NCA4: Western U.S. Fact Sheet


Climate Change Already Worsening Weather in the West

The western United States has warmed nearly 2°F since 1900, and with that has come increased fires, drought and disease.

The wildfire season has grown, as reduced snowpack further makes fires more frequent and intense. The smoke from the fires is harming air quality, which is bad for our health, while other sorts of health problems, like cryptococcal infections, are spreading north as temperatures warm.

Climate change will bring more bad news like this to the West, unless emissions are reduced quickly and dramatically.

The National Climate Assessment, Volume 2 features a variety of information on climate change impacts across the Western United States. Here are some highlights.

Warming is Already Increasing Wildfire, Drought, Economic Losses and Health Risks:

  • The 2015 drought in California cut over 10,000 agricultural jobs, and cost the state over $900 million in gross crop revenue.
  • Climate change doubled the area burned by wildfires across the West between 1984 and 2015, relative to what would have burned without warming. Climate change was a greater factor in area burned between 1916 and 2003 than was fire suppression, fire management or non-climate factors.
  • Higher temperatures have lengthened the wildfire season in the western U.S., while reducing mountain snowpack, which increases wildfire risk.
  • The extensive death of trees across the Southwest doubled between 1955 and 2007, a trend attributed to climate change. The Northwest’s forests have experienced hotter, dryer conditions over the last two decades, increasing wildfires, insect and disease damage, and tree deaths.
  • Bugs are killing more trees every year than we’ve ever seen as warming allows pine beetles to survive the winter and expand their range. In the last thirty years, pine beetles have killed more trees in the west than wildfires.
  • Climate change has worsened recent droughts in California, the Colorado River Basin, and Rio Grande. Drought in California has led to the loss of over 10,000 agricultural jobs, and cost the state over $900 million in  crop revenue.
  • 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.
  • Carbon pollution has caused an increase in acidity of 25% to 40% from the preindustrial era.
  • Higher temperatures are partly responsible for the record-setting drop in streamflow between 200 and 2014.
  • Agricultural and fishery yields have already declined due to human-driven warming and ocean and precipitation changes, threatening Tribal and rural communities.
  • Between 1999 and 2009, each low-snowfall year resulted in more than 2,100 fewer employees and a $173 million reduction in ski resort revenues ($189 million in 2015 dollars) compared to the high-snowfall years.

Climate Change is Already Making Americans Sick:

  • Extreme heat events and generally hotter temperatures have 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.
  • During extreme heat events in King County, Washington between 1990 and 2010, there were 10% more deaths than average. 
  • Smoke from wildfires between 2004–2009 generated a 7.2% increase in adults over 65 going to the hospital for respiratory problems.  Breathing problems and other disruptions from one wildfire north of LA was estimated to cost $84 per person.
  • In 2015, the Northwest experienced its warmest year on record, triggering impacts from snow drought to algal blooms to a spike in cases of Salmonella and E-coli. These warm winter temperatures may be considered “normal” if emissions continue to rise.
  • An increase in Lyme Disease cases has occurred in the region and is associated with rising temperatures and changing tick habitat.
  • Cyrptococcal infections, strictly tropical prior to 1999, have spread northward and caused at least 76 infections in Oregon in 2015.
  • 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.

Extreme Events are Already Here:

  • A five-year drought in California (2011–2016) incited western pine beetle outbreaks,
    which contributed to the mortality of 102 million trees. In some areas, 70% of trees were lost in a single year. That drought reduced hydroelectric generation in California by two-thirds between 2011 and 2015.
  • 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. It also impacted the Dungeness crab fishing industry, which was delayed in 2015 and the catch was significantly reduced, because of the threat of domoic acid, which can be lethal if consumed. I
  • 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.
  • Atmospheric rivers in California are expected to grow stronger and more frequent as the climate changes. In the ‘16-’17 winter, a series of atmospheric rivers filled northern California reservoirs and overloaded the Oroville Dam, leading to expensive damage and the evacuation of people downstream.

These Trends Will Worsen with Warming:

  • 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.
  • The Northwest will continue to warm during all seasons under all future emissions scenarios, although the rate of warming will depend on the level of emissions
  • Atmospheric rivers will grow more frequent and intense with warming.
  • 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.
  • By 2100, the annual area burned by wildfires could increase 2-6 times.
  • The southwest could see 45 more days per year above 90F by 2100. Warming in 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.  
  • 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.
  • The warming trend may be particularly bad in certain mountain areas in late winter and spring, which will further exacerbate snowpack loss and increase the risk for insect infestations and wildfires.
  • 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.
  • More frequent wildfires and poor air quality are expected to increase respiratory illnesses in the decades to come.
  • By 2050, there will be a 20-80% increase in the proportion of annual total precipitation that is produced by the current top 1% of storms, particularly in northwestern states.
  • Portland could see more than 80 additional heat-related deaths per year by mid century — without pollution abatement and future adaptations.