Global cloud patterns have changed since the 1980s, and scientists have found these shifts are consistent with predictions from climate model simulations. By analyzing satellite records over the last 30 years, storm cloud tracks are shown to be moving toward the poles, the height of the highest cloud tops are increasing, and subtropical dry zones are expanding; changes that likely have a further warming effect on the planet.
While weather-monitoring satellites have been recording cloud information for decades, the researchers came up with new analysis techniques to account for erroneous information and get a clearer picture of the data. The techniques helped eliminate inconsistent imaging caused by such issues as changes in satellite orbit and degradation of sensors.
"The authors used a new technique to remove spurious variability in the satellite cloud records due to a multitude of problems, including but not limited to changes in the satellites used to observe Earth's clouds and calibration," Stephen Klein, research scientist at Lawrence Livermore National Laboratory, told Gizmag. "After the technique is applied, it is more likely that the remaining variability in clouds represents true cloud changes."
As a result, the researchers can then point to computer climate simulations taking into account human influences that show current cloud patterns behaving in a similar manner. It's the first credible evidence that those cloud pattern changes expected to occur in a climate change model are actually happening.
"These changes are those predicted by theory and climate models to be the result of a warming of the planet," said Klein. "These changes can also occur through natural climate variability, but the analysis of the paper shows that natural climate variability cannot produce the same pattern of change as observed. Furthermore, the pattern of cloud changes observed do occur in climate models when they are forced by the increase in greenhouse gases that cause global warming. This suggests that the observed changes are the result of climate change."
Clouds are one of the biggest variables when it comes to climate, cooling the planet by reflecting solar radiation back into space, and also heating it by trapping solar energy. But cloud behavior is complex and the largest area of uncertainty for scientists as they try to understand and predict climate and forecast trends. Current cloud behavior has been found to increase solar radiation absorption, with less thermal radiation able to escape into space.
The researchers took into account natural climate change events, including the planet-wide recovery from the 1982 eruption of El Chichon in Mexico and the 1991 eruption of Mt. Pinatubo in the Philippines. Both had a net cooling effect on the planet for several years. Barring any further natural events, the researchers expect cloud trends to continue into the future, with global warming to increase along with greenhouse gas concentrations.
The study was conducted by a consortium of researchers from Lawrence Livermore National Laboratory, Scripps Institution of Oceanography, University of California, Riverside, and Colorado State University.
The findings were published in the journal Nature.