New Observations And Climate Model Data

Over the past decade, scientific evidence from a variety of sourceshas implicated human-caused increases in greenhouse gases as a majordriver of recent climate change. A key argument used to rebut suchfindings relates to satellite records of temperature change in thetroposphere – the lowest layer of Earth’s atmosphere.

Until recently, climate modelers compared their simulations withtemperatures from a single satellite dataset, which showed slightcooling of the tropical troposphere since 1979. This region of theatmosphere is predicted to warm in climate model simulations thatinclude observed increases in greenhouse gases. The discrepancy intropical temperature trends has been used to cast doubt on thereliability of computer models, and on their usefulness for predictingfuture climate changes.

Three papers published in today’s edition of Science Express shedlight on this debate. The first two studies revisit temperature dataobtained from satellites and weather balloons, and provide compellingevidence that the tropical troposphere has warmed since 1979. The thirdstudy, led by scientists at Lawrence Livermore National Laboratory,finds that these new observational estimates of temperature change areconsistent with results from state-of-the-art climate models.

The computer models analyzed in the Livermore study show that in thedeep tropics, temperature changes in the troposphere are larger than atthe surface. This “amplification” effect is caused by the release ofheat when moist tropical air rises and condenses into clouds. The sizeof the amplification effect is very similar in nearly 50 simulationsperformed with 19 different models.

The new satellite and weather balloon data described in the firsttwo Science Express papers have amplification behavior that is inagreement with the model results and with basic physical theory.

“This strongly suggests that there is no longer any fundamentaldiscrepancy between modeled and observed temperature trends in thetropical atmosphere,” said Benjamin Santer, lead author of theLivermore-led Science Express paper and a scientist in LLNL’s Programfor Climate Model Diagnosis and Intercomparison. “The new observationaldata helps to remove a major stumbling block in our understanding ofthe nature and causes of climate change. Our work illustrates thatprogress toward an improved understanding of the climate systemrequires a combination of observations, theory and models.”

Santer led an international team of scientists, including Livermoreresearchers Stephen Klein, Karl Taylor, Peter Gleckler, Jim Boyle andCharles Doutriaux. Other team members were from the National Center forAtmospheric Research, Remote Sensing Systems of Santa Rosa, Calif., theNational Oceanic and Atmospheric Administration’s Air ResourceLaboratory, the Hadley Centre for Climate Prediction and Research,Lawrence Berkeley National Laboratory, NOAA’s Geophysical FluidDynamics Laboratory, the University of Washington, NASA GoddardInstitute for Space Studies and NOAA’s National Climatic Data Center.

Founded in 1952, Lawrence Livermore National Laboratory has amission to ensure national security and apply science and technology tothe important issues of our time. Lawrence Livermore NationalLaboratory is managed by the University of California for the U.S.Department of Energy’s National Nuclear Security Administration.