Changes in Extreme Events

Changes in Extreme Events

Graphs comparing temperature observations (black line) from 1890-2000 with climate model simulations. The simulations that have only natural climate influences (blue lines) do not replicate the temperature pattern of the last 50 years. Including human contributions of greenhouse gases and sulfate aerosol pollution in the models (yellow lines) produces results that simulate the observations well.

We know that all weather results from a combination of interdependent factors, one of which is the warmer temperatures observed in the last 50 years. And computer models show that human emissions of greenhouse gases do account for much of that warming. So what does this mean for extremes in the US? Based on observations, model projections, and expert judgments, we can be confident of the following:

Cold Weather: Warmer and fewer cold days and nights

Car buried in a snowbank

Observations indicate that cold extremes are less frequent and milder. Climate models predict that trend is very likely to continue throughout this century.

Hotter and more frequent hot days and nights and heat waves

Sun behind clouds

Most of North America has experienced more frequent and intense heat extremes, which are also very likely to continue through the 21st century.

More frequent and intense heavy rainfall

Heavy rain falling near isolated trees.

Many areas in the U.S. have seen an increase in the heaviest downpours, and that pattern is very likely to continue in the future.

Increases in areas affected by drought

Hand holding dry dirt in a corn field

Regions that already experience long-duration droughts, such as the Southwestern U.S. and parts of Mexico and the Caribbean, will likely see the area affected increase.

More intense hurricanes

MODIS image of Hurricane Katrina prior to landfall on August 28, 2005.

Observations indicate an increase in hurricane intensity in the Atlantic and West Pacific (but a decrease in the eastern Pacific). Experts and models project those tendencies are likely to continue in the future.

Scientists are working to clarify what these changes might mean regionally or locally. For more information, see the modules, "Climate Change and Regional Impacts" and "Climate Change and Sea Level Rise."

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