Global Climate Change: Past and Future

`The balance of evidence suggests that there is a discernible human influence on global climate ' Intergovernmental Panel on Climate Change (United Nations), Second Assessment Report, 1996

`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

`Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations’ Intergovernmental Panel on Climate Change (United Nations), Fourth Assessment Report, 2007

OBSERVATIONS

Surface Temperature Changes Boxes: back to mid 19 th century Gray: back to beginning of 20th century

Surface Temperature Changes

Internally Consistent Changes in Other Variables

Greenhouse Gases and Warming CO 2 Related?

ENHANCED GREENHOUSE EFFECT?

TREE RINGS

CORALS

ICE CORES

VARVED LAKE SEDIMENTS

HISTORICAL DOCUMENTS

RECONSTRUCTED GLOBAL TEMPERATURE PATTERNS

Reconstructed Surface Temperatures Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

Reconstructions of Northern Hemisphere mean temperatures for the last 1000 years and instrumental record (black line) From “Wikipedia”

Mt Kilimanjaro

Thompson, L. G., Mosley-Thompson, E., Davis, M. E., Lin, P. N., Henderson, K., and Mashiotta, T. A., 2003, Tropical glacier and ice core evidence of climate change on annual to millennial time scales, Climatic Change, v. 59, p

MODEL SIMULATIONS

The climate represents a coupled system consisting of an atmosphere, hydrosphere, biosphere, and cryosphere

General Circulation Models (GCMs) take into account the full three-dimensional structure of the atmosphere and ocean

Natural Volcanism Solar CLIMATE FORCINGS Crowley, T.J., Causes of Climate Change Over the Past 1000 Years, Science, , 2000.

CLIMATE FORCINGS Anthropogenic Greenhouse Gases Industrial Aerosols Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

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

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

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

Jones, P.D., Mann, M.E., Climate Over Past Millennia, Reviews of Geophysics, 42, RG2002, doi: /2003RG000143, 2004.

Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001 Future Surface Temperatures Trends?

Model Predictions Climate Change 2001: The Scientific Basis, Houghton, J.T., et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

Model Predictions

Possible Impacts? Warmer summer temperatures +less/no increase in continental precipitation = more frequent summer drought

Greenland Melting… (source: Arctic Impacts of Arctic Warming, Cambridge Press, 2004). Possible Impacts?

…Sea Level Rise

Possible Impacts? …Sea Level Rise +10 meters

Possible Impacts? …More Destructive Hurricanes Katrina (Aug ’05)

Possible Impacts? …More Destructive Hurricanes Rita (Sep ’05)

Possible Impacts? …More Destructive Hurricanes Wilma (Oct ’05)

Climate Model Predictions Knutson, T. K., and R. E. Tuleya, 2004: Impact of CO2-induced warming on simulated hurricane intensity and precipitation: Sensitivity to the choice of climate model and convective parameterization. Journal of Climate, 17(18),

Emanuel, K. (2005), Increasing destructiveness of tropical cyclones over the past 30 years, Nature, online publication; published online 31 July 2005 | doi: /nature03906 Hurricane Statistics

CONCLUSIONS Recent global surface temperatures are unprecedented in a long-term context 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 Possible impacts of anthropogenic climate change this century include increased drought, coastal flooding, and more destructive Atlantic Hurricanes

``RealClimate is a commentary site on climate science by working climate scientists for the interested public and journalists. We aim to provide a quick response to developing stories and provide the context sometimes missing in mainstream commentary.’’RealClimate Gavin Schmidt, Michael Mann Eric Steig, William Connolley, Ray Bradley, Stefan Rahmstorf, Rasmus Benestad, Caspar Ammann, Thibault de Garidel, David Archer, Ray Pierrehumbert