A breakthrough article this week in the science supplement of the very respectable newspaper NRC Handelsblad. The topic is global cooling, the investigator is Bas van Geel, palynologist (yes, I had to look it up too) at the equally respected University of Amsterdam and the suspect: the sun. Van Geel with colleagues investigated a well-known episode of global cooling called the Homeric minimum taking place around 850 BCE and reported about it in Nature Geoscience (DOI). They investigated the annually laminated sediments of Meerfelder Maar lake and measured among other things the concentration of beryllium-10 which was found to be especially high in this period. The production of this isotope is inversely related to the number of sunspots (high solar activity interferes with cosmic rays) and hence according to van Geel, the Homeric minimum results from a decline in solar activity. The newspaper article explains that the difference in total radiation between an active sun and an inactive sun is only 0.1% but that the variation in UV radiation is more relevant because it controls ozone levels which in turn control stratospheric temperatures. You are still with us?
Interestingly van Geel & team in their Nature report are reluctant to extrapolate their findings to the current global warming/cooling event but when it comes to the news media (the aforementioned NRC but also at least one other Dutch newspaper), van Geel is very opinionated: the IPCC underestimates the effect of solar radiation because it is more difficult to measure than things like carbon dioxide concentration or water vapor. For the last 10 years the planet refuses to warm up and not coincidentally the current solar maximum is meagre at best compared to the previous one.
But why this reluctance for an established hard-core scientist to state this hypothesis in a genuine article and instead turn to the news media to vent of steam? Fear of reputation damage? Intimidated by the opposition saying that it is a regional effect at best? Thus far the band of climate sceptics is composed of political activists, bloggers, and retired geologists. A contribution from an active main-stream scientist would be welcome. This blog is eagerly anticipating van Geel's next article. This sun/climate battle should be fought in the journals and not in the newspapers.