Extreme events attributable to climate change: past and future

Extreme weather events such as life-threatening heat waves and record-breaking downpours are part of the natural climate system, but some kinds of extreme weather events have become more common in recent decades. Scientific advances are allowing researchers to determine the extent to which climate change contributed to some extreme weather events. This is the science of extreme event attribution.

The Bulletin of the American Meteorological Society (BAMS) publishes an annual collection of attribution studies it has judged to be rigorous. Ten reports exist so far, describing extreme events that can be attributed at various levels to climate change, including some that, based on analyses of historical data and natural variation, would not have occurred if not for the added influence of climate change.

• a spring drought in South China (2018)
• high surface temperatures during a Tasman Sea heatwave (2017)
• the overall global atmospheric heat record (2016)
• a persistent area of unusually warm water that lingered off the Alaskan coast, causing reduced marine productivity and other ecological disruptions (2016)

Studies gathered in the BAMS reports have found that climate change contributed to the occurrence or intensity of many recent extreme events, including:

• extreme rainfall in Hurricane Dorian (2019)
• a November cold outbreak in the eastern United States (2019)
• the total rainfall during mid-Atlantic warm-season flooding (2018)
• a heat wave in the Four Corners region of the United States (2018)
• a summer drought in the U.S northern Great Plains (2017)
• warm temperatures in the central equatorial Pacific during El Niño, which disrupted coral reefs and seabird populations (2016)
• tropical cyclones in the western North Pacific Ocean (2015)
• high-tide floods in southeastern United States (2015)
• record-breaking fires in California (2014)
• drought and a deadly heat wave affecting Texas and other U.S. states (2011)

Scientists’ confidence about how weather and climate extremes will change is growing. Projections from the Intergovernmental Panel on Climate Change’s 2021 report suggest that as human-caused global warming increases:

• In North America, heat extremes (including warm days, warm nights, and heat waves) will become more common and more intense. Cold extremes (including cold days and cold nights) will become less common and less intense.
• Heavy precipitation like rainfall and snowstorms will happen more often and more intensely, and this will cause more flooding. In North America specifically, these increases are “likely” if global warming increases up to 3.6 degrees Fahrenheit (or 2.0 degrees Celsius) over pre-industrial levels, and “very likely” if warming exceeds that level.
• Over the 21st century, only some parts of the world are projected to see more flooding. Many of these regional projections are not very certain, but globally there is a larger fraction of regions with a predicted increase than a decrease over the 21st century.
• Greater land area will be affected by droughts, which will happen more commonly and more intensely. In much of the United States, such as the central Great Plains, summer conditions will be drier.
• Tropical cyclones (a category that includes hurricanes) will likely become less common or stay the same globally, but a greater fraction of those storms will be more intense. These especially strong cyclones will become more common in particular in some parts of the western North Pacific Ocean.
• Severe springtime thunderstorms will become more frequent in the United States and occur over a longer season.
• Compound events, such as when heavy rain causes flooding or drought contributes to wildfires, will become more frequent. Unprecedented extremes will be more likely.