Study Finds Earth Drying as Clouds Move to Poles

     (CN) — Scientists say they have for the first time documented that clouds may already be shifting toward the poles — expanding subtropical dry zones — due to global climate change.
     In a study published Monday in the journal Nature, researchers from University of California-San Diego confirmed what many climate models of global change have predicted.
     “What this paper brings to the table is the first credible demonstration that the cloud changes we expect from climate models and theory are currently happening,” lead author Joel Norris said.
     The role of clouds in both cooling and heating the planet — reflecting solar radiation during the day and trapping solar energy at night — make them important variables in the climate.
     The study found that clouds have shifted to such an extent that subtropical dry zones — located between about 20 and 30 degrees latitude in both hemispheres — are expanding. Cloud tops are also moving higher into the atmosphere, researchers said.
     While cloud shift toward the poles has been predicted by climate models, the complex behavior of clouds has led to debate within the scientific community regarding how they respond to global warming.
     Part of this confusion is due to outdated or faulty tools scientists had used to record cloud data. This includes inconsistent satellite imaging and records of cloudiness that demonstrated inaccurate trends due to gradual degradation of sensors, changes in satellite orbit, instrument calibration and other factors.
     “I guess what was surprising is that a lot of times we think of climate change as something that’s going to occur in the future,” Norris told NPR. “This is happening right now. It’s happened during my lifetime — it was a bit startling.”
     Roughly 70 percent of Earth is covered by clouds at any given time. This, in addition to their constant movement, makes it difficult for scientists to properly study cloud formations. In clouds, scientists are essentially observing the behavior of trillions of tiny water droplets spread out over hundreds of miles.
     Scientists will have to make additional adjustments to compensate for new satellites launching into different orbits and instrumentation, which will enable further cloud analysis.
     Kevin Trenberth, a climate researcher at the National Center for Atmospheric Research in Colorado, pointed out that certain factors might limit the study’s accuracy.
     He noted that the time frame was fairly brief and included a period that is referred to as the global warming hiatus — a period of relatively little change in globally averaged surface temperatures between 1999 and 2013.
     “This is a very good attempt to try and get a handle on this, but I don’t think it’s the final answer,” Trenberth told NPR.

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