Earth warmest in thousands of years? Controversy over new hockey stick

A few weeks ago, a major study was published in Science magazine reconstructing and charting the course of temperatures since the last ice age ended about 11,300 years ago.  It concluded the warmth of the last century was highly unusual in that historical context, generating attention-grabbing headlines.

Now critics claim the authors misled journalists in press materials and outreach by not emphasizing certain methodological details, while supporters say these details don’t affect the study’s implications.

To briefly summarize, the study “A Reconstruction of Regional and Global Temperature for the Past 11,300 Years” (Marcott et al., 2013), found:

* Temperatures warmed for about the first 1,000-2,000 years after the ice age ended
* Temperatures then leveled off until about 5,000 years ago
* From about 5,000 years ago into the 1800s, temperatures mostly cooled.

The study then compared its historic reconstruction of temperatures derived from mostly sediment and ice cores to the instrumental records (i.e. thermometers) of the last century. It concluded today’s temperatures are warmer than about 90 percent of the post-ice age period.

In chart form, the study’s temperature time series resembles a hockey stick with the historical data forming the stick’s downward-sloping shaft while the last 100 years constitute its blade, with an unmistakable increase.  The study effectively provides an extension of the famous hockey stick graph produced by Penn State climate researcher Michael Mann more than a decade ago.

When the study was released, the media uncorked a burst of articles with eye-popping headlines.  Mother Jones, for example, cautioned: “The Scariest Climate Change Graph Just Got Scarier” while the Atlantic warned: “We’re screwed: 11,000 years’ worth of ­climate data prove it.”

But critics charge combining the historic (reconstructed) and modern-day (thermometer) temperature record is deceptive and that the authors – both in conversations with journalists and  press materials – did not clearly communicate this (in their mind) questionable practice. And so, they say, the media overreached.

Specifically, Roger Pielke, Jr., a professor of environmental studies at University of Colorado, says the authors failed to make clear to reporters that their analysis did not provide new insight on modern temperature trends.

“…..the public representation of the paper was grossly in error,”  Pielke, Jr. blogs. “The [Marcott et al.] temperature reconstruction does not allow any conclusions to be made about the period after 1900.”

In a set of answers to frequently asked questions (FAQs) at the blog RealClimate.org, Marcott et al. point out that their study does not provide useful information on the hockey stick’s blade (20th century temperatures) :

“….the 20th century portion of our paleotemperature stack is not statistically robust, cannot be considered representative of global temperature changes, and therefore is not the basis of any of our conclusions,” Marcott et al. write.

This explanation and other information provided in the FAQs led the NY Times’ Andrew Revkin to ask: “how [do] the authors square the caveats they express [in the RealClimate.org FAQs] with some of the more definitive statements they made about their findings in news accounts [?]”

But Marcott et al. stress the modern temperature record relative to their historic reconstruction provides a legitimate basis for the conclusions trumpeted by the media:

“Our primary conclusions are based on a comparison of the longer term paleotemperature changes from our reconstruction with the well-documented temperature changes that have occurred over the last century…” Marcott et al. write.

Opinions vary on the soundness of comparing the datasets.  In an op-ed in the (Canada’s) Financial Post, economist Ross McKitrick rejects the practice.

“…you can’t just graft two completely different temperature series together and draw a conclusion from the fact that they look different,” McKitrick says.

But science blogger David Appell concludes the contrast between historic and modern data is the top issue on everyone’s mind, ripe for exploration.

“Should they have completely avoided any mention at all of how their results compare to what’s happening today?”, Appell writes. “Every reader in the world is going to want to know that, and who better to answer it than these scientists?”

Joe Romm, climate science and policy blogger at ClimateProgress.org, scoffs at the criticism related to use of the modern temperature record.

“What makes [the criticism] so anti-scientific is that the uptick [in temperatures] just happens to match the uptick in the heavily documented and independently verified instrumental record,” Romm writes.

. . .

Clarification, Wednesday, 5:20 p.m.: The following sentence was revised for clarification purposes: “Now critics claim the authors misled journalists in press materials and outreach by not emphasizing certain methodological details, while supporters say these details don’t affect the study’s implications.”

The originally published sentence said: “Now critics claim the authors misled journalists by omitting certain methodological details, while supporters say these details don’t affect the study’s implications.” This sentence was not clear that I was referring to press outreach rather than the substance of the paper, which – in fact – included the relevant methodological details. – Jason Samenow, author.

Jason is currently the Washington Post’s weather editor. A native Washingtonian, Jason has been a weather enthusiast since age 10.
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Jason Samenow · April 2, 2013