Researchers recently concluded that certain changes in precipitation could only be caused by human forces, and cannot be explained with nature alone.
The "location and intensity" of rainfall has been changing globally, and scientists believe it is all thanks to mankind, a Lawrence Livermore National Laboratory (LLNL) news release reported.
Human emissions are trapping heat inside Earth's atmosphere, which affects temperature and makes wet areas experience even more rainfall and dry areas even less. The environment-harming emissions are also changing atmospheric circulation, which can change storm patterns across the globe and subtropical dry zones towards the poles.
"Both these changes are occurring simultaneously in global precipitation and this behavior cannot be explained by natural variability alone," LLNL's lead author Kate Marvel, said. "External influences such as the increase in greenhouse gases are responsible for the changes."
The team looked at climate model predictions from the Global Precipitation Climatology Project using observations taken between the years of 1979 and 2012. The team found that "natural variability," such as El Niños and La Niñas, cannot be fully responsible for the apparent precipitation change. Natural phenomena have been known to intensify rainfall or move precipitation towards the poles, but it is extremely unusual for both of these things to occur at the same time.
"In combination, manmade increases in greenhouse gases and stratospheric ozone depletion are expected to lead to both an intensification and redistribution of global precipitation," Celine Bonfils, the other LLNL author said. "The fact that we see both of these effects simultaneously in the observations is strong evidence that humans are affecting global precipitation."
The researchers found a "fingerprint pattern" that characterized the simultaneous increase in precipitation and shift towards the poles.
"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.
"We have shown that the changes observed in the satellite era are externally forced and likely to be from man," Bonfils said.
