Tuesday, May 22, 2007

Another Scientific Paper About Solar Cycle Impact on Temperatures

N. Scafetta and B.J. West, "Phenomenological solar signature in 400 years of reconstructed Northern Hemisphere temperature record." Geophysical Research Letters (2006)
. This paper examines how well various Total Solar Irradiance (TSI) measures map to temperature records for the Northern Hemisphere. Not surprisingly, the TSI and temperature data are really only good data for a short period, but there are a number of proxies for both. I am not surprised to find that one of the proofs of a decline in solar output in the Little Ice Age is by looking at carbon-14 production. Carbon-14 production is caused by cosmic ray flux--and as solar output increases, cosmic rays have a harder time reaching the Earth's atmosphere.

Anyway, the paper points out what a lot of people know: temperatures in the Northern Hemisphere during the medieval maximum (about 1000-1100 AD) were roughly the same as temperatures in the period 1961-1990. They were about 0.7 degrees Kelvin (the same as Celsius for those of us who think that oxygen is a gas, not a solid) lower during the Maunder Minimum (1645-1715) (when sunspot activity effectively ceased) and about 0.6 degrees lower during the Dalton Minimum (1795-1825). And guess what? The TSI proxies match very well with these temperature changes.

The authors don't claim that all of the current global warming is solar:
Since the 17th century minimum the sun has induced a warming of [approximately] 0.7K. This warming is of the same magnitude of the cooling of [delta]T [approx.] 0.7K from the medieval maximum to the 17th century minimum. Because anthropogenic
contributions to climate change are unlikely before 1800-1900 AD, this finding suggests the presence of a millenarian solar cycle, with two medieval and contemporary maxima, driving the climate of the last millennium [Eddy, 1976].
They do make the claim that TSI proxies suggest that about 50% of the current global warming can be explained as direct and indirect consequences of solar output changes.

What is really fascinating about reading papers like this is the gap between the AGW fanatics and their claims that the science is settled, and actually reading scientific papers on the subject. The environmentalists have to lie about this, of course, because the alternative is to admit that there's a lot of evidence that we are only part of this--and we don't even know how much. The paper points out that there are a lot of other natural feedbacks involving carbon dioxide--and these aren't well understood.

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