climate changes during the past millennium michael e. mann department of environmental sciences...

CLIMATE CHANGES DURING THE PAST MILLENNIUM

Michael E. Mann Department of Environmental Sciences

University of Virginia

Gavin A. Schmidt and Drew T. Shindell

Goddard Institute for Space Studies and Center for Climate Systems Research, Columbia University

AGU Fall MeetingDecember 2002

INSTRUMENTAL TEMPERATURE

RECORD

GLOBAL PROXY

CLIMATE RECORDS

Annual Resolution Proxy Climate Indicators

Note: half of the surface area is between 30S and 30N

Reconstructed Surface Temperatures

Mann, M.E., Bradley, R.S., Hughes, M.K., Global-Scale Temperature Patterns and Climate Forcing Over the

Past Six Centuries, Nature, 392, 779-787, 1998.

Reconstructed Surface Temperatures

Climate Change 2001: The Scientific Basis, Houghton, J.T.,

et al. (eds.), Cambridge Univ. Press, Cambridge, 2001

Mann, M.E., The Value of Multiple Proxies Science, 297, 1481-1482, 2002.

Esper, J., Cook, E.R., Schweingruber, F.H., Low-Frequency Signals in Long Tree-Ring Chronologies for Reconstructing Past Temperature Variability, Science, 295, 2250-2253, 2002.

Mid-Latitude Tree RingsGreater variability?

Mid-Latitude Tree Rings

1000 1200 1400 1600 1800 2000

Greater variability?

Shindell et al, 2002 (submitted)

Volcanic Radiative Summer Cooling

Average summer surface temperature response (June-August) in the ten winters immediately following eruptions for Pinatubo.

Average winter surface temperature response (December-February) in the ten winters immediately following eruptions for Pinatubo.

Shindell et al, 2002 (submitted)

Volcanic Winter Dynamical Warming

Long-term climateresponse to volcaniceruptions: GISS GCM ensembles

Pinatubo(12 years followingeruption)

Tambora(12 years followingeruption)

Time series(1959-1999)

-0.4 -0.7

-1.2 -2.1

-0.4 -0.6

dT dF C W/m2

Shindell et al, 2002 (submitted)

European Winter Cooling During the Little Ice Age

Negative pattern of sensitivity of Mann et al (1998) surface temperature reconstructions against the Lean et al (1995) solar irradiance series for the period 1650-1850 (20 year lag, 40 year lowpass)

Waple, A., Mann, M.E., Bradley, R.S., Long-term Patterns of Solar Irradiance Forcing in

Model Experiments and Proxy-based Surface Temperature Reconstructions, Climate

Dynamics, 18, 563-578, 2002.

Sunspots

LIA winter cooling in Europe associated with

an NAO trend due to solar irradiance changes,

interacting w/ stratospheric

atmospheric dynamics and chemistry

Empirical

NASA/GISS Model

European Winter Cooling During the Little Ice Age

Shindell, D.T., Schmidt, G.A., Mann, M.E., Rind, D., Waple, A., Solar forcing of regional climate

change during the Maunder Minimum, Science, 294, 2149-

2152, 2001.

Proxy basedreconstruction

GCM Solar + Volcanic patterns

Annual averagelate 17th vs late 18th Century Temperature change

Shindell et al, 2002 (submitted)

Boreholes

Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K., Keimig, F.T., Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data, Journal of Geophysical Research, 2002 (in press)

Greater trend?

Boreholes

Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K., Keimig, F.T., Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data, Journal of Geophysical Research, 2002 (in press)

Boreholes

Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K., Keimig, F.T., Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data, Journal of Geophysical Research, 2002 (in press)

Boreholes

Pattern Correlation

r=0.1 to 0.2

(depending on weighting of gridpoints)

Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K., Keimig, F.T., Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data, Journal of Geophysical Research, 2002 (in press)

BoreholesDetermine rotation in two-dimensional state space that yields optimal match with instrumental trend pattern

This rotation determines optimal projections of EOF patterns

Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K., Keimig, F.T., Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data, Journal of Geophysical Research, 2002 (in press)

Boreholes

Mann, M.E., Rutherford, S., Bradley, R.S., Hughes, M.K., Keimig, F.T., Optimal Surface Temperature Reconstructions Using Terrestrial Borehole Data, Journal of Geophysical Research, 2002 (in press)

CONCLUSIONS

•Comparisons between different proxy-based estimates, model predictions, and optimally-determined borehole estimates of past hemispheric temperature trends indicate broad consistency over the past millennium.

•Estimated and modeled patterns of surface temperature change during the “Little Ice Age” suggest the importance of both large-scale radiative responses and regional atmospheric dynamical response to both volcanic and solar forcing