The exclusive focus on negative effects of global warming is perhaps most pronounced in the comments on health. But there are also positive affects from a slight warming of the planet. Bjorn Lomborg is a professor in the Business School of the University of Copenhagen and the author of The Sceptical Environmentalist. In his writings he points out that some global warming will increase the occurrence of diseases such as malaria but the number of deaths that are reduced globally is greater that those that are caused.The report discusses how global warming will melt the ice sheets in the polar regions and in Greenland. However, there is no mention that the Antarctic ice sheet is actually increasing. In Greenland some glaciers are declining but there is no mention that some are increasing.
The reports states that "Average Northern Hemisphere temperatures during the second half of the 20th century are very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1300 years (italics theirs)."
This is simply not true. The "hockey stick" chart showing the temperatures in the 20th century shooting up dramatically is often cited as proof of the dramatic rise in human caused global warming. But this rise in temperature has been a positive development because it finally signaled the final end to the "Little Ice Age" that cooled the earth for hundreds of years.
This was preceded by the extremely warm period of the middle ages which allowed crops to be grown in northern latitudes not possible previously and for the Vikings to establish permanent colonies on Greenland. When the Little Ice Age arrived all of this reversed. Viking colonies had to be abandoned and crops failed.
An analysis of the temperatures shows a rise in temperatures, signaling the end of the Little Ice Age, through about 1940. Since human industrial output was minimal during this period this warming could not have been caused by human activity. Then, from 1940 to 1970 temperatures fell again. Since the early 1970's temperatures have increased. However, it should be noted that some of the recent temperature increases cited by the IPCC contain spurious data that have not adequately corrected for urban "heat sinks". These data anomolies have been recently highlighted in peer reviewed scientific journals.
The statement by the IPCC report that our current temperatures are the highest in 500 years and probably the highest in 1300 years is probably based on temperature proxy analysis by Mann, et al., 1998. Mann's study attempted to reconstruct historical temperatures largely based on interpretation of tree rings. But further analysis of Mann's data determined that here were data errors. But the good news is that we do not need to rely on temperature proxies. There are direct means of reconstructing the historical temperatures.
The best of these direct means is the Greenland bore hole analysis. This analysis, published in the peer reviewed scientific journal Science (Dahl-Jenson et al. 1998 Science, 282, 268-271 "Past Temperatures Directly from the Greenland Ice Sheet". The Greenland bore hole analysis has been confirmed by a borehole reconstruction in the Ural Mountains published in Global and Planetary Change (Demeshko, D., V.A. Schapov, Global and Planetary Change, 2001)
The IPCC's statement that this is likely the highest temperature in 1300 years is simply not true. the A National Academy of Science review panel concluded in 2006 that the only conclusion that can be made is that the planet is warmer now that anytime in the last 400 years. Since this 400 year period concluded with the emergence from the Little Ice Age this is a very positive development.
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