On April 6, NASA and the National Snow and Ice Data Center (NSIDC) released new data on Arctic sea ice levels that further discredit a widely criticized February 15 column by George Will in which he falsely suggested that sea ice data undermine the scientific consensus that humans are causing global warming. The NASA/NSIDC press release stated that “the maximum [Arctic] sea ice extent for 2008-09, reached on Feb. 28, was 5.85 million square miles. That is 278,000 square miles less than the average extent for 1979 to 2000.” Reporting on the NASA/NSIDC findings, The Washington Post, which publishes Will's column, stated in an April 7 article that the data “provid[e] further evidence that the region is warming more rapidly than scientists had expected” and noted that the new data undermine Will's column.

Will's global warming columns have also recently been criticized by Washington Post editorial board member and cartoonist Tom Toles, Post weather columnist Andrew Freedman, and Post ombudsman Andrew Alexander.

In his February 15 column, Will wrote:

As global levels of sea ice declined last year, many experts said this was evidence of man-made global warming. Since September, however, the increase in sea ice has been the fastest change, either up or down, since 1979, when satellite record-keeping began. According to the University of Illinois' Arctic Climate Research Center, global sea ice levels now equal those of 1979.

Will's suggestion that the sea ice data he was citing undermined the case for human-caused global warming was false. The University of Illinois document that Will relied on in his February 15 column as purported evidence for his claim actually says that the University of Illinois data are consistent with global warming predictions. It says that "[i]n the context of climate change, GLOBAL sea ice area" -- which Will cited -- “may not be the most relevant indicator” and that it is important to distinguish between sea ice in the Northern and Southern hemispheres when discussing global warming. The document explains that "[a]lmost all" climate models project that human-caused global warming will result in decreased sea ice in the Northern Hemisphere, but that some recent studies have suggested that warming might initially cause the amount of sea ice to increase in the Southern Hemisphere, and that these projections are consistent with observed sea ice data. Even though Media Matters for America and others pointed out that the University of Illinois document actually contradicted the very point Will was purporting to make in citing it, Will falsely claimed in a February 27 column that he had “accurately reported” on the contents of the University of Illinois document.

Indeed, the NASA/NSIDC and University of Illinois data state that Arctic sea ice has decreased. The January University of Illinois document stated that “observed N. Hemisphere sea ice area is almost one million sq. km [386,102 square miles] below values seen in late 1979,” while the April 6 NASA release stated, "[T]he maximum [Arctic] sea ice extent for 2008-09, reached on Feb. 28, was 5.85 million square miles. That is 278,000 square miles less than the average extent for 1979 to 2000."

The NASA/NSIDC and University of Illinois data also noted a similar declining trend in Arctic sea ice thickness. The University of Illinois document stated:

Arctic summer sea ice is only one potential indicator of climate change, however, and we urge interested parties to consider the many variables and resources available when considering observed and model-projected climate change. For example, the ice that is presently in the Arctic Ocean is younger and thinner than the ice of the 1980s and 1990s. So Arctic ice volume is now below its long-term average by an even greater amount than is ice extent or area.

Likewise, the NASA/NSIDC release noted a decline in sea ice thickness since 2005:

Until recently, the majority of Arctic sea ice survived at least one summer and often several. But things have changed dramatically, according to a team of University of Colorado, Boulder, scientists led by Charles Fowler. Thin seasonal ice -- ice that melts and re-freezes every year -- makes up about 70 percent of the Arctic sea ice in wintertime, up from 40 to 50 percent in the 1980s and 1990s. Thicker ice, which survives two or more years, now comprises just 10 percent of wintertime ice cover, down from 30 to 40 percent.

[...]

“Ice extent is an important measure of the health of the Arctic, but it only gives us a two-dimensional view of the ice cover,” said Walter Meier, research scientist at the center and the University of Colorado, Boulder. “Thickness is important, especially in the winter, because it is the best overall indicator of the health of the ice cover. As the ice cover in the Arctic grows thinner, it grows more vulnerable to melting in the summer.”

The Arctic ice cap grows each winter as the sun sets for several months and intense cold sets in. Some of that ice is naturally pushed out of the Arctic by winds, while much of it melts in place during summer. The thicker, older ice that survives one or more summers is more likely to persist through the next summer.

[...]

Using two years of data from NASA's Ice, Cloud, and land Elevation Satellite (ICESat), Kwok's team estimated thickness and volume of the Arctic Ocean ice cover for 2005 and 2006. They found that the average winter volume of Arctic sea ice contained enough water to fill Lake Michigan and Lake Superior combined.

The older, thicker sea ice is declining and is being replaced with newer, thinner ice that is more vulnerable to summer melt, according to Kwok. His team found that seasonal sea ice averages about 6 feet in thickness, while ice that had lasted through more than one summer averages about 9 feet, though it can grow much thicker in some locations near the coast.