Breaking the ‘hockey stick’

It’s been a busy week for climate buffs and spin-meisters as the National Academy of Sciences released its eagerly awaited report on past climate change. Its origin is the scientific debate about the iconic “hockey stick,” the graph published by Michael Mann and colleagues that showed a smooth decline in temperature since A.D. 1000 with a sudden warming in the 20th century, presumably caused by burning of fossil fuels to generate the energy needed by our advanced civilization. Since thermometers were not available, the earlier data came from “proxies”: tree rings, ice cores, lake sediments, et cetera.

Global warming partisans, including some scientists and the Intergovernmental Panel on Climate Change, the U.N. science panel, embraced the hockey stick as “evidence” for greenhouse warming. This, even though the hockey stick denied the existence of natural climate fluctuations: the well-established Medieval Warm Period around A.D. 1000, when Vikings grew crops in Greenland, and the Little Ice Age, from about A.D. 1400 to A.D. 1850, when summer harvests failed and rivers and lakes froze over during severe winters.

Two Canadian researchers led the fight against the hockey stick, attacking both the data and statistical methodology. The battle soon spilled over into politics, with Rep. Joe Barton, Texas Republican, demanding that Mr. Mann reveal the details of his publicly funded work to permit other scientists to replicate his controversial results — a time-honored tradition in science. But Rep. Sherwood Boehlert, New York Republican, objected, partly on jurisdictional grounds, and asked the National Academy of Sciences to adjudicate.

Chaired by universally respected Texas A&M; professor Gerald North, the NAS panel has just released its diplomatically phrased report with all sides now claiming victory. The only firm conclusion is that it is warmer today than it was 400 years ago. The NAS panel might have stressed that A.D. 1600 is around the middle of the Little Ice Age. As Sen. James Inhofe, Oklahoma Republican and an outspoken opponent of warming scares, comments, it’s like comparing summer to winter to show a catastrophic temperature trend.

But now the fun begins. CNN reports in anxious tones that the Earth has got a “fever” — implying sickness. Really? Do we want a return to the severe climate of the LIA? The New York Times reports “warmest in 1,000 years,” but CNN and AP up this to 2,000 years.

In reality, the NAS report has re-established the LIA and MWP, and broken the hockey stick — although it never says so explicitly: “None of the reconstructions indicates that temperatures were warmer during medieval times than during the past few decades.” The report might have added that Northern Europe and Greenland were much warmer than today. But the statement “improving access to data on which published temperature reconstructions are based would boost confidence in the results” supports Mr. Barton and is a polite rebuke of Mr. Mann and coauthors for withholding data.

Altogether, a good report — if you accept its straight language and reject extrapolations.