NASA Satellite Finds Earth's Clouds are Getting Lower
A new university study using data from NASA's Terra spacecraft finds Earth's clouds got about one percent lower on average during the first decade of the 2000s.
Earth's  clouds got a little lower -- about one percent on average -- during the first  decade of this century, finds a new NASA-funded university study based on NASA  satellite data. The results have potential implications for future global  climate.Scientists  at the University of Auckland in New Zealand analyzed the first 10 years of  global cloud-top height measurements (from March 2000 to February 2010) from  the Multi-angle Imaging SpectroRadiometer (MISR) instrument on NASA's Terra  spacecraft. The study, published recently in the journal Geophysical Research  Letters, revealed an overall trend of decreasing cloud height. Global average  cloud height declined by around one percent over the decade, or by around 100  to 130 feet (30 to 40 meters). Most of the reduction was due to fewer clouds  occurring at very high altitudes.Lead  researcher Roger Davies said that while the record is too short to be  definitive, it provides a hint that something quite important might be going  on. Longer-term monitoring will be required to determine the significance of  the observation for global temperatures.A  consistent reduction in cloud height would allow Earth to cool to space more  efficiently, reducing the surface temperature of the planet and potentially  slowing the effects of global warming. This may represent a "negative feedback"  mechanism - a change caused by global warming that works to counteract it. "We  don't know exactly what causes the cloud heights to lower," says Davies. "But  it must be due to a change in the circulation patterns that give rise to cloud  formation at high altitude."NASA's  Terra spacecraft is scheduled to continue gathering data through the remainder  of this decade. Scientists will continue to monitor the MISR data closely to  see if this trend continues.For  more information, visit:http://www.auckland.ac.nz/uoa/home/news/template/news_item.jsp?cid=466683.MISR,  built and managed by NASA's Jet Propulsion Laboratory, Pasadena, Calif., is one  of five instruments on NASA's Terra spacecraft, launched in December 1999. The  instrument uses nine cameras at different angles to produce a stereo image of  clouds around the globe, allowing measurement of their altitude and movement. For  more on MISR, visit:http://www-misr.jpl.nasa.gov/. For more on Terra, visit:http://terra.nasa.gov/.Another NASA mission that studies  clouds is NASA's CloudSat, also built by JPL and launched in 2006. CloudSat is  the first satellite that  uses an advanced radar to "slice" through clouds to see their  vertical structure, providing a completely new observational capability from  space. CloudSat's primary goal is to furnish data needed to evaluate and  improve the way clouds are represented in global models, thereby contributing  to better predictions of clouds and thus to their poorly understood role in  climate change and the cloud-climate feedback. For information  on NASA's CloudSat mission, visit:http://cloudsat.atmos.colostate.edu/andhttp://www.nasa.gov/cloudsat.