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CLIMATE CHANGES DURING THE PAST MILLENNIUM Michael E. Mann Department of Environmental Sciences University of Virginia Gavin A. Schmidt and Drew T. Shindell.

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Presentation on theme: "CLIMATE CHANGES DURING THE PAST MILLENNIUM Michael E. Mann Department of Environmental Sciences University of Virginia Gavin A. Schmidt and Drew T. Shindell."— Presentation transcript:

1 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 Meeting December 2002

2 INSTRUMENTAL TEMPERATURE RECORD GLOBAL PROXY CLIMATE RECORDS Annual Resolution Proxy Climate Indicators Note: half of the surface area is between 30S and 30N

3 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.

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

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

6 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 Rings Greater variability?

7 Mid-Latitude Tree Rings 100012001400160018002000 Greater variability?

8 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.

9 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

10 Long-term climate response to volcanic eruptions: GISS GCM ensembles Pinatubo (12 years following eruption) Tambora (12 years following eruption) Time series (1959-1999) -0.4 -0.7 -1.2 -2.1 -0.4 -0.6 dT dF C W/m 2 Shindell et al, 2002 (submitted)

11 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

12 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.

13 Proxy based reconstruction GCM Solar + Volcanic patterns Annual average late 17th vs late 18th Century Temperature change Shindell et al, 2002 (submitted)

14 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?

15 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)

16 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)

17 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)

18 Boreholes Determine 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)

19 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)

20 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

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