According to a news release from the Lawrence Livermore National Laboratory, global precipitation changes are linked to global warming. LLNL scientists have revealed that observed alterations in global precipitation are directly impacted by human activities and cannot be explicated by natural variability alone.

Emissions of heat-trapping and ozone-depleting gasses impact the dispersion of precipitation via two systems. Rising temperatures are anticipated to turn wet regions into wetter regions and dry regions into drier regions; and alterations in atmospheric circulation patterns will force storm tracks and subtropical dry zones toward the poles.

“Both these changes are occurring simultaneously in global precipitation and this behavior cannot be explained by natural variability alone,” noted LLNL’s lead author Kate Marvel. “External influences such as the increase in greenhouse gases are responsible for the changes.”

The scientists examined in contrast climate model predictions with the Global Precipitation Climatology Project’s global observations, which take into consideration the year 1979 through 2012, and discovered that natural variability does not give reason for the alterations in global precipitation patterns. While natural variations in climate can result in either intensification or poleward shifts in precipitation, it is extremely rare for the two effects to take place together naturally.

“In combination, manmade increases in greenhouse gases and stratospheric ozone depletion are expected to lead to both an intensification and redistribution of global precipitation,” posited LLNL author Céline Bonfils. “The fact that we see both of these effects simultaneously in the observations is strong evidence that humans are affecting global precipitation.”

The scientists determined a fingerprint pattern that describes the concurrent response of precipitation location and severity to external forcing.

“Most previous work has focused on either thermodynamic or dynamic changes in isolation. By looking at both, we were able to identify a pattern of precipitation change that fits with what is expected from human-caused climate change,” Marvel added.

“We have shown that the changes observed in the satellite era are externally forced and likely to be from man,” Bonfils remarked.

The study’s findings are described in greater detail in Proceedings of the National Academy of Sciences.

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