Croker Sack

"Democracy is the theory that the common people know what they want, and deserve to get it good and hard." — Henry Louis Mencken (1880-1956)

Thursday, June 22, 2006

The Hockey Stick: Plausible or proven?

The National Academy of Sciences released a report on global climate change today that seems a little bit equivocal about the "hockey stick" graph of surface temperature changes, so how much of the report's actual findings will be emphasized by the news media?

Here is an excerpt from the NAS news release:

The report was requested by Congress after a controversy arose last year over surface temperature reconstructions published by climatologist Michael Mann and his colleagues in the late 1990s. The researchers concluded that the warming of the Northern Hemisphere in the last decades of the 20th century was unprecedented in the past thousand years. In particular, they concluded that the 1990s were the warmest decade, and 1998 the warmest year. Their graph depicting a rise in temperatures at the end of a long era became known as the "hockey stick."

The Research Council committee found the Mann team's conclusion that warming in the last few decades of the 20th century was unprecedented over the last thousand years to be plausible, but it had less confidence that the warming was unprecedented prior to 1600; fewer proxies -- in fewer locations -- provide temperatures for periods before then. Because of larger uncertainties in temperature reconstructions for decades and individual years, and because not all proxies record temperatures for such short timescales, even less confidence can be placed in the Mann team's conclusions about the 1990s, and 1998 in particular.

The committee noted that scientists' reconstructions of Northern Hemisphere surface temperatures for the past thousand years are generally consistent. The reconstructions show relatively warm conditions centered around the year 1000, and a relatively cold period, or "Little Ice Age," from roughly 1500 to 1850. The exact timing of warm episodes in the medieval period may have varied by region, and the magnitude and geographical extent of the warmth is uncertain, the committee said. None of the reconstructions indicates that temperatures were warmer during medieval times than during the past few decades, the committee added.

Note how the NAS characterized the "hockey stick" -- reconstructions from 1600 onward make it "plausible," but prior to 1600 there is less confidence in it; and there is even less confidence in the claim that the 1990s and 1998 in particular were the hottest years in the past 1000 years.

Try to find that lack of confidence in this Associated Press article published in the Seattle Post-Intelligencer:

Thursday, June 22, 2006 · Last updated 8:16 p.m. PT

Earth hottest it's been in 2,000 years


WASHINGTON -- The Earth is running a slight fever from greenhouse gases, after enjoying relatively stable temperatures for 2,000 years. The National Academy of Sciences, after reconstructing global average surface temperatures for the past two millennia, said Thursday the data are "additional supporting evidence ... that human activities are responsible for much of the recent warming."
Combining that information gave the panel "a high level of confidence that the last few decades of the 20th century were warmer than any comparable period in the last 400 years," the panel wrote. It said the "recent warmth is unprecedented for at least the last 400 years and potentially the last several millennia," though it was relatively warm around the year 1000 followed by a "Little Ice Age" from about 1500 to 1850.

Their conclusions were meant to address, and they lent credibility to, a well-known graphic among climate researchers - a "hockey-stick" chart that climate scientists Michael Mann, Raymond Bradley and Malcolm Hughes created in the late 1990s to show the Northern Hemisphere was the warmest it has been in 2,000 years.

I don't believe the NAS press release and the AP story say the same thing.

I look forward to reading the entire NAS report, but I don't look forward to seeing it used by the global-warming propagandists.


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