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Climate Change Detection / Attribution Organizer: Martin Visbeck, Columbia University Co-organizer/Chair: Michael E. Mann, University of Virginia SPEAKERS: Gabi Hegerl, Duke University Drew Shindell, NASA-Goddard Institute for Space Studies National Academy of Sciences Thirteenth Annual Symposium on Frontiers of Science November 8-10, 2001 Climate Change Detection / Attribution Introduction (Mann) Q&A Use of Models in Detection/Attribution (Hegerl) Q&A Causes of N.Hemisphere winter warming (Shindell) Q&A Discussion National Academy of Sciences Thirteenth Annual Symposium on Frontiers of Science November 8-10, 2001 25 min 5 min 25 min 5 min 25 min 5 min 30 min Introduction to the Problem of Climate Change Detection and Attribution Michael E. Mann Department of Environmental Sciences University of Virginia National Academy of Sciences Thirteenth Annual Symposium on Frontiers of Science November 8-10, 2001 `There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activity' Intergovernmental Panel on Climate Change (United Nations), Third Assessment Report, 2001 OVERVIEW •The Empirical Record •Model Predictions •Comparison between the two •Key Outstanding issues THE EMPIRICAL RECORD Surface Temperature Changes Climatic Research Unit (‘CRU’), University of East Anglia Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001 TREE RINGS CORALS ICE CORES VARVED LAKE SEDIMENTS HISTORICAL DOCUMENTS INSTRUMENTAL TEMPERATURE RECORD GLOBAL PROXY CLIMATE RECORDS RECONSTRUCTED GLOBAL TEMPERATURE PATTERNS MODEL PREDICTIONS CO2 Related? Greenhouse Gases and Warming GREENHOUSE EFFECT? ENHANCED GREENHOUSE EFFECT? SIMULATED ANNUAL MEAN TREND 1949-1997 Knutson, T.R., T.L. Delworth, K.W. Dixon, and R.J. Stouffer, Model assessment of regional surface temperature trends (1949-1997), Journal of Geophysical Research, 104, 30981-30996, 1999. Modeled Natural Variability Observations COMPARISON BETWEEN MODEL AND OBSERVATIONS OBSERVED ANNUAL MEAN TREND 1949-1997 Knutson, T.R., T.L. Delworth, K.W. Dixon, and R.J. Stouffer, Model assessment of regional surface temperature trends (1949-1997), Journal of Geophysical Research, 104, 30981-30996, 1999. SIMULATED ANNUAL MEAN TREND 1949-1997 Knutson, T.R., T.L. Delworth, K.W. Dixon, and R.J. Stouffer, Model assessment of regional surface temperature trends (1949-1997), Journal of Geophysical Research, 104, 30981-30996, 1999. Inconsistent with Natural Variability Inconsistent with Greenhouse+ Sulphate Forcing Vertical Fingerprint Greenhouse vs. Solar Vertical Fingerprint ECHAM3/LSG MODEL Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001 CLIMATE FORCINGS Anthropogenic Greenhouse Gases Industrial Aerosols CLIMATE FORCINGS Volcanism 1000 1200 1400 1600 1800 Solar Natural 2000 Simulated Annual Global Mean Surface Temperatures Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001 Forced Model simulations Energy Balance Model (“EBM”) simulation Science Future Surface Temperatures Trends Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001 KEY OUTSTANDING ISSUES EL NINO/SOUTHERN OSCILLATION (“ENSO”) Substantial interannual climate variability associated with ENSO, but decadal variability is also evident as well. The recent decadal trend towards El Nino conditions could be natural or anthropogenic. Multivariate ENSO Index (“MEI”) NORTH ATLANTIC OSCILLATION Negative Phase Positive Phase NORTH ATLANTIC OSCILLATION Trend in NAO in past couple decades explains enhanced recent warming in certain regions of Northern Hemisphere The “Little Ice Age” Shindell et al (Science, in press) Empirical LIA winter cooling in Europe associated with an NAO trend due to solar irradiance changes, interacting w/ stratospheric atmospheric dynamics and chemistry NASA/GISS Model NORTH ATLANTIC OSCILLATION This NAO trend could be Anthropogenic CONCLUSIONS •Recent global surface temperatures are unprecedented this century, and likely at least the past millennium •It is difficult to explain the recent surface warming in terms of natural climate variability •Recent surface warming is largely consistent with simulations of the effects of anthropogenic influence on climate •Unresolved issues regarding the precise sensitivity of the climate to forcing, and changes in ENSO, NAO, and regional responses