DYNAMICAL MECHANISMS OF SOLAR CLIMATE FORCING IN PAST CENTURIES Department of Environmental Sciences, University of Virginia, Charlottesville, VA SORCE Meeting on Decadal Variability in the Sun and Climate Meredith, NH Oct 28, 2004 Collaborators: B. Adams, C. Ammann, R. Bradley; J. Brigham-Grette; M. Cane; A. Clement, T. Delworth; M.K. Hughes; T. Osborn; P. Jones, T. Rittennour, S. Rutherford; G. Schmidt; D. Shindell; S. Zebiak, Z. Zhang Michael E. Mann

Evidence for Solar Periodicities –The Instrumental Record –Long-term proxy data and proxy-based reconstructions Model/data comparisons DYNAMICAL MECHANISMS OF SOLAR CLIMATE FORCING IN PAST CENTURIES

Bidecadal Variability in North American Atmospheric Circulation and Drought During the 20 th century? Zhang, Z., Mann, M.E., Coupled Patterns of Spatiotemporal Variability in Northern Hemisphere Sea Level Pressure and Conterminous U.S. Drought, Journal of Geophysical Research, in press, yr

Bidecadal Variability in North American Atmospheric Circulation and Drought During the 20 th century? Zhang, Z., Mann, M.E., Coupled Patterns of Spatiotemporal Variability in Northern Hemisphere Sea Level Pressure and Conterminous U.S. Drought, Journal of Geophysical Research, in press, 2004

Bidecadal Variability in North American Atmospheric Circulation and Drought Prior to the 20 th century?

The existence of a bi-decadal (~20 years) drought rhythm in the western USA has been documented in instrumental drought records covering the past 100+ years, and its longer-term existence has been demonstrated as well in long tree- ring reconstructions of past drought extending back to AD This mode of variability is strongly related to forcing by the 22-yr Hale solar magnetic cycle and the 18.6-yr lunar nodal tidal cycle (Cook et al., 1997), an interaction that modulates the overall bi-decadal drought rhythm at centennial timescales. A new drought area reconstruction for the western USA now extends back to AD 800. This development has provided an opportunity for a much longer evaluation of solar and lunar tidal forcing to be made then was previously possible. In so doing, the results strongly show that solar and lunar tidal forcing have jointly influenced bi-decadal drought formation in the western USA for the past 1200 years and probably much farther back in time. In addition, the long tree-ring-based drought area reconstruction provides evidence for multi- centennial drought variability that might indicate longer-term solar forcing as well. This new information is described and compared to indicators of long-term solar variability in 14C and 10Be records. Overall, the results of this study provide compelling long-term statistical evidence for solar forcing of drought in the western USA. The challenge now is to understand the physics behind such forcing so that it can be properly modeled. Solar Forcing and the Western US Bi-Decadal Drought Rhythm: An Analysis Back to AD 800 Author: Edward R. Cook Affiliation: Lamont-Doherty Earth Observatory (SORCE ’03!)

Raw Varve Thickness Rittenour, T., Brigham-Grette, J., Mann, M.E., El Niño-like Climate Teleconnections in North America During the Late Pleistocene: Insights From a New England Glacial Varve Chronology, Science, 288, , Transformed Varve Thickness Processed (filtered and standardized) Varve Thickness New England Glacial Varves Bidecadal Variability in North American Prior to 20 th century?

Raw Varve Thickness Rittenour, T., Brigham-Grette, J., Mann, M.E., El Niño-like Climate Teleconnections in North America During the Late Pleistocene: Insights From a New England Glacial Varve Chronology, Science, 288, , Transformed Varve Thickness Processed (filtered and standardized) Varve Thickness Bidecadal Variability in North American Prior to 20 th century? New England Glacial Varves Power Spectrum (multitaper method)

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

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

Sensitivity in year band Proxy-based Temperature Reconstructions in Past Centuries

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, , 2001.

Proxy based reconstruction GCM Solar + Volcanic patterns Annual average late 17th vs late 18th Century Temperature change Shindell, D.T., Schmidt, G.A., Miller, R., Mann, M.E., Volcanic and Solar forcing of Climate Change During the Pre-Industrial era, Journal of Climate, 16, , 2003.

Decadally-smoothed Mann et al NINO3 (x-1) Jones et al, Science, 2001 Solar Forcing of El Nino? Verschuren et al, Nature, 403, , 2000.

Adams, J.B., Mann, M.E., Ammann, C.M., Proxy evidence for an El Nino-like Response to Volcanic Forcing, Nature, 426, , Volcanic Forcing of El Nino?

Cane, M.A., A.C. Clement, A. Kaplan, Y. Kushnir, D. Pozdnyakov, R. Seager, S.E. Zebiak, and R. Murtugudde, Twentieth-Century Sea Surface Temperature Trends, Science, 275, , Theoretical mechanism for natural radiative forcing of El Nino

Composite Nino3 (100 realizations of CZ model) Theoretical mechanism for natural radiative forcing of El Nino Response to Volcanic Forcing Tropical Volcanic radiative forcing (0.1 x W/m 2 ) Mann, M.E., Cane, M.A., Zebiak, S.E., Clement, A., Volcanic and Solar Forcing of the Tropical Pacific Over the Past 1000 Years, Journal of Climate, in press, 2004.

Tropical volcanic radiative forcing (0.1 x W/m2) Theoretical mechanism for natural radiative forcing of El Nino Superposed Epoch Analysis AD all (7) tropical events exceeding -2 W/m2 Superposed Epoch Analysis AD All (7) tropical events exceeding -4 W/m2 Mann, M.E., Cane, M.A., Zebiak, S.E., Clement, A., Volcanic and Solar Forcing of the Tropical Pacific Over the Past 1000 Years, Journal of Climate, in press, 2004.

Theoretical mechanism for natural radiative forcing of El Nino Combined response to Solar +Volcanic Forcing Ensemble mean Nino3 (100 realizations of CZ model) 40 year smooth Palymra coral isotopes (standardized to have same mean and standard deviation as Nino3 composite series) Mann, M.E., Cane, M.A., Zebiak, S.E., Clement, A., Volcanic and Solar Forcing of the Tropical Pacific Over the Past 1000 Years, Journal of Climate, in press, 2004.

Theoretical mechanism for natural radiative forcing of El Nino

Courtesy of E.Cook Theoretical mechanism for natural radiative forcing of El Nino

CONCLUSIONS Proxy-based climate reconstructions suggest persistent decadal and multidecadal relationships with solar forcing over centuries and millennia Forced changes in large-scale atmospheric circulation such as the NAO, and internal dynamics related to El Nino, may play an important role in explaining regional patterns of response to solar forcing Evidence exists for decadal timescale periodicities in instrumental and proxy climate records that may be related to solar forcing Decadal timescale signals suggest both thermodynamic and dynamical responses of the climate to solar radiative forcing.

Mann, M.E., Ammann, C., Bradley, R.S., Briffa, K., Crowley, T.J., Hughes, M.K., Jones, P.D., Oppenheimer, M., Osborn, T.J., Overpeck, J.T., Rutherford, S., Trenberth, K.E., Wigley, T.M.L., On Past Temperatures and Anomalous late 20th Century Warmth, Eos, 84, , 2003 [MODIFIED: RECONSTRUCTIONS ONLY; Boreholes—Rutherford and Mann (2004); Crowley & Lowery (updated)] Proxy-based Temperature Reconstructions in Past Centuries

Estimating Sensitivity from Model/Data comparisons 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, , Proxy-based Temperature Reconstructions in Past Centuries

Sensitivity on timescales > 40 year Proxy-based Temperature Reconstructions in Past Centuries 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, , AB CD

Mann, M.E., Lall, U., Saltzman, B., Decadal-to-century scale climate variability: Insights into the Rise and Fall of the Great Salt Lake, Geophysical Research Letters, 22, , 1995 Decadal Variability in the Great Salt Lake Level During the 20 th Century

Mann, M.E., Lall, U., Saltzman, B., Decadal-to-century scale climate variability: Insights into the Rise and Fall of the Great Salt Lake, Geophysical Research Letters, 22, , 1995 Quasi-Decadal Variability in North American Atmospheric Circulation During the 20 th Century

Mann, M.E., Lall, U., Saltzman, B., Decadal-to-century scale climate variability: Insights into the Rise and Fall of the Great Salt Lake, Geophysical Research Letters, 22, , 1995 Quasi-Decadal Variability in North American Atmospheric Circulation During the 20 th Century

Mann, M.E., Lall, U., Saltzman, B., Decadal-to-century scale climate variability: Insights into the Rise and Fall of the Great Salt Lake, Geophysical Research Letters, 22, , 1995 Quasi-Decadal Variability in North American Atmospheric Circulation During the 20 th Century

Bidecadal Variability in North American Atmospheric Circulation and Drought During the 20 th century? Zhang, Z., Mann, M.E., Coupled Patterns of Spatiotemporal Variability in Northern Hemisphere Sea Level Pressure and Conterminous U.S. Drought, Journal of Geophysical Research, in press, 2004