This is a teeny tiny point. It appears that he changed a column in a way that made it a tiny bit more difficult for readers to check something for themselves.
Brad DeLong quoted him as writing
The editors who checked the Arctic Research Climate Center Web site believe it did not, on balance, run counter to Will's assertion that global sea ice levels "now equal those of 1979." I reviewed the same Web citation http://arctic.atmos.uiuc.edu/cryosphere/global.sea.ice.area.pdf and reached a different conclusion.
Now the column reads
The editors who checked the Arctic Research Climate Center Web site believe it did not, on balance, run counter to Will's assertion that global sea ice levels "now equal those of 1979." I reviewed the same Web citation and reached a different conclusion.
The url is not presented after the word "citation." Actually I guess Brad could have added the url (he's too busy right now to answer if I ask). The column doesn't contain the url. It does contain a link to the University of Illinois Arctic Climate Research Center home page.
Brad DeLong is not the only person who has expressed the suspicion that Alexander wrote his first piece defending Will without clicking the link. I too have that suspicion. It seems possible to me that after reading the pdf, Alexander decided that it contradicted Will's claim. It seems possible that after putting the link into his column, he decided to make it a bit more difficult for readers to check for themselves, because his earlier interpretation and that of "editors" is so absurd.
Not that it matters much.
In Will's second column he acknowledges that the source of his contested claim was not the University of Illinois Arctic Climate Research Center (UIACRC) but rather a blog.
He wrote "Citing data from the University of Illinois' Arctic Climate Research Center, as interpreted on Jan. 1 by Daily Tech, a technology and science news blog, the column said that since September"
Without noting that this confession implies that he committed a gross journalistic error in his first column when he wrote "According to the University of Illinois' Arctic Climate Research Center, global sea ice levels now equal those of 1979."
He says the claim about the UIACRC in a blog justifies his asserting the claim as fact. The claim is not just that "global sea ice levels now equal those of 1979" (which is false) but also that the UIACRC said or wrote that they are. The correct sentence would read "According to the blog Daily Tech, a technology and science news blog, the UIACRC found that global sea ice levels now equal those of 1979." The UIACRC officially denies that they found, or reported or said or wrote any such thing. Will made a claim of fact about the UIACRC based on a blog and didn't say he was assuming that what he read on some blog must be true.
In his second column printed Feb 27he wrote "The center generally does not make its statistics available, but in a Jan. 12 statement the center confirmed that global sea ice levels were within a difference of less than 3 percent of the 1980 level."
As if it confirmed his claim that "According to the University of Illinois' Arctic Climate Research Center, global sea ice levels now equal those of 1979".
Then astonishingly Will wrote in his Feb 27 column.
"So the column accurately reported what the center had reported. "
Huh ? -2% = 0 ??? That's a good bit of reduction in ice in 29 years. If he had described the area in multiples of say the size of Delaware (or California for that matter) even he wouldn't have the nerve to call that confirmation.
Also importantly Will didn't claim that he knew about the Jan 12 statement (presumably the pdf) when he wrote his original column, that is he confesses that he operated on the assumption that, if something is written on a blog it must be true and can be stated in his own voice as fact.
Obviously George Will thinks mere facts are beneath him. Alarmingly Fred Hiatt seems to agree that mere facts are beneath George Will.