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Solar Forcing of Little Ice Age Climate
Shindell, D.T., Schmidt, G.A., Mann, M.E., Rind, D. and Waple, A. 2001. Solar forcing of regional climate change during the Maunder Minimum. Science 294: 2149-2152.

What was done
The authors used a version of the Goddard Institute for Space Studies GCM - which includes a detailed representation of the stratosphere and parameterizations of the response of ozone to solar irradiance, temperature and circulation changes - to estimate climatic differences between the period of the Maunder Minimum in solar irradiance (mid-1600s to early 1700s) and a century later, when solar output was relatively high for several decades.

What was learned
For the globe as a whole, the authors reported a mean annual near-surface air temperature difference on the order of 0.3 to 0.4C between the model-simulated climates of the two periods, which they say is about the magnitude of change suggested by historical and proxy climate data. Much larger temperature differences between the two periods (on the order of 1 to 2C) were observed in model reconstructions for only Northern Hemispheric continents in winter; but similar differences were also observed in the historical and proxy climate records of those regions.

What it means
Although the GCM employed in this study was by no means perfect (none are) and omitted several phenomena believed to be of importance to correctly simulating earth's climate, such as changes in ocean circulation, the authors say their results "provide evidence that relatively small solar forcing may play a significant role in century-scale Northern Hemisphere winter climate change," specifically stating that "colder winter temperatures over the Northern Hemispheric continents during portions of the 15th through the 17th centuries (sometimes called the Little Ice Age) and warmer temperatures during the 12th through 14th centuries (the putative Medieval Warm Period) may have been influenced by long-term solar variations."

We certainly agree that variable solar irradiance may have played the role Shindell et al. ascribe to it. One must be cautious, however, in citing the results of this exercise as evidence for the validity of the solar radiation effect, for the same climate model also predicts significant CO2-induced global warming over the latter part of the past century, as well as into the future. It is important to realize that the right answer can be obtained by both right and wrong means; and we don't believe this model yet does everything right. Omitting changes in the circulation of the world's oceans, for example, is not a trivial matter.