A Wrinkle In Ice (or Not)

By Carl Zimmer | February 22, 2009 11:53 am

[Correction appended]

There’s been a wrinkle in the global warming fact-checking saga I’ve been following this week.

Just to recap–George Will wrote a column claiming that global warming’s a lot of hype. He made a number of misleading statements, including one that was rejected by the very scientists he claimed as his source.

Will stated, “According to the University of Illinois’ Arctic Climate Research Center, global sea ice levels now equal those of 1979.”

A statement was then posted on the research center’s web site of the Polar Research Group:

We do not know where George Will is getting his information, but our data shows that on February 15, 1979, global sea ice area was 16.79 million sq. km and on February 15, 2009, global sea ice area was 15.45 million sq. km. Therefore, global sea ice levels are 1.34 million sq. km less in February 2009 than in February 1979. This decrease in sea ice area is roughly equal to the area of Texas, California, and Oklahoma combined.

A number of bloggers laid out the problems with the column and sought a response from the Washington Post. The Post announced that they had fact-checked Will’s column, and that it was just fine. I explained why that looks like some mighty poor fact-checking.

Last night in the comment thread, Doug drew my attention to an article on the ice record maintained by the US National Snow and Ice Data Center in Colorado (a different research center). On February 18 (three days after Will’s column appeared), the NSIDC announced that there was a glitch in the satellite sensors measuring ice in the Arctic, and so their record was gradually drifting off. The drift started in January, and gradually increased until they caught it in mid-February. The scientists now say that the latest estimates were off by 500,000 kilometers. They’re working now to compensate for the drift and correct the measurements. Here’s a graph from their web site.

The blue line marks the ice measurements taken by SSMI, the satellite NSIDC uses for the 30-year record of ice extent. The dashed red line is data from AMSR-E, a new  satellite that has also been measuring the ice and has remained accurate. The reason the scientists don’t switch over to the new AMSR-E satellite is that jumping from one data set to another can create the illusion of change that isn’t really there. But AMSR-E is still useful to the researchers, because they can compare its measurements to the ones they get using SSMI satellite to see if everything’s okay.

Some commenters wondered whether this development would cause me to take back my criticism. Let’s just set aside the fact that this news came out after Will had published his column, and thus could not have any real bearing on whether he or the Post bothered to contact the scientists that they cited as their source.

After looking at some of the web sites involved, I thought I ought to get in touch with the scientists who run the University of Illinois’ Arctic Climate Research Center–the center at the Polar Research Group–the scientists on whom Will depended for his claim, and which rejected that claim.

I got a prompt response from Bill Chapman, a University of Illinois climate scientist:

“It’s refreshing to have someone ask about the data before they write about it.”

Just pause to consider that. After all this kerfuffule–involving a nationally syndicated columnist, the assistants to that columnist, the editors at the columnist’s syndication service, the editors at the Washington Post editorial page, and the Post’s ombudsman–Chapman was refreshed that someone bothered to contact him about his research before writing about it. What a concept. For me, this whole affair has been about the value of fact-checking science, and Chapman’s reply shows just how little checking was carried out by the Post and company.

In his reply to me, Chapman explained that the two research centers, NSIDC and ACRC, both use the SSMI satellite readings, but they have different methods for building their time series. Chapman and his colleagues at ACRC use a composite of three sequential days for their ice cover readings. If a swath of data is missing on one particular day, they can go back to the previous day’s concentrations. If there are still missing regions, they go one more day back.

“Missing regions or swaths of data have always occurred from time to time in the SSMI record, which is why we set it up this way,” Champan explained.

Despite the recent trouble with the SSMI satellite, Chapman said the three-day-composites have still been meaningful. “As one check, we have been comparing our time series with those from the independent data source AMSR-E. They are just about identical so we are comfortable that our time series remain solid. Our time series and therefore the statement are unaffected by the recent satellite problems. If the sensor degrades a lot more, our numbers will be affected, but to date, they are not.”

I then asked what he thought about the Washington Post’s support of Will’s claim about ice. (To recap again, their support was decidedly roundabout. A January 1 post on a blog called Daily Tech claimed that global ice cover in late 2008 were unchanged from 1979. In response to that blog post, the Center posted a pdf on their web site explaining that “observed global sea ice area, defined here as a sum of N. Hemisphere and S. Hemisphere sea ice areas, is near or slightly lower than those observed in late 1979.” But then the scientists also explained that climate models predict a decline in Arctic ice, but are less certain about Antarctica, with some even suggesting an increase–making measurements of global sea ice not terribly relevant to the question of climate change. The Post ignored that part.)

Here’s Chapman’s reply:

Since their statements were based on the end of the previous year, and more importantly the end of 1979, the statement ‘global sea ice levels now equal those of 1979’ just didn’t make sense any more. We have received 80-100 emails from confused people who had read George’s column and looked up the graphs on the Cryosphere Today [one of the center’s web pages] and said they came to a different conclusion, or, could we point them to the report that said that Feb 1979 and Feb 2009 sea ice area was nearly the same. We had to post the current and corresponding 1979 values to avoid the inconsistency that readers were noting. After doing some googling, it appears that Daily Tech article got repeated on a lot of blogs, so it’s not surprising George Will came across it at some point. Still it was sloppy for them to not double check with the original source and it really points out the danger of making any conclusions on climate change based on any two days in history. I really wish they would have contacted us at some point to avoid this.

Our goal is to present the data in as concise and useful format as possible for interested users. Whether the Washington Post decides to publish a correction is up to them.


Finally, just to illustrate what Chapman’s talking about when he refers to the danger of picking out just two days in history, I thought I’d also include two graphs from Cryosphere Today. The top one shows the extent of Arctic sea ice, as compared to the 1978 to 2000 average. The bottom one is from Antarctica. A number of researchers have found a downward trend in the Arctic ice in recent decades, while there’s a small upward trend in the ice around Antarctica.artic600.jpgantarctic600.jpg

Correction: I erroneously called the University of Illinois Polar Research Group the University of Illinois Arctic Climate Research Center. The latter, used by George Will, is a fabrication. Details here.


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The Loom

A blog about life, past and future. Written by DISCOVER contributing editor and columnist Carl Zimmer.

About Carl Zimmer

Carl Zimmer writes about science regularly for The New York Times and magazines such as DISCOVER, which also hosts his blog, The LoomHe is the author of 12 books, the most recent of which is Science Ink: Tattoos of the Science Obsessed.


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