There is a new paper that examines (and forecasts) the role of solar forcing in climate system warming and cooling.
Lean, J. L., and D. H. Rind (2009): How Will Earth’s Surface Temperature Change in Future Decades?,
Geophys. Res. Lett., doi:10.1029/2009GL038932, in press. (accepted 9 July 2009).
the abstract reads
“Reliable forecasts of climate change in the immediate future are difficult, especially on regional scales, where natural climate variations may amplify or mitigate anthropogenic warming in ways that numerical models capture poorly. By decomposing recent observed surface temperatures into components associated with ENSO, volcanic and solar activity, and anthropogenic influences, we anticipate global and regional changes in the next two decades. From 2009 to 2014, projected rises in anthropogenic influences and solar irradiance will increase global surface temperature 0.15±0.03 C, at a rate 50% greater than predicted by IPCC. But as a result of declining solar activity in the subsequent five years, average temperature in 2019 is only 0.03±0.01 C warmer than in 2014. This lack of overall warming is analogous to the period from 2002 to 2008 when decreasing solar irradiance also countered much of the anthropogenic warming. We further illustrate how a major volcanic eruption and a super ENSO would modify our global and regional temperature projections.”
in their paper, with respect to their forecasts, they write
“The major assumption associated with our forecasts is that ‘past is prologue’; climate will continue to respond in the future to the same factors that have influenced it in the recent past and the response will continue to be linear over the next several decades.”
I have worked with Judith Lean and respect her scientific credentials. I respect also that she has placed her forecast in print and it is not for decades into the future, but is for a reasonably short enough time in the future to verify. I would have preferred, of course, that she use upper ocean heat content in Joules rather than the global surface temperature trend, which is a very poor metric to quantify regional and global warming and cooling (e.g. see). Nonetheless, all of us should follow the skill she achieves in the coming years.
Their new paper conflicts with the new paper which concludes that solar warming has been negligible since 1980.
Benestad, R. E., and G. A. Schmidt (2009), Solar trends and global warming, J. Geophys. Res., 114, D14101, doi:10.1029/ 2008JD011639.
whose abstract reads
“We use a suite of global climate model simulations for the 20th century to assess the contribution of solar forcing to the past trends in the global mean temperature. In particular, we examine how robust different published methodologies are at detecting and attributing solar-related climate change in the presence of intrinsic climate variability and multiple forcings. We demonstrate that naive application of linear analytical methods such as regression gives nonrobust results. We also demonstrate that the methodologies used by Scafetta and West (2005, 2006a, 2006b, 2007, 2008) are not robust to these same factors and that their error bars are significantly larger than reported. Our analysis shows that the most likely contribution from solar forcing a global warming is 7 ± 1% for the 20th century and is negligible for warming since 1980.”
The Benestad, R. E., and G. A. Schmidt 2009 and Lean, J. L., and D. H. Rind 2009 cannot both be correct in their conclusion regarding the magnitude of solar forcing on the Earth’s climate. They could both even be wrong based on such studies as
How Do Climate Models Work? by Roy Spencer
Compo,G.P., and P.D. Sardeshmukh, 2008: Oceanic influences on recent continental warming. Climate Dynamics.
with respect to the role of circulation changes in the magnitude of global warming and cooling.
Finally, both Benestad, R. E., and G. A. Schmidt 2009 and Lean, J. L., and D. H. Rind 2009 used the global average surface temperature trend to discuss the issue of global warming. They more appropriately should use the accumulation of Joules in the upper ocean as the diagnostic (e.g. see which the GISS group continues to ignore).