DOE-Led Team Helps Resolve Long-Standing Puzzle in Climate Change Science
Consistent with basic theoretical expectations, climate model experiments predict that greenhouse gas increases should lead to greater warming in the tropical troposphere (the lowest layer of the atmosphere) than at the tropical land and ocean surface. Until several years ago, most satellite and weather balloon records suggested that the tropical troposphere had warmed by substantially less than the surface. This apparent discrepancy between simulations and reality has been a major conundrum for climate scientists for nearly a decade. Now, an international team led by DOE scientist Benjamin Santer of Lawrence Livermore National Laboratory, has helped to resolve this conundrum. Using randomly generated temperature data with no human warming component, the team showed that the statistical test being used identified statistically significant trend differences a higher proportion of the time than would be expected by chance alone. When they modified the test to correctly account for uncertainty in estimating temperature trends from noisy observational data, there were no longer pervasive, statistically significant differences between simulated and observed tropical temperature trends. Using this corrected test, many of the more recently developed observational datasets used by the Livermore-led team showed larger warming in the troposphere than at the surface, consistent with climate model results.
Santer, B. D., P. W. Thorne, L. Haimberger, K. E. Taylor, T. M. L. Wigley, J. R. Lanzante, S. Solomon, M. Free, P. J. Gleckler, P. D. Jones, T. R. Karl, S. A. Klein, C. Mears, D. Nychka, G. A. Schmidt, S. C. Sherwood, and F. J. Wentz. 2008. “Consistency of Modelled and Observed Temperature Trends in the Tropical Troposphere,” International Journal of Climatology 28(13), 1703–22. DOI: 10.1002/joc.1756.