Which global warming ? A geophysicists politically incorrect look at climate change. Vincent Courtillot University Paris-Diderot and Institut de Physique du Globe de Paris Conference on Climate and Energy, Berlin Manhattan Institute, December 3rd, 2010 Sorbonne Paris Cité

Observations (1): a critical look at global and some regional temperature data…

Global mean temperature changes are small and not easy to determine with confidence

IPCC WG1 Fourth Assessment Report, 2007 Global temperature anomalies Continental means (decadal) blue = natural forcings pink = with anthropic forcings

Mean daily minimum temperature (°C) for 44 European meteorological stations (3yr running means)

Mean daily minimum temperature (°C) for 150 US meteorological stations (3yr running means)

Comparison between IPCC curves and our recalculated curves for Europe and the US IPCC WG1 Fourth Assessment Report, 2007 Le Mouël et al, 2008, 2009

An icon of global warming : Manns hockey stick curve

Mann Moberg

Tree ring width (TRW) and density (MXD) : a function of cambial age, hence a serious artefact Grudd, 2008

Recent global warming is often labeled as « abnormal » or « without precedent ». It actually had equivalents in 750, 1000, 1400 and 1750 and the two-century long period around 1000AD was warmer and longer than generally recognized… at least in Northern Europe Medieval climatic optimum Grudd, 2008 Grudd, 2002

Observations (2): our groups work in the past 5 years…

Decadal and longer-term (multi-decadal) changes in solar activity A summary of recent results

Decadal and longer-term (multi-decadal) changes in solar activity A summary of recent results

Correlation between solar activity and mean inter- annual quadratic variation (or lifetime) of temperature for Europe (left) and Holland (right). Le Mouël et al,

Time variations of the mean period of the MJO wave packet (MJO1 index), taken between 30–60 days (a) and 50–80 days (b). The difference between the two is compared to sunspot number (c) and mean quadratic variation of Z component in the Alibag magnetic observatory (d). (4 year running means) The Madden-Julian oscillation 2

Evidence of 11-yr cycle related modulation of the 6 month spectral peak in length-of-day (Earth rotation) amplitude phase Le Mouël et al, GRL, 2010b 3

Comparison to sunspot number (reversed in sign and with one-year phase lag) and to cosmic ray count (no sign or phase change) Le Mouël et al, GRL, 2010b 3

Which forcing factors ? Which forcing factors ?

Natural distribution of heat fluxes in the atmosphere

Clouds reflect about 80 Wm -2 (out of incoming 342 Wm -2 ) A 10% change in cloud cover in the 20th century would have led to a forcing of 8 Wm -2

Correlation between cosmic rays and low cloud cover Svensmark, 2007 High altitude Middle altitude Low altitude

Tinsley et Heelis, 1993 Accumulation of electric charges at the boundaries of layered clouds results from vertical current density Jz from the ionosphere to the surface. Charges attach to droplets and aerosols and alter cloud microphysics.

The « golden triangle » : - observation - physical mechanisms (« theory ») - numerical modeling A need for a falsifiable model (« checkable predictions ») The importance of uncertainties The « golden triangle » : - observation - physical mechanisms (« theory ») - numerical modeling A need for a falsifiable model (« checkable predictions ») The importance of uncertainties Conclusion (1):

Global warming ? Yes, over the past 150 years, but very irregular… Not without precedent in the past two thousand years … Complex and multiple sources, uncertainties insufficiently taken into account in models… Conclusion (2):

Conclusion (3): Growing evidence along several lines for significant influence of decadal to multi-decadal variations in solar activity on a number of climate related features, with an amplitude well beyond that expected for 1/1000 changes in total solar irradiance. Some of the effects we find have a relative amplitude in excess of 30% of the original signals. Mechanism likely involve cosmic rays and/or vertical currents in ionosphere and atmosphere, and clouds.

How expertise is gathered and advice built (the « consensus »): a risk for « anti-science » backfiring Other important problems running the risk of being considered as secundary : - the quest for drinking water - management of urban waste - hunger in the world … Geoscientists can be sources of solutions to several of these problems… How expertise is gathered and advice built (the « consensus »): a risk for « anti-science » backfiring Other important problems running the risk of being considered as secundary : - the quest for drinking water - management of urban waste - hunger in the world … Geoscientists can be sources of solutions to several of these problems… Conclusion (4) and discussion: