Global Climate Change: Past and Future

Straub Environmental Lecture Salem, OregonMay 31, 2007

Michael E. MannDepartments of Meteorology and Geosciences and

Earth and Environmental Systems Institute

Director, Earth System Science Center,Penn State University

`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 verylikely 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 19th century

Gray: back to beginning of 20th century

Surface Temperature Changes

Surface Temperature Changes

Internally Consistent Changes in Other Variables

Greenhouse Gases and WarmingCO2

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HISTORICAL DOCUMENTS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

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. 137-155.

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

1000 1200 1400 1600 1800 2000

Volcanism

Solar

CLIMATE FORCINGS

Crowley, T.J., Causes of Climate Change Over the Past 1000 Years, Science, 289 270-277, 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:10.1029/2003RG000143, 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