Global Climate Change: Past and Future

2006 Scott Margolin Lecture in Environmental Affairs

Middlebury CollegeMiddlebury VTMarch 7, 2006

Michael E. MannDepartment of Meteorology and

Earth and Environmental Systems Institute (ESSI)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

THE DATA

Climatic Research Unit (‘CRU’), University of East Anglia

Surface Temperature Changes

Greenhouse Gases and WarmingCO2

Related?

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HISTORICAL DOCUMENTS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”

CLIMATE MODELS

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

biosphere, and cryosphere

General Circulation Models take into

account the full three-dimensional structure of

the atmosphere and ocean

This alone doesn’t guarantee that they should do a good job in describing climate change!

GCMs do a fairly good job of

describing the seasonal cycle in

surface temperature

January Temp (observations)

January Temp (model)

Modeled Internal Natural Variability Observations

INFLUENCE OF EXTERNAL FACTORS

The climate is governed by external factors, including the intensity of solar output and volcanic aerosols

and greenhouse gas concentrations

Solar Variations

Solar Variations

The climate is governed by external factors, including the intensity of solar output and volcanic aerosols

and greenhouse gas concentrations

Volcanoes

The climate is governed by external factors, including the intensity of solar output and volcanic aerosols

and greenhouse gas concentrations

The climate is governed by external factors, including the intensity of solar output and volcanic aerosols

and greenhouse gas concentrations

GREENHOUSE EFFECT?

ENHANCED GREENHOUSE EFFECT?

SIMULATIONS OF CLIMATE CHANGE

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

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

Press, Cambridge, 2001

Future Surface Temperatures Trends?

Possible Impacts:

North American Drought

1998 Global Temperature Pattern

El Nino and North American Drought

El Nino vs. North American Drought over the Past Century

Increased Drought La Nina

El NinoLess Drought

Courtesy of E.Cook

Katrina

(Aug 28 ’05)

Destructive Potential of

Atlantic Hurricanes

Possible Impacts:

Rita

(Sep 21 ’05)

Destructive Potential of

Atlantic Hurricanes

Possible Impacts:

Wilma

(Oct 19 ’05)

Destructive Potential of

Atlantic Hurricanes

Possible Impacts:

Hurricane Statistics

P. J. Webster, G. J. Holland, J. A. Curry, H.-R. Chang Changes in Tropical Cyclone Number, Duration, and Intensity in a Warming Environment, Science, 309, Issue 5742, 1844-1846 , 2005.

Emanuel, K. (2005), Increasing destructiveness of tropical cyclones over the past 30 years, Nature, online publication; published online 31 July 2005 | doi: 10.1038/nature03906

Hurricane Statistics

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), 3477-3495.

Climatological Surface Temperatures January

[source: NOAA Climate Prediction Center][source: NOAA Climate Prediction Center]

Surface Temperature Pattern January ’06

[source: NOAA Climate Prediction Center]

Surface Temperature Anomaly Pattern January ’06

[source: NOAA Climate Prediction Center]

Temperature Anomaly Pattern (January ’06)

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

Press, Cambridge, 2001

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

•Possible impacts of anthropogenic climate change this century include increased drought conditions in the western U.S. and more destructive Atlantic tropical storms and 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.’’

Gavin Schmidt, Michael Mann

Eric Steig, William Connolley, Ray Bradley, Stefan Rahmstorf, Rasmus Benestad, Caspar Ammann, Thibault de Garidel,

David Archer, Ray Pierrehumbert