Reducing carbon emissions supposedly will reverse warming, which is allegedly occurring even though, according to statistics published by the World Meteorological Organization, there has not been a warmer year on record than 1998.
As The New Republic's Jonathan Chait puts it, Will here shows his "unbelievable ignorance about global warming."
First of all, nobody says that reducing carbon emissions will "reverse" global warming. The point is merely to slow the process. This is pretty fundamental.
But the next part of Will's sentence is the key. Every serious person understands that 1998 was an outlier, because of El Nino, which raised temperatures. The fact that no year since then has been as hot does not in any way rebut the widespread consensus that the globe is warming.
Will can pretend not to understand this, but you'd think the Washington Post would be ashamed to keep printing this stuff.