Contra Clouds?

A decade of measurements from space suggests that the average height of clouds worldwide has dropped 30 or 40 meters, a phenomenon that may mean the Earth is adjusting to global warming by enhancing its ability to radiate heat to space.

NASA/JPL-Caltech

Researchers at New Zealand's University of Aukland have collated a decade of data from the Multiangle Imaging SpectroRadiometer (MISR) on NASA's Terra Earth-observation satellite to map cloud height.  The instrument, which uses nine cameras to generate stereo data on cloud altitudes and movement worldwide, found an overall drop from 2000 to 2010.

Univ. of Auckland / NASA JPL-Caltech

The dataset isn't long enough to draw definite conclusions, says Roger Davies, a professor of climate physics who led the research published in the journal Geophysical Research Letters.

"If cloud heights come back up in the next 10 years, we would conclude that they are not slowing climate change," he says. "But if they keep coming down it will be very significant."

One factor affecting the drop in cloud height is the El Nino/La Nina currents. In this map blue regions indicate where cloud heights rise above La Nina conditions, and red shows where they fall. The stronger the relationship between the current and cloud height, the darker the color.

Univ. of Auckland / NASA JPL-Caltech

Launched in 1999, the Terra spacecraft is scheduled to continue operating through the remainder of this decade, according to the Jet Propulsion Laboratory, which funded the cloud-height research.

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