Scattering clouds may increase global warming

A new study has shown strong evidence that as the oceans warm, clouds appear to scatter, indicating that changes in these clouds may increase global warming.

The role of clouds in climate change has been a major question for decades.

As the earth warms under increasing greenhouse gases, it is not known whether clouds will dissipate, letting in more of the sun's heat energy and making the earth warm even faster, or whether cloud cover will increase, blocking the Sun's rays and actually slowing down global warming.

Now, a new study by researchers Amy Clement and Robert Burgman from the University of Miami's Rosenstiel School of Marine and Atmospheric Science and Joel Norris from Scripps Institution ofOceanography at UC San Diego has begin to unravel this mystery.

Using observational data collected over the last 50 years and complex climate models, the team has established that low-level stratiform clouds appear to dissipate as the ocean warms, indicating that changes in these clouds may enhance the warming of the planet.

Because of inconsistencies in historical observations, trends in cloudiness have been difficult to identify.

The team broke through this cloud conundrum by removing errors from cloud records and using multiple data sources for the northeast Pacific Ocean, one of the most well-studied areas of low-level stratiform clouds in the world.

The result of their analysis was a surprising degree of agreement between two multi-decade datasets that were not only independent of each other, but that employed fundamentally different measurement methods.

One set consisted of collected visual observations from ships over the last 50 years, and the other was based on data collected from weather satellites.

"The agreement we found between the surface-based observations and the satellite data was almost shocking," said Clement, a professor of meteorology and physical oceanography at the University of Miami.

The Hadley Centre model from the UK Met Office was able to reproduce the observations.

Together, the observations and the Hadley Centre model results provide evidence that low-level stratiform clouds, which currently shield the earth from the sun's radiation, may dissipate in warming climates, allowing the oceans to further heat up, which would then cause more cloud dissipation.

"This is somewhat of a vicious cycle potentially exacerbating global warming," said Clement.

"But these findings provide a new way of looking at clouds changes. This can help to improve the simulation of clouds in climate models, which will lead to more accurate projections of future climate changes," she added.