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Entry: A Matter of Degrees Link: http://www.takimag.com/blogs/article/a_matter_of_degrees#16473 Post contents: Ian, Actually, the greenhouse people ignore the treeline evidence and try to argue the medieval warming out of existence. I have not seen them discuss (for example) Bryson's work on the treeline, and you might want to look at what Mann says about medieval warming. As to the current warming being exceptionally fast, the problem here is that the speed and magnitude of historical changes is difficult to gauge accurately -- i.e., we still do not know how warm the medieval warm period actually was. However, the current warming began in the middle of the 19th century, which means it has now lasted about 150 years. This may not be anything exceptional. The start of the late medieval cooling can arguably be dated to the massive, weather-caused harvest failures of 1315-1322. If we accept that the "little ice age" was fully developed by mid 16th century, then the cooling happened in somewhat over 200 years. (I emphasize the uncertaintly of the dates about the beginning and magnitude of the change. There is, for example, a record from England from 1257 complaining that the winter was so cold that all fig trees died!) As to the Antarctic evidence, the question here is, how much weight do you give to the satellite data, which now goes back 30 years? I agree there is contradictory data, and to me the satellite evidence looks like the most reliable there is. Thirty years of expanding ice are very diffifult to explain away, though we should not underestimate people's capabilities at sophistry. (Warming enthusiasts eagerly embrace the satellite obsevations from northern hemisphere.) An interesting detail: a recent hypothesis connects the warming to fluctuations in El Nino - La Nina, arguing that the latest increase in temperature is due to the prevalence of warm El Nino conditions since the mid 1970s. This year's large expansion in Antarctic ice agrees with this hypothesis, because we now have a cold La Nina in the Pacific. This is an intriguing possible connection, particularly since to my knowledge there is currently no explanation of what causes the El Nino - La Nina fluctuations. An English summary of the Green Alps evidence can be found at: http://www.spiegel.de/international/spiegel/0,1518,357366,00.html Sent at: 2009 01 08