Stereo measurements from the Multiangle Imaging SpectroRadiometer (MISR) on the Terra satellite show a one percent decrease in global cloud height in the first decade of this century. A paper published in the journal Geophysical Research Letters by scientists from the University of Auckland, New Zealand, shows that the average cloud height has declined 31 m from between March 2000 and February 2010. The MISR instrument uses nine cameras at different angles to produce a stereo image of clouds around the globe, allowing measurement of their altitude and movement.
Clouds affect the Earth's energy balance by reflecting Sunlight to space and by radiating longwave radiation to the Earth and to space. More low clouds tend to cool the Earth and more high clouds tend to warm the Earth.
Most of the reduction in cloud height was due to fewer high clouds. Low clouds radiate more heat to space than high clouds because they are warmer. The drop in average cloud height allows clouds to more effectively radiate energy to space and would be a strong negative feedback to CO2 induced warming.
Global climate models do not consider the effects of changes in cloud height. All climate models assume that clouds change with warming to amplify greenhouse gas induced warming.
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