Precipitation Changes Linked To Global Warming
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April Flowers for redOrbit.com – Your Universe Online
According to Eliza Doolittle from “My Fair Lady,” the rain in Spain lies mainly on the plain. However, according to a new study from the scientists at the Lawrence Livermore National Laboratory (LLNL), the location and intensity of rain is changing around the globe, not only in Spain.
The study, published in the online edition of the Proceedings of the National Academy of Sciences, reveals that observed changes in global (ocean and land) precipitation are directly affected by human activities and cannot be explained by natural variability alone.
The distribution of precipitation is affected by emissions of heat-trapping and ozone-depleting gases through two mechanisms. First, increasing temperatures are expected to make wet regions wetter and dry regions drier. This is called thermodynamic change. Second, changes in atmospheric circulation patterns will push 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,” said Kate Marvel. “External influences such as the increase in greenhouse gases are responsible for the changes.”
Climate model predictions were compared with global observations from the Global Precipitation Climatology Project. The Project’s observations span from 1979 to 2012. The research team found that natural variability, such as from El Niño and La Niña, does not account for the changes in global precipitation patterns. Natural fluctuations in climate can lead to either intensification or poleward shifts in precipitation, however, it is very rare for the two effects to occur naturally together.
“In combination, manmade increases in greenhouse gases and stratospheric ozone depletion are expected to lead to both an intensification and redistribution of global precipitation,” said 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 research team identified a fingerprint pattern that characterizes response of precipitation location and intensity 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 said.
The researchers focused on the underlying mechanisms that drive changes in global precipitation and restricted the analysis to large scales where there is confidence in the models’ ability to reproduce the current climate. This, according to Bonfils, shows that “the changes observed in the satellite era are externally forced and likely to be from man.”