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OT: Moorabal/Lal Lal wind farm 6-Jun-2009 At 7:06:20 AM TonyB

Message

>On 5/06/2009 evanbb wrote:
>>>Firstly here's a graph from the IPCC. It shows how temperatures were
>>>much higher than currently during the Medieval warm Period.
>>Now, I know this is a harsh term, but I think you're pulling a furphy
>>here. That graph is not from the IPCC.

Calling me a liar is offensive. Here's an actual quote from IPCC 1990, together with the actual Figure 7.1 from the IPCC 1990 report.

Note especially : "Thus some of the global warming since 1850 could be a recovery from the Little Ice Age rather than a direct result of human activities."

An apology would be appropriate.

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"
There is growing evidence that worldwide temperatures were higher than at present during the mid-Holocene (especially 5,000-6,000 BP) at least in summer, though carbon dioxide levels appear to have been quite similar to those of the pre-industrial era at this time (Section 1). Thus parts of western Europe, China, Japan, the eastern U.S.A. were a few degrees warmer in July during the mid-Holocene than in recent decades (Yoshino and Urushibaru, 1978; Webb et al 1987; Huntley and Prentice, 1988; Zhang and Wang, 1990). Parts of Australasia and Chile were also warmer. The late tenth to early thirteenth centuries (about AD950-1250) appear to have been exceptionally warm in western Europe, Iceland and Greenland (Alexandre 1987; Lamb, 1988). This period is known as the Medieval Climatic Optimum. China was, however, cold at this time (mainly in winter) but south Japan was warm (Yoshino 1978). This period of widespread warmth is notable in that there is no evidence that it was accompanied by an increase of greenhouse gases. Cooler episodes have been associated with glacial advances in alpine regions of the world such neo-glacial episodes have been increasingly common in the past few thousand years.

Of particular interest is the most recent cold event, the Little Ice Age which resulted in extensive glacial advances in almost all alpine regions of the world between 150 and 450 years ago (Grove 1988) so that glaciers were more extensive 100-200 years ago than now nearly everywhere (Figure 7.2) Although not a period of continuously cold climate, the Little Ice Age was probably the coolest and most globally extensive cool period since the Younger Dryas. In a few regions, alpine glaciers advanced down-valley even further than during the last glaciation (Miller, 1976). Some have argued that an increase in explosive volcanism was responsible for the coolness (for example Hammer 1977; Porter 1986); other claim a connection between glacier advances and reductions in solar activity (Wigley and Kelly, 1989) such as the Maunder and Sporer solar activity minima (Eddy, 1976) but see also Pittock (1983).

At present there is no agreed explanation for these recurrent cooler episodes. The Little Ice age came to an end only in the nineteenth century. Thus some of the global warming since 1850 could be a recovery from the Little Ice Age rather than a direct result of human activities. So it is important to recognize that natural variations of climate are appreciate and will modulate any future changes induced by man.

Schematic diagrams of global temperature variations since the Pleistocene on three time-scales: (a) the last million years; (b) the last ten thousand years, and (c) the last thousand years. The dotted line nominally represents conditions near the beginning of the twentieth century.
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