Last updated October 4, 2019

Winter Storm Risk Increase

Climate change is making extreme cold events less likely on average, but it is also increasing the frequency of extreme snowfall events. Climate change is also linked to the destabilization of the jet stream, which can lead to outbreaks of Arctic air.[1]

One of the clearest changes in the weather across the US is the increasing frequency and intensity of heavy precipitation. A warmer atmosphere holds more water, and storms supplied by climate change with increasing moisture are widely observed to produce heavier rain and snow.

Climate science at a glance

  • The number of record-breaking precipitation events globally has significantly increased in recent decades, and the fingerprint of global warming has been documented in this pattern.
  • Extreme precipitation events are some of the clearest impacts of climate change on extreme weather.
  • An increase in precipitation rates is one of the more confident predictions of the effects of climate change on storms.[1]
  • On average, climate models suggest that early autumn extreme snowfall events in the US are less likely due to human-caused climate change.[2][3]
  • Extreme weather outbreaks tied to Arctic warming and a destabilized jet stream can lead to outbreaks of Arctic air in the US that break cold temperature and snowfall records even as the average temperature increases.

Background information

Warmer air increases precipitation extremes because it can hold more water

Warmer air holds more water because the water vapor molecules it contains are moving at a higher average speed than those in colder air making them less likely to condense back to liquid. According to the Clausius–Clapeyron equation, for each 1°C of warming, saturated air contains 7 percent more water vapor, which may precipitate out if conditions are right.[4] The average moisture content of the atmosphere has increased by about 4 percent since the 1970s, as expected from the Clausius–Clapeyron law.[5]

Storms reach out and gather water vapor over regions that are 10-25 times as large as the precipitation area, thus multiplying the effect of increased atmospheric moisture.[6] As water vapor condenses to form clouds, rain, or snow, the conversion releases heat that add buoyancy to the air and further fuels the storm.[7] This increases the gathering of moisture into storm clouds and further intensifies rain and snowfall.[6]

Storms are fueled by available heat. Increasing surface land and ocean temperatures are increasing the potential energy available to passing storms.[4]

Climate change destabilizes the jet stream

Climate change is making extreme cold events less likely on average, but it is also increasing the frequency of extreme precipitation, and destabilizing the jet stream. When the jet stream is destabilized, it can contort sharply towards the poles with ridges of high pressure and dips to the equator with troughs of low pressure. This extreme configuration is getting stuck in place which means that places are getting long periods of extreme weather. The result is that certain areas and seasons are getting a lot more blizzard weather, while in other areas, blizzards are less common.

US winter storm trends and climate change

  • NOAA scientists, examining 120 years of data, found that there were twice as many extreme regional snowstorms in the US between 1961 and 2010 compared to 1900 to 1960.
  • On average, climate models suggest that early autumn extreme snowfall events in the US are less likely due to human-caused climate change.[2][3]
  • According to the US Fourth National Climate Assessment, "Heavy precipitation events [defined as the heaviest 1 percent of all daily events] in most parts of the United States have increased in both intensity and frequency since 1901."[8]
  • From 1958 to 2016, the amount of precipitation falling in very heavy events (the top 1 percent of all daily precipitation events) increased by 55 percent in the Northeast, 27 percent in the Southeast, 42 percent in the Midwest, 29 percent in the Northern Great Plains, 12 percent in the Southern Great Plains, 10 percent in the Southwest, and 9 percent in the Northwest.[8]
  • The heaviest precipitation events have become more frequent across most of the country, and projects that heavy precipitation events that historically occurred once in 20 years will occur as frequently as every 5 to 15 years by late this century.[9]
  • In the past century, the US has witnessed a 20 percent increase in the amount of precipitation falling during the heaviest storms.[10]

US studies attribute increases in winter storm risk to climate change

  • (Wang et al. 2018): Data shows a likely effect of anthropogenic warming on the December 2015 extreme precipitation event in Missouri.[11]
  • (Trenberth et al. 2015): During "Snowmaggedon" in February 2010, high sea surface temperatures linked to human caused global warming fed moisture into the storm, helping it to intensify and causing heavy precipitation.[12]
  • (Edwards et al. 2015): An early October blizzard in South Dakota is determined to be climatologically anomalous. Climate models suggest that early autumn extreme snowfall events in western South Dakota are less likely due to anthropogenic climate change.[2]
  • (Knutson et al. 2014): Seasonal and annual mean precipitation extremes occurring during 2013 in north-central and eastern US regions were attributable to anthropogenic and natural forcings combined.[13]

Global winter storm trends and climate change

  • Evidence suggests that Arctic amplification of global warming remotely affects mid-latitude regions such as the United States by promoting a weaker, wavier atmospheric circulation conducive to extreme weather.[14][15]
  • Multiple observational studies suggest that Arctic amplification has caused concurrent changes in the Arctic and Northern Hemisphere large-scale circulation since the 1990s.[16][17][18]
  • The 5th Assessment Report of the Intergovernmental Panel on Climate Change states: It is likely that since about 1950 the number of heavy precipitation events over land has increased in more regions than it has decreased. Confidence is highest for North America and Europe where there have been likely increases in either the frequency or intensity of heavy precipitation with some seasonal and regional variations. It is very likely that there have been trends towards heavier precipitation events in central North America.[19]
  • Global analyses show that specific humidity, which measures the amount of water vapor in the atmosphere, has increased over both the land and the oceans.[19]
  • During the past 25 years, satellites have measured a 4 percent rise in atmospheric water vapor that is in line with the basic physics of a warming world and computer modeling of our current climate.[20][21]

Global studies attribute increases in winter storm risk to climate change

  • (Diffenbaugh et al. 2017): An April 2017 study found that, from 1961 to 2010, global warming increased the likelihood of occurrence of the wettest five-day periods on record in 41 percent of the observed areas of the world.[22]
  • (Fischer and Knutti 2015): About 18 percent of the "moderate" (i.e. 1-in-3 year) daily precipitation extremes over land are attributable to warming, while a much larger share of very extreme events is attributed to warming.[23]
  • (Fischer and Knutti 2014): There is a distinct intensification of heavy precipitation events and hot extremes at local scales. Observed local trends across the globe for the period 1960–2010 are clearly different to what would be expected from internal variability.[24]
  • (Zhang et al. 2013) detect the effect of anthropogenic forcings in extreme precipitation observations in the northern hemisphere. They estimate that human influence has intensified annual maximum 1 day precipitation in sampled Northern Hemisphere locations by 3.3 percent on average.[25]
  • (Min et al. 2011) show that human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas.[26]
  • (Min et al. 2008): Decisively detects anthropogenic signals in extreme precipitation changes in global, hemispheric, and zonal band areas.[27]