If you get the feeling that heavy downpours are more intense than they used to be, you’re not imagining it. According to the National Climate Assessment, the most extreme precipitation events (those in the 99th percentile of intensity) have increased in every region of the contiguous states since the 1950s. As the map above shows, the rise in intensity has been greatest in the Northeast and least in the Southwest — and in all cases, climate scientists believe, the reason is simple: in a world warmed by heat-trapping greenhouse gases, there’s more evaporation, and the atmosphere can hold on to more water. And when that water vapor condenses as rain or snow, there’s more of it.

The present level of atmospheric CO2 concentration is almost certainly unprecedented in the past million years, during which time modern humans evolved and societies developed. The atmospheric CO2 concentration was however higher in Earth’s more distant past (many millions of years ago), at which time palaeoclimatic and geological data indicate that temperatures and sea levels were also higher than they are today.

The total heat content of the Earth has been rising at a relatively costant pace since about 1965. Most of the heat (about 80%) has been absorbed by the oceans.

The observed warming in the lower atmosphere and cooling in the upper atmosphere provide us with key insights into the underlying causes of climate change and reveal that natural factors alone cannot explain the observed changes.

Climate Facts

Atmosphere


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Increase in Extreme Precipitation Events 1958-2012
The warmer atmosphere holds more water (about 4% per degree F) and a likely result has been be the increase in severe precipitation events in the last 50 years in the United States
What do changes in the vertical structure of atmospheric temperature—from the surface up to the stratosphere—tell us about the causes of recent climate change?
The observed warming in the lower atmosphere and cooling in the upper atmosphere provide us with key insights into the underlying causes of climate change and reveal that natural factors alone cannot explain the observed changes.