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| Humans have an impact on rainfall through both air pollution and greenhouse gas emissions. Photo Credit: Patrick Hendry |
We know that greenhouse gas emissions like carbon dioxide should increase rainfall. The emissions heat the atmosphere, causing a one-two punch: warmer oceans make it easier for water to evaporate, and warmer air can hold more water vapor, meaning more moisture is available to fall as rain. But for much of the 20th century, that increase in precipitation didn’t clearly show up in the data.
A new study led by researchers at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) finds that the expected increase in rain has been largely offset by the drying effect of aerosols – emissions like sulfur dioxide that are produced by burning fossil fuels, and commonly thought of as air pollution or smog. The research is published today in the journal Nature Communications.
“This is the first time that we can really understand what’s causing extreme rainfall to change within the continental U.S.,” said Mark Risser, a research scientist at Berkeley Lab and one of the lead authors for the study. He noted that until the 1970s, the expected increases to extreme rainfall were offset by aerosols. But the Clean Air Act caused a drastic reduction in air pollution in the United States. “The aerosol masking was turned off quite suddenly. That means rainfall might ramp up much more quickly than we would have otherwise predicted.”
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