New Research from the Lawrence Livermore National Laboratory (LLNL) has shown that observed changes in global precipitation are directly affected by human activities and cannot be explained by natural variability alone.
The study compared climate model predictions with actual global precipitation observations between 1979-2012. The research team found that natural variability (such as El Ninos and La Ninas) does not account for the changes in global precipitation patterns. While natural fluctuations in climate can lead to either intensification or poleward shifts in precipitation, it is very rare for the two effects to occur together naturally.
Warming due to the increase in greenhouse gases in the atmosphere is expected to make wet regions wetter and dry regions drier, according to the LLNL report.
Storm tracks and subtropical dry zones will shift toward the poles due to changes in atmospheric circulation patterns.
"In combination, man-made increases in greenhouse gases and stratospheric ozone depletion are expected to lead to both an intensification and redistribution of global precipitation," said Celine Bonfils, the other LLNL author. "The fact that we see both of these effects simultaneously in the observations is strong evidence that humans are affecting global precipitation."
Key statement from the conclusion of the study from the Proceedings of the National Academy of Sciences of the United States of America....
We have identified a fingerprint pattern that characterizes the simultaneous response of precipitation location and intensity to external forcing and acts as a noise filter. Observed changes in this multivariate response are incompatible with our best estimates of natural variability and consistent with model predictions of externally forced change. The synchronicity of these changes is key, however: considering either change in isolation does not lead to detection and attribution . By focusing on both the underlying mechanisms that drive changes in global precipitation, and by restricting our analysis to the large scales where we have some confidence in models’ ability to reproduce the current climate, we have shown that the changes observed in the satellite era are externally forced, and likely to be anthropogenic in nature.
Images courtesy of NOAA.
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