Tropopause Height As an Indicator of Climate Change

Studies of human influence on global climate change have focused mostly on changes in surface or atmospheric temperatures. But climate change should be manifest in a variety of climate variables, not just temperature. One variable that has just been examined for the first time from a climate-change standpoint is the height of the tropopause—the transition zone between the turbulently mixed troposphere and the more stably stratified stratosphere.

Figure 4   Changes in annual-mean pLRT patterns in four ECHAM climate-change experiments (panels a–d) and in the NCEP reanalysis (panel e). Changes are defined as the average over 1993–1997 minus the average over 1979–1983.

Santer et al. have examined changes in tropopause height, diagnosing the pressure of the lapse rate tropopause (p_LRT) from reanalyses of observational data and from integration of simulations performed with coupled and uncoupled climate models (Figure 4). (Lapse rate is the rapidity with which temperature decreases with altitude.) Simulated p_LRT trends over the past several decades are consistent with reanalysis results. The increase in tropopause height seems to driven by the warming of the troposphere by greenhouse gases and the cooling of the stratosphere by ozone depletion. Changes in tropopause height deserve further attention because they may be a useful “fingerprint” of human effects on climate.

INVESTIGATORS
M. F. Wehner, Lawrence Berkeley National Laboratory; B. D. Santer, J. S. Boyle, K. AchutaRao, C. Doutriaux, and K. E. Taylor, Lawrence Livermore National Laboratory; G. A. Meehl, W. Washington, and T. M. L. Wigley, National Center for Atmospheric Research; R. Sausen, German Aerospace Center; J. E. Hansen, R. Ruedy, and G. Schmidt, NASA Goddard Institute for Space Studies; E. Roeckner, Max Planck Institute for Meteorology.

PUBLICATION
B. D. Santer, R. Sausen, T. M. L. Wigley, J. S. Boyle, K. AchutaRao, C. Doutriaux, J. E. Hansen, G. A. Meehl, E. Roeckner, R. Ruedy, G. Schmidt, and K. E. Taylor, “Behavior of Tropopause Height and Atmospheric Temperature in Models, Reanalyses, and Observations: Decadal Changes,” J. Geophys. Res. 108, 10.1029/2002JD002258 (2003).

URL
http://www-pcmdi.llnl.gov/

Benjamin Santer Receives 2002 E. O. Lawrence Award

On September 26, Secretary of Energy Spencer Abraham named Benjamin D. Santer of Lawrence Livermore National Laboratory as one of the seven winners of the 2002 Ernest Orlando Lawrence Award. Each winner received a gold medal, a citation, and $25,000. Santer, a physicist, was honored in the Environmental Science and Technology category and is the first Lawrence awardee to be honored for research in climate modeling. The award cited “his seminal and continuing contributions to our understanding of the effects of human activities and natural phenomena on the Earth’s climate system.” Santer runs sophisticated computer models at NERSC and elsewhere to understand the nature and causes of global climate change. He was thrust into the public spotlight in 1995 as the lead author of one chapter of a United Nations report. The chapter dealt with scientific studies attempting to detect unusual climate change and attribute some part of that change to human influence. Its conclusion that “the balance of evidence suggests a discernible human influence on global climate,” was based on a two-year assessment of the scientific evidence by dozens of experts. This finding provoked considerable scientific and political debate. The panel’s report has served as a scientific foundation for international discussions on reducing greenhouse emissions. In 1998 Santer was named a MacArthur Fellow in recognition of his “originality, creativity, self-direction, and capacity to contribute importantly to society particularly in atmospheric science.” Santer and 12 co-authors received the Norbert Gerbier/MUMM award from the World Meteorological Organization for the paper “A Search for Human Influences on the Thermal Structure of the Atmosphere,” which was published in Nature in July 1996.