Confusion Over The 20th Century Warming Trend

There appears to be a great deal of confusion concerning the warming trend since 1850, and its relation to AGW theory. The scientific community accepts most of this warming as natural. And I stress MOST of this warming, because climatologists can still argue that SOME of this warming trend (1944-2000) is man-made, however, it indistinguishable from the natural fluctuations in the climate system itself. It is also worth considering this: we are still recovering from the Little Ice Age of the 1700s, which is probably colouring our view of the late 20th century warming, which may or may not be partly anthropogenic.

Furthermore, the 20th century shows a pattern of warming early on in the century, which cannot be related to the increase of so-called greenhouse gases (GHGs) in the atmosphere. This is because most of the GHGs from human activity have been put in the air in the latter half of the 20th century. (A century that can essentially be divided in half between what we know is natural and what is supposedly anthropogenic.) It is important to note that the IPCC III-IV assessment reports do not dispute this—they accept it. It is curious that this is not well known by those who support AGW theory.

AGW proponents (including Mann, Jones, Hansen etc.) accept that up until 1944, or thereabouts, there was warming, unrelated to man-made emissions. Then up until 1977 there was cooling, or a flattening of the temperature, but this pattern of warming-cooling CANNOT be from carbon dioxide. Then, finally, there was the warming at the end of the 20th century. The reality is that you cannot look at the 20th century and say that all this warming MUST be from man-made GHGs; only that the warming from the last part of the twentieth century MIGHT be from greenhouse gases. As things stand, it is speculation, not fact that the recent global warming must be caused by human activities.

The pattern suggests that the world has entered a period of slight cooling until about 2030:

1882 – 1910 Cooling
1910 – 1944 Warming
1944 – 1977 Cooling
1977 – 2001 Warming

31 July, 2010

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