Constraining model transient climate response using independent observations of solar-cycle forcing and response

Abstract

The phenomenon of 11-year solar cycles has a well-measured forcing, and the response in surface temperature is confirmed using multiple datasets, including reanalysis (NCEP/NCAR and ERA-40) and blended in situ land-ocean data (GISS and HadCRUT3). Missing coverage in the historical in situ station data reduces the amplitude of the response compared to the geographically complete reanalysis data, but all extracted signals are statistically robust. A transient climate sensitivity parameter can be defined once forcing and response are known. The coupled atmosphere-ocean models participating in the 4th Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) span a large range in their transient climate response (TCR). Using observational results on the response to the 11-year solar variation, we derive a constraint for the TCR. It is seen that, compared with our derived constraint, most models assessed by IPCC AR4 have too low a TCR, even lower than that derived from the station data. Copyright 2008 by the American Geophysical Union.