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Ok, maybe not the sky itself… but the clouds. According to recent research by climate scientists in New Zealand, global cloud heights have dropped.

Researchers at The University of Auckland have reported a decreasing trend in average global cloud heights from 2000 to 2010, based on data gathered by the Multi-angle Imaging SpectroRadiometer (MISR) on NASA’s Terra satellite. The change over the ten-year span was 30 to 40 meters (about 100 to 130 feet), and was mostly due to fewer clouds at higher altitudes.

It’s suspected that this may be indicative of some sort of atmospheric cooling mechanism in play that could help counteract global warming.

“This is the first time we have been able to accurately measure changes in global cloud height and, while the record is too short to be definitive, it provides just a hint that something quite important might be going on,” said lead researcher Professor Roger Davies.

A steady reduction in cloud heights could help the planet radiate heat into space, thus serving as a negative feedback in the global warming process. The exact cause of the drop in cloud altitude is not yet known, but it could reasonably be resulting from a change in circulation patterns that otherwise form high-altitude clouds.

Cloud heights are just one of the many factors that affect climate, and until now have not been able to be measured globally over a long span of time.

“Clouds are one of the biggest uncertainties in our ability to predict future climate,” said Davies. “Cloud height is extremely difficult to model and therefore hasn’t been considered in models of future climate. For the first time we have been able to accurately measure the height of clouds on a global basis, and the challenge now will be to incorporate that information into climate models. It will provide a check on how well the models are doing, and may ultimately lead to better ones.”

While Terra data showed yearly variations in global cloud heights, the most extreme caused by El Niño and La Niña events in the Pacific, the overall trend for the years measured was a decrease.

Continuing research will be needed to determine future trends and how they may impact warming.

“If cloud heights come back up in the next ten years we would conclude that they are not slowing climate change,” Davies said. “But if they keep coming down it will be very significant.”

The team’s study was recently published in the journal Geophysical Research Letters.

Terra is a multi-national, multi-disciplinary mission involving partnerships with the aerospace agencies of Canada and Japan. An important part of NASA’s Science Mission, Terra is helping scientists around the world better understand and protect our home planet.

Read more on the NASA/JPL news release here.