Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature BY MIKE LOCKWOOD1,2,* AND CLAUS FROHLICH3�� 1Rutherford Appleton Laboratory, Chilton, Oxfordshire OX11 0QX, UK 2Space Environment Physics Group, School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK 3Physikalisch���Meteorologisches Observatorium Davos, World Radiation Center, 7260 Davos Dorf, Switzerland There is considerable evidence for solar influence on the Earth���s pre-industrial climate and the Sun may well have been a factor in post-industrial climate change in the first half of the last century. Here we show that over the past 20 years, all the trends in the Sun that could have had an influence on the Earth���s climate have been in the opposite direction to that required to explain the observed rise in global mean temperatures. Keywords: solar variability and climate solar���terrestrial physics anthropogenic climate change 1. Introduction A number of studies have indicated that solar variations had an effect on pre- industrial climate throughout the Holocene. These studies have been made in many parts of the world and employ a wide variety of palaeoclimate data (Davis & Shafer 1992 Jirikowic etal.1993 Davis1994 van Geel etal.1998 Yu& Ito1999 Bond etal. 2001 Neff etal.2001 Huetal.2003 Sarntheinetal.2003 Christla et al. 2004 Prasad et al. 2004 Wei & Wang 2004 Maasch et al. 2005 Mayewski et al. 2005 Wang et al. 2005a Bard & Frank 2006 Polissar et al. 2006). Some of the most interesting of these studies used data that are indicators of more than just local climatic conditions. For example, Bond et al. (2001) studied the average abundance of ice- rafted debris (IRD), as measured in the cores of ocean bed sediment throughout the middle and North Atlantic. IRD are glasses, grains and crystals that are gouged out by known glaciers, which are then carved off in icebergs and deposited in the sediment when and where the icebergs melt. The sediment is dated using microfossils found at the same level in the core. The abundances of this IRD are very sensitive indicators of currents, winds and temperatures throughout the North Atlantic and reveal high, and highly significant, correlations with both the 10Be and 14C cosmogenic isotopes. A second example has been obtained from Proc. R. Soc. A doi:10.1098/rspa.2007.1880 Published online *Author and address for correspondence: Rutherford Appleton Laboratory, Chilton, Oxfordshire OX11 0QX, UK (m.lockwood@rl.ac.uk). Received 4 April 2007 Accepted 25 May 2007 1 This journal is q 2007 The Royal Society

the deviation of the oxygen isotope ratio from a reference standard variation, d18O, as measured in stalagmites in Oman and China in two separate studies (Neff et al. 2001 Wang et al. 2005a). These studies reveal an exceptional correspondence with the cosmogenic isotopes on all time scales between decades and several thousand years. The d18O is, in each case, a proxy for local rainfall and reveals enhanced precipitation caused by small north���south migrations of the intertropical convergence zone. Large effects are seen because the latitudinal gradients around the sites are large. The fact that the effect is seen at widely spaced locations is evidence for coherent shifts in the latitude of the monsoon belt. These correlations of palaeoclimate indicators are found for both the 14C and 10Be cosmogenic isotopes. The 10Be is a spallation product of galactic cosmic rays hitting atmospheric O, N and Ar atoms the 14C is produced by thermal neutrons, generated by cosmic rays, interacting with N. However, their transport and deposition into the reservoirs where they are detected (for example, ancient tree trunks for 14C and ice sheets or ocean sediments in the case of 10Be) are vastly different in the two cases. As a result, we can discount the possibility that the isotope abundances in their respective reservoirs are similarly influenced by climate during their terrestrial life history because the transport and deposition of each is so different. Thus, it is concluded that the correlations are found for both isotopes owing to the one common denominator in their production, namely the incident cosmic ray flux. On the time scales of the variations seen (decades to several thousand years), the dominant cause of variation in cosmic ray fluxes is the Sun (Beer et al. 2006). Hence, these studies are strong indicators of an influence of solar variability on pre-industrial climate. The research discussed previously studied variations of pre-industrial climate on a huge range of timescales between 102 and 108 years. Recently, solar effects on climate on time scales of 100 years and less have also been detected, even extending into the era of fossil fuel burning. Both observations and general circulation models (GCMs) of the coupled ocean���atmosphere climate system have improved our understanding of the coupling mechanisms and the natural internal variability of the climate system, such that it is now becoming feasible to detect genuine solar forcing in climate records (Haigh 2003). The thermal capacity of the Earth���s oceans is large and this will tend to smooth out decadal- scale (and hence solar cycle) variations in global temperatures, but this is not true of centennial variations (Wigley & Raper 1990). There is considerable evidence for century-scale drifts in various solar outputs, in addition to the solar cycle variations (Lean et al. 1995 Lockwood et al. 1999 Solanki et al. 2001, 2004 Lockwood 2004, 2006 Beer et al. 2006 Rouillard et al. 2007). In order to evaluate the relative contribution of solar variability and anthropogenic greenhouse effects to climate change (and other important factors such as volcanoes and sulphate aerosol pollution), GCMs have become increasingly important. Detection��� attribution techniques (see the review by Ingram (2006)) use regression of the observed global spatial patterns of surface temperature change with those obtained from a GCM in response to various forcing inputs. These studies have detected a solar contribution to global temperature rise in the first half of the twentieth century: a contribution that implies some form of amplification of the solar radiative forcing variation (Cubasch et al. 1997 Stott et al. 2000, 2003 North & Wu 2001 Douglass & Clader 2002 Meehl et al. 2003 Ingram 2006). M. Lockwood and C. Frohlich�� 2 Proc. R. Soc. A