From floods and hurricanes to droughts and wildfires, climate change set the stage for numerous natural disasters across the U.S. in 2017. In this inaugural list, we rank ten of the year’s most noteworthy events by their “climate buzz,” as measured by the volume of climate change-related discussion they generated on Twitter and in the news. We identify the trends and physical processes behind each event fueled by climate change.
For more details on these events, follow the links or visit Climate Signals, a digital platform that identifies the long-term climate change trends behind extreme events as they unfold in real time. The platform hosts a database of climate change impacts organized as trends (the “signals”) and individual events. Also, see our list of this year’s major climate impacts around the world.
Scroll down and hover over each image to find out which event’s climate connections sparked the most conversation in the news and Twitterverse.
*For this exercise, we utilized social media analytics platform Crimson Hexagon’s buzz monitor tool, which scoured the web for specified types of content fitting ten different Boolean keyword searches.
1. HURRICANE IRMA
The top three spots in the inaugural 2017 rankings were captured by Irma, Harvey and Maria, the three hurricanes that made landfall in the U.S. this year as Category 4 storms – itself a record-setting triple whammy. These storms vividly illustrated three different ways that climate change is amplifying the damage done by tropical cyclones.
Hurricane Irma drove record-breaking “compound” coastal flooding in Jacksonville and Savannah. In these events, rainfall runoff met storm surge that rode in on waters elevated by sea level rise over the last 100 years, creating devastating flooding. Sea level rise is now dramatically amplifying the damage done when tropical cyclones make landfall along low-lying coastlines. Sea-level rise is allowing storm surge to travel much further inland. Researchers have measured how far sea level rise to date has extended the reach of storm surge for one hurricane, hurricane Sandy, where the additional damage incurred solely by sea level rise to date ran into the billions of dollars.
2. Hurricane Harvey
The historic floods driven by Hurricane Harvey were fueled by record-breaking rainfall so intense that the traditional statistical analysis tools developed by NOAA (“annual exceedance probability” analysis) measured it as 1-in-25,000 year rain, reflecting the fingerprint of global warming found in both the dramatic intensification of rainfall worldwide and in the record-setting rains dumped by Harvey.
A warmer atmosphere is now holding and dumping more water when it rains and warming seas are evaporating more readily, offering up more moisture to passing storms. As Harvey approached the coast of Texas, temperatures in the Gulf of Mexico were up to 7°F warmer than the average over 1961-1990.
3. Hurricane Maria
The Category 4 winds that leveled Puerto Rico during Hurricane Maria reflect the ongoing trend in the intensification of hurricanes driven, at least in part, if not largely, by global warming. The science linking climate change to the observed intensification of hurricanes also took a major step forward over the last twelve months, an advancement reflected in the November release of the U.S. National Climate Assessment that drew this connection with clear and direct language.
Hurricanes are heat engines fueled by warm tropical waters. Warming seas are increasing the potential energy available to passing storms, effectively increasing the power ceiling or speed limit for these cyclones. This trend is strongest in the Atlantic, where rising ocean temperatures correlate closely to an increase in Atlantic tropical cyclone strength.
“Human activities…have contributed to the observed upward trend in North Atlantic hurricane activity since the 1970s.” Key Findings, Chapter 9, U.S. National Climate Assessment, Volume 1, November, 2017.
4. California Deluge
Climate change in California is linked to weather whiplash: rapid switching from one type of extreme weather to another. Prior to 2017, California experienced a decade of largely dry conditions. During 2015—the warmest water year ever registered—snowpack was record-low on April 1, at only 5 percent of average.
The wet winter season of 2017 was noteworthy for the large number of extreme atmospheric rivers that produced record rainfall and flooding in the state. In January, two back-to-back atmospheric river storms brought heavy rain, mountain snow, and localized flooding to central California. In mid-February, heavy rainfall forced 200,000 from their homes and communities when flooding damaged both spillways of the Oroville Dam. Just one week later, another set of back-to-back atmospheric river storms caused record rainfall — first in Southern California, then in Northern California. The recently released U.S. National Climate Assessment notes that the severity of landfalling atmospheric river storms on the U.S. West Coast increases with increasing temperatures.
Climate change increases the risk of extreme precipitation and flooding. A warmer atmosphere holds and dumps more moisture, which means rainfall is increasingly concentrated into extreme precipitation events. At the same time, a rising portion of that precipitation is falling as rain rather than snow due to warming temperatures, increasing the risk of flooding.
5. Spring Snow/Rainfall and Floods
Winter Storm Stella brought snowfall totals of up to 42 inches and snowfall rates up to an “incredible” 7 inches per hour to the U.S. Northeast in mid-March. A warmer atmosphere can hold more water vapor when saturated, increasing blizzard risk as storms like Stella collect and dump that moisture as extreme snowfall, sleet and rainfall. There have been twice as many extreme regional snowstorms in the U.S. between 1961 and 2010 compared to 1900 to 1960.
Beginning in late-April, heavy rainfall of up to 15 inches over a multi-state region in the Midwest caused historic levels of flooding along many rivers. An impressively large area of 100- to 1,000-year rains inundated Missouri, and the Ozarks were hit by record-shattering flood crests. At least 22 people were killed, and insured losses exceeded 1.7 billion.
Increasing extreme precipitation is an observed global trend firmly attributed to climate change. A warmer atmosphere holds more water, and storms supplied by climate change with increasing moisture are widely observed to produce heavier rain and snow. In the US, the amount of rain or snow falling on very heavy days — defined as the heaviest one percent of rainy and snowy days — increased from 1958 through 2016 by 53 percent in the Midwest and 92 percent in the Northeast. There were also twice as many extreme regional snowstorms across the U.S. between 1961 and 2010 compared to 1900 to 1960.
6. High Plains Flash Drought
In early May, the U.S. Drought Monitor classified neither the Dakotas or Montana as being in a drought. By July, and with the arrival of a major, slow-moving heat dome, flash drought gripped all three states. Flash droughts refer to relatively short periods of low and rapidly decreasing soil moisture, driven by a lack of precipitation or warm temperatures. The drought in the High Plains featured both.
Climate change amplifies the intensity, duration and frequency of extreme heat events that can exacerbate drought conditions. Climate change also increases wildfire risk by influencing the variables that start and fuel fires. Finally, the heat dome that rapidly intensified drought conditions in July also has links to climate change.
The drought had far reaching impacts, contributing to one of Montana’s worst wildfire seasons on record and causing agricultural losses of $2.5 billion.
High Plains Drought 2017
7. California Bakes and Burns
After a record warm June through August, California experienced “the greatest statewide heat wave ever recorded” from late August through early September. Many locations broke daily, monthly, and all time temperature records. Most notably, San Francisco broke its all time heat record, reaching 106°F on September 1. The fingerprint of global warming has been identified in both the long-term warming in California as well as the early September heat wave event.
A few weeks after the record September heat wave, major fires in California wine country exploded in October 2017. The heat wave, along with years of record-breaking drought (2012-2016), an exceptionally wet winter (2016-2017), and a record-hot warm season (2017) primed California for the deadliest and most destructive fires in state history. Four of the fires from the event killed 40 people and are listed among California’s 20 deadliest wildfires on record. Four fires are also listed among the states 20 most destructive on record, destroying a total of 8,323 structures. Higher temperatures and extreme variability between wet and dry seasons has elevated wildfire risk by increasing the abundance and dryness of available fuel.
8. Plains on Fire
Extreme fire conditions in early March fueled major blazes in Kansas, Oklahoma, Colorado, and Texas. One blaze, encompassing Clark and Comanche counties along Kansas’ southern border with Oklahoma, was the largest wildfire on record in the state. The previous record was set just one year prior.
These fires are consistent with the long-term increasing wildfire activity observed in the western U.S. grasslands, activity driven by climate change trends in the Great Plains region. Since the 1970s, large grass and shrubland fires have increased by more than 100,000 acres per decade. Formal attribution work has identified the fingerprint of global warming in the record hot temperatures that swept across the U.S. east of the Rockies in February 2017, as climate change increased the likelihood of such heat by threefold. A 2017 study found that the total area burned by large wildfires in the Great Plains rose 400 percent over a three-decade study period (1984-2014).
9. Pre-Monsoon Extreme Heat
During the pre-monsoon season, the southwestern U.S. experienced record-breaking heat, a classic signal of climate change. June temperatures soared 15 to 30°F above normal from California’s Central Valley, to Las Vegas, and down to Phoenix. More than 40 flights out of Phoenix were delayed or canceled when temperatures exceeded the maximum operating temperatures of the planes.
“I think we are seeing with the airplanes, for instance, our systems, many of them are built to historical standards, not to standards of the changing climate we live in,” said Robert E. Kopp, Director of the Coastal Climate Risk and Resilience Initiative at Rutgers University. “As we push the climate out of the historical realm and into this new realm, we are starting to see some systems break down.”
This was the second of two back-to-back years of pre-monsoon extreme heat in the Southwest. Heat waves have become more frequent across the U.S. in recent decades, with western regions setting records for numbers of these events in the 2000s. The fingerprint of global warming has been identified in the long-term warming trend across the Western U.S.
10. Summer in Winter
From February 1 through 28, the U.S. broke 5,452 daily high maximum and 4,686 daily high minimum temperature records, compared to 213 daily low maximum and 84 daily low minimum records. There were 34 heat records broken for every cold record broken. Due to the historic and unseasonably warm and rainy weather, Chicago witnessed no measurable snow cover for the entire months of January and February for the first time in records dating back to 1884. February was one of Chicago’s warmest on record.
In a stable climate, the ratio of days that are record hot to days that are record cold is approximately even. However, in our warming climate, record highs have begun to outpace record lows, with the imbalance growing for the past three decades. Observed long-term trends towards shorter, milder winters and earlier spring thaws are altering the timing of critical spring events such as bud burst (the emergence of new leaves on a plant at the beginning of each growing season) and emergence from overwintering (the process by which some organisms pass through or wait out the winter season). In North America as a whole, the length of time in a calendar year when temperatures are consistently warm enough for agricultural activity lengthened by 6 days between 1982 and 2011. Warmer air temperatures, linked to human-caused climate change, have triggered significant reductions in snow cover extent over high northern latitudes during the last 100 years.