Global Signatures of the “Little Ice Age” and “Medieval Climate Anomaly” and Plausible Dynamical Origins Michael E. Mann Penn State University with contributions from: Caspar Ammann, Raymond Bradley, Elizabeth Crespin, Jeff Donnelly, Greg Falugevi, Fangxing Fan, Hugues Goosse, Malcolm Hughes, Klaus Keller, Scott Rutherford, Drew Shindell, Axel Timmermann, Jonathan Woodruff, Zhihua Zhang 1th International Meeting on Statistical Climatology University of Edinburgh, Scotland July 13, 2010

Global Surface Temperature Changes

Climate “Proxy” Data… Global Surface Temperature Changes

Climate “Proxy” Data… Reconstructions of Past Climate

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

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

European Winter Cooling During the Little Ice Age

El Nino Sources of Uncertainty

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, 18, , How did Natural Forcings Influence influence ENSO and the Tropical Pacific During the Past Millennium?

simulation smoothed simulation result Coral isotope reconstruction of past El Nino variations Combined response to Solar +Volcanic Forcing ‘Little Ice Age’ wet in Kenya: El Nino-like conditions How did Natural Forcings Influence influence ENSO and the Tropical Pacific During the Past Millennium?

Cook et al, Science, ‘04 simulation smoothed simulation result Coral isotope reconstruction of past El Nino variations Combined response to Solar +Volcanic Forcing ‘Little Ice Age’ wet in southwestern U.S.: El Nino-like conditions How did Natural Forcings Influence influence ENSO and the Tropical Pacific During the Past Millennium?

Cook et al, Science, ‘04 simulation smoothed simulation result Coral isotope reconstruction of past El Nino variations Combined response to Solar +Volcanic Forcing ‘Medieval Warm Period’ dry in southwestern U.S.: La Nina-like conditions How did Natural Forcings Influence influence ENSO and the Tropical Pacific During the Past Millennium?

Surface Temperature Reconstructions

Science (11/27/09)

Regional Time Series Surface Temperature Reconstructions

statistical model historical record Model resolves ~50% annual variance in both calibration and split calibration/validation over Applications: Atlantic Tropical Cyclones

statistical model historical record Model resolves ~50% annual variance in both calibration and split calibration/validation over Applications: Atlantic Tropical Cyclones

sediments historical record 95% uncertainties Statistical model Applications: Atlantic Tropical Cyclones

Surface Temperature Reconstructions Science (11/27/09)

Surface Temperature Reconstructions Science (11/27/09)

Model-Data Comparisons Positive Phase of Northern Annual Mode Science (11/27/09)

Past Natural Arctic warming PROXIES MODEL Paleoclimate Data Assimilation

SAT Z(800mb) PROXIES MODEL Past Natural Arctic warming

CONCLUSIONS Reconstructed La Nina-like pattern during Medieval times, and El Nino- like anomalies during the “Little Ice Age”, suggest a ‘thermostat’ response response to natural radiative forcing Recent hemispheric-scale warmth anomalous in at least a millennial context; can only be explained by anthropogenic radiative forcing Prior to the 20 th century, warmth and cold was highly regionally variable Combination of warm tropical Atlantic and La Nina-like conditions in the tropical Pacific can explain periods of relatively high past Atlantic Hurricane activity Medieval warmth in high-latitude North Atlantic and parts of North America rivaled modern warmth Response of Northern Annular Mode/NAO to natural volcanic and solar radiative forcing appears to explain enhanced ‘Little Ice Age’ and ‘Medieval Warm Period’ temperature signal in regions such as Europe