trend of declining low flows and warming streams.
  • In 2015, the increased ocean temperatures were part of an ocean heat wave coined the “Blob,” which fueled a coast-wide harmful algal bloom that impacted commercial, recreation, and tribal subsistence fisheries.
  • Largely as a result of climate change, forests in the interior Northwest are changing rapidly in the face of drought die-offs, increasing wildfire, insect and disease damage.
  • Climate change is threatening treasured features of life in the Northwest — from salmon runs to outdoor recreation — some of which are fundamental to Tribal cultures.
  • Increased steam temperature are expected to lead to a 22 percent reduction in salmon habitat in WA by late century if warming continues unchecked. It will result in $3 billion economic losses.
  • Impacts to wildlife will also impact sacred First Foods, or foods that Tribes have historically cultivated for subsistence, economic, and ceremonial purposes. The loss or decline of First Foods can have cascading physical and mental health impacts for Tribal and Indigenous peoples.
  • Future climate change will increase the risk of extreme events that already affect the Northwest, like wildfires and floods.
  • The Quinault Indian Nation has been flooded repeatedly, like when storm surge waters breached Taholah’s seawall in March 2014. The next year, roads were washed out by heavy rains. Because of these and other floods, the Nation is planning to relocate a lower village to higher ground.
  • In Tillamook County, Oregon, in December 2015, heavy rainfall coupled with high coastal water levels caused flooding that led to culvert failures, road closures, and reduced access to health facilities.
  • The Goodell wildfire in August 2015 forced Seattle City Light to de-energize transmission lines around its Skagit Hydroelectric Project for several days. The combined impact of damages and lost power production was nearly $3 million.
  • Throughout the Northwest, particularly Puget Sound and Portland areas could see 4.3 feet of sea level rise by the end of the century.
  • Beginning at the fetal development stage, environmental exposures to air or water pollution can increase the risk of impaired brain development, stillbirth and pre-term births. Infants and children can be disproportionately affected by toxic exposures because they eat, drink, and breathe more in proportion to their body size.
  • Airborne particulate levels from wildfires are projected to increase 160% by mid-century under a lower scenario, creating a greater risk of smoke exposure through increasing frequency, length, and intensity of smoke events.
  • Portland could see more than 80 additional heat-related deaths per year by mid century — without pollution abatement and future adaptations.
  • Farmworkers in the region can be particularly vulnerable to heat-related illness due to occupational exposure (heavy exertion and working outdoors), yet they often do not seek health care because of high costs, language barriers, and fear of deportation.

Chapter 25: Southwest

  • The Southwest has warmed by 1.6F since 1901, with more warm nights and fewer cold ones. Record high temperatures have been recorded in 2012, 2014, 2015, 2016, and 2017.
  • Extreme heat events and generally hotter temperatures have already led to heat deaths and illnesses in Arizona and California. A 2006 heat wave saw 600 more deaths, 16,000 more emergency room visits, and 1,100 more hospitalizations than is normal for summer days in California.
  • Warming under a high emissions scenario would cause an estimated 850 additional deaths a year by 2050, an economic loss of $11 billion that would double by 2090. The reducing emissions from high to low scenario cuts deaths and costs in half.  
  • Some parts of the southwest could see 45 more days per year above 90F by 2100.
  • Climate change is exacerbating drought in the region by decreasing snowpack, bringing spring warmth sooner in the year, decreasing relative humidity, and increasing the proportion of rain to snow. The warm winter of 2014-2015 saw the lowest snowpack in California on record, but by 2050 in a high emissions world, California mountains will receive only rain and no snow.
  • Climate change was a greater factor in area burned between 1916 and 2003 than was fire suppression, fire management or non-climate factors. Climate change doubled the area burned by wildfires across the west between 1984 and 2015, relative to what would have burned without warming.
  • Los Angeles experienced $3.1 billion in wildfire damages between 1990 and 2009, and breathing problems and other disruptions from one wildfire north of LA was estimated to cost $84 per person.
  • Continued emissions will bring more frequent and severe droughts, as well as an increase in fire frequency (25% more) an increase in very large fires (triple) and a tripling of area burned in California.
  • Climate change intensified recent droughts in California and the Colorado River Basin, with Lake Mead falling to its lowest level since creation in 1936. Higher temperatures are partly responsible for the record-setting drop in streamflow between 2000 and 2014. (Fig 25.3)
  • The 2015 drought in California cut over 10,000 agricultural jobs, and cost the state over $900 million in gross crop revenue.
  • The extensive death of pine trees across the southwest doubled between 1955 and 2007, a trend attributed to climate change’s increases in temperature, wildfire and bark beetles. Because of drought and warming winters, bark beetles killed 7% of western forests between 1979 and 2012.
  • Drought reduced hydroelectric generation in California by two-thirds between 2011 and 2015. Renewables can reduce future impacts of climate change, but also cut water needs for energy production by up to 90%. Converting two-thirds of fossil fuel power plants to renewables would cut water demand in half.
  • Atmospheric rivers, like the ones in the winter of 2016-2017 that led to the evacuations to avoid the expensive overflow of the Oroville Dam, may become more common and severe as the climate changes.
  • Renewable energy in the region has produced $5 billion in health benefits, and future benefits could reach $560 billion in saved healthcare costs.
  • Traditional foods important to Indigenous peoples, like corn, pine nuts, acorns and others, have already declined due to drought. Further reductions in vital fish, wildlife and other traditional foods and medicines are expected with warming. Indigenous adaptation to climate change will be reduced due to their unique socioeconomic and political constraints, though some tribes are already developing adaptation plans.
  • Warming has caused Yosemite National Park forests to change into sub-alpine meadows since 1880, as small mammals climbed 1,600 feet between 1914 to 2006.
  • With continued warming, Joshua Tree National Park, may no longer be suitable habitat for its namesake Joshua tree, as the American pika and numerous other bird species travel up mountains seeking cooler temperatures.
  • Sea levels on the west coast have risen around 9 inches, though local tectonic factors mitigate this in some places. Future warming could bring anywhere from two feet to six feet of sea level rise. A rise of three feet would put 200,000 Californians under water.
  • As much as $5 billion in property damages can be expected on the California coast due to sea level rise in a high emissions scenario.
  • A marine heat wave between 2014 and 2016, stacked on top of climate change-warmed waters, caused mass strandings of birds and sea lions, migrations of crabs and tuna out of the region, and closed commercial fisheries.
  • Ocean warming contributes to algae blooms, which in turn produce domoic acid, which can kill those who eat contaminated shellfish. This has already impacted the Dungeness crab fishing industry, which was delayed in 2015 and the catch was significantly reduced, because of the threat of domoic acid.
  • Carbon pollution has caused an increase in acidity of 25% to 40% from the preindustrial era.

Chapter 26: Alaska

  • Alaska is warming faster than any other state, and the North Slope is warming over twice as fast as the continental US.
  • 2016 was the warmest year in Alaskan records, and statewide average temperatures for 2014–2016 were notably warmer as compared to the last few decades.
  • In Alaska, starting in the 1990s, daily record high temperatures occurred three times as often as record lows, and in 2015, an astounding nine times as frequently.
  • Under a high emission scenario, by mid-century the highest daily maximum temperature is projected to increase 4°–8°F as compared to the average for 1981–2000. For the same future period, the lowest daily maximum temperature (the highest temperature of the coldest day of the year) throughout most of the state is projected to increase by more than 10°F. Lowest daily minimum temperatures (the coldest nights of the year) are projected to increase by more than 12°F.
  • Under a higher scenario, the number of nights below freezing would likely decrease by 20 nights per year in southern portions of the state, and by greater than 45 nights in coastal areas.
  • Under a higher scenario, annual maximum one-day precipitation is projected to increase by 5%–10% in southeastern Alaska and by more than 15% in the rest of the state.
  • Arctic summer sea ice declines already affect regionally important marine flora and fauna.
  • A new analysis released in 2016 suggests that corrosive conditions have been expanding deeper into the Arctic Basin over the last several decades. Pteropods play a critically important role in the Alaskan water food web and have been shown to be particularly susceptible to ocean acidification. The effect of ocean acidification on pteropods was demonstrated as severe shell dissolution, impaired growth, and also reduced survival.
  • The distribution of many ocean fish species is shifting northward as the ranges of warmer-water species expand and colder-water species contract in response to rising ocean temperatures, with the confirmed presence of 20 new species and 59 range changes in the last 15 years in the Chukchi and Beaufort Seas.
  • Climate change impacts that currently affect and will continue to affect Alaskans include permafrost thaw and increasing wildfires.
  • Degradation of permafrost is expected to continue, with associated impacts such as erosion and coastal flooding, damage to infrastructure, river and stream discharge, water quality, and fish and wildlife habitat.
  • Over 87% of Alaska Native communities are affected by flooding and erosion.
  • Two villages are already planning relocation efforts, but those and other plans face considerable challenges.
  • The frequency of big fire years (larger than 2 million acres) has been increasing, with three out of the top four fire years (in terms of acres burned) in Alaska occurring since the year 2000.
  • Glaciers continue to melt in Alaska, with an estimated loss of 75 ± 11 Gt per year ice volume from 1994 to 2013 , 70% of which is coming from land-terminating glaciers, and rates of ice loss are likely to increase, affecting stream flow and coastal food webs.
  • Additional adaptation would help protect Alaskans — particularly those in rural areas — from myriad health threats and poverty driven or exacerbated by climate change. These include injuries from flooding, loss of food sources, and psychological distress over disrupted traditional practices.
  • Higher winter temperatures and shorter duration of ice seasons may delay or disrupt usual patterns of ice formation on rivers, lakes, and the ocean. For hunters and other travelers, this increases the risk of falling through the ice, unplanned trip extensions, or cause travelers to attempt dangerous routes, leading to exposure injury, deaths, or drowning.
  • Tick-borne human illness are uncommon in Alaska, but new reports of ticks on domestic dogs without travel exposure outside Alaska raise concerns about tick range extension into Alaska and the potential for introduction of new pathogens.
  • Climate change is a common concern among Alaskans and is associated with feelings of depression and uncertainty about the potential changes to communities, subsistence foods, culture, and traditional knowledge and the potential of relocation from long-established traditional sites. These uncertainties and threats have effects on mental health and on family and community relationships and may lead to unhealthy responses such as substance abuse and self-harm.
  • Rising temperatures are damaging infrastructure in the state, and strategic repair and maintenance will be necessary to minimize expenditures.
  • A recent study (published in 2017) estimated a cost of $110–$270 million between 2015 and 2060 in maintenance and repair costs to mitigate or remediate damage from climate warming.
  • A recent estimate projected an increase in wildfire suppression costs of $25 million more per year above the 2002–2013 annual average).
  • As climate change progresses, proactive adaptation and collaboration with affected communities will continue to be key to maximizing the resilience of and opportunities available to Alaskans.

Chapter 27: Hawai’i and Pacific Islands

  • Water supplies for Pacific Island communities and ecosystems are threatened by rising temperatures, sea level rise, and increased risk of extreme drought and flooding.
  • Islands, especially low atolls, already experience saltwater contamination due to sea level rise, which is expected to catastrophically impact food and water security.
  • Pacific Islands are particularly vulnerable to climate change impacts due to their exposure and isolation, small size, low elevation, and concentration of infrastructure and economy along the coasts.
  • In Hawai’i, 2015 and 2016 were the warmest years on record. Hawai’i rainfall has been trending downward for decades, with the period since 2008 being particularly dry. It has also experienced more extremes, with heavy rainfall and droughts more common. (Figure 27.5)
  • Pacific Island ecosystems contain a high percentage of endemic species, and their biodiversity is both an important cultural resource for island people and the source of economic revenues through tourism.
  • Terrestrial habitats are threatened by climate change through rising temperatures, changes in rainfall, increased storms, and land-use changes, which could spread invasive species and threaten native species and human communities.
  • If the current emissions trajectory continues, all nearshore coral reefs in Hawai’i and American Samoa will experience annual bleaching starting in 2040, and in the Marianas beginning in 2035. (Figure 27.10)
  • Bleaching in 2015 killed on average 50% of the coral cover in western Hawai’i.
  • Nesting birds, turtles, seals, and coastal plants will be impacted the most because they are located near shorelines. Over half of the global populations of several seabirds species are located in the Hawaiian Islands.
  • The loss of arable land for food crops, along with the degradation of aquifers, is already causing problems for atoll communities that farm what they eat, and may cause some islands to become uninhabitable.
  • Sea level rise will likely force some atolls to be abandoned as they will no longer be able to support human residence if dramatic adaptation measures are not taken.
  • Even under moderate warming, 10 of the 21 forest bird species in Hawai’i will lose more than 50% of their range by 2100. (Figure 27.7)
  • Fisheries and the livelihoods they support are threatened by warmer ocean temperatures and ocean acidification. Bleaching and acidification will result in loss of reef structure, leading to lower fisheries yields and loss of coastal protection and habitat.
  • Widespread coral reef bleaching and mortality are increasing, and are projected to occur annually by midcentury.
  • Fishery productivity is expected to decline by up to 15% by 2050 and 50% under the higher scenario (RCP8.5).
  • Under high emissions, coral reef cover in Hawai’i is projected to decline from the current 38% to 11% in 2050, and to less than 1% by the end of the century. In the central and western Pacific, coral reef cover is projected to decline from the current 40% to 10-20% by 2050, and coral reef fish production is expected to decline by 20%.
  • In the central and western Pacific Ocean, maximum fishery yields are expected to decline by 2-5% per decade under high emissions.
  • Indigenous peoples of the Pacific are threatened by rising sea levels, future freshwater availability, and shifting ecosystem services, which imperil communities’ health, well-being, and modern livelihoods, as well as their familial relationships with lands, territories, and resources.
  • Indigenous women play a central role in island communities through teaching, practicing, protecting, and transmitting traditional knowledge and practices, and will help lead planning for future adaptations and actions.
  • Built on observations of climatic changes over time, indigenous knowledge transmission is intergenerational, place-based, localized, and vital for survival and ongoing adaptation.
  • Climate change threatens the familial relationship that indigenous communities have with ancestral resources, and is disrupting the continuity that is required for the health and well-being of these communities.
  • Because many island groups are very isolated, severe drought combined with saltwater intrusion can displace communities and cause failure of cultural, health, education, and economic systems.
  • As extreme events become more frequent, recovery from those events will prove increasingly difficult for isolated, resource-challenged islands and cause long-term declines in people’s welfare.
  • Combined with underlying economic vulnerabilities and stresses caused by unsustainable development, climate change may result in coral atolls becoming effectively uninhabitable, introducing issues of justice, sovereignty, and human and national security.
  • Climate change is already causing migration of individuals and communities, and increased relocation in the future will disrupt society-land relationships and loss of community identity. Resettlement has resulted in people facing landlessness, homelessness, unemployment, social marginalization, food insecurity, and increased levels of disease.

Chapter 28: Near-Term Adaptation Needs and Increased Resiliency

  • Many places are already experiencing climate impacts, and in just a few decades the US could lose hundreds of billions of dollars a year due to climate change. Short and long-term adaptation is needed to stem those losses, regardless of emission scenario.
  • We are not doing enough to adapt to climate change.
  • Adaptation planning and implementation projects have increased in the public and private sector since the last NCA but still not commonplace. Few projects address future impacts of climate change.
  • The assumption that the current and future climate will look similar to the historical record is harming successful adaptation while finding alternatives that work with America’s current expectations and infrastructure is challenging.
  • The authors recommend iterative risk management, which uses monitoring, research, evaluation and learning process, to address climate risk that will always change.
  • Initiatives such as policy changes, business operations and capital investments yield benefits greater than cost in the long-term as well as near-term. These benefits include economic, ecological, health, social, and security improvements.
  • Climate risk should be mainstreamed to be integrated with organization’s overall risk management.

Chapter 29: Mitigation- Avoiding and Reducing Long-Term Risks

  • Americans are already experiencing climate impacts from burning fossil fuels, and paying the price for these impacts. Reducing greenhouse gas emissions will reduce climate impacts and economic damages.
  • The Trump administration’s attempted regulatory rollbacks stand in stark contrast to the various city and state-level initiatives to fight climate change. For example, 455 cities support the global emission reduction efforts, and at least 110 local governments have greenhouse gas reduction targets, as to many states.
  • American health and wealth will be substantially affected by climate change.
  • Hundreds of billions of dollars in losses are possible for some sectors by the end of the century. That’s more than the current GDP of many states.
  • Adapting to climate change will reduce future damages significantly.
  • Sea level rise will lead to widespread impacts on coastal development for thousands of years, costing potentially hundreds of billions of dollars by the end of the century.
  • The difference between a low and high-emissions scenario is hundreds of thousands of deaths averted from extreme temperatures and air quality.
  • Reducing emissions will avoid nearly half of the $155 billion in lost wages from extreme heat by 2090
  • Though there are limited positive effects in some places for some times (less deaths from cold, for example) those effects will be swamped by negative impacts at broader scales.
  • High emission scenarios will require tens of billions of dollars of repairs for roads, bridges and railways.
  • Lost wages, particularly in the outdoor industry, due to extreme temperatures are projected to be as much as $160 billion annually by 2090.
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