Six years ago, experts waited until after Katrina to start arguing over whether the hurricane was a consequence, at least in part, of global warming. This week, pundits didn't even wait for Irene to smash into the U.S. to start squabbling over the same question.

The green journalist-activist Bill McKibben, who last week was arrested in front of the White House while protesting an Obama administration proposal to build a new oil pipeline, got things started on Thursday. "Irene's got a middle name, and it's global warming," McKibben wrote in The Daily Beast. McKibben noted that last year was the warmest on record, and sea-surface temperatures along the East Coast of the U.S. are also at record highs—because of human-induced global warming.

This year, McKibben points out, we've already had "record floods from Pakistan to Queensland to the Mississippi basin; record drought from the steppes of Russia to the plains of Texas. Just about the only trauma we haven't had are hurricanes plowing into the U.S., but that's just luck—last year was a big storm year, but they all veered out to sea. This year we're already on letter I—which in a normal year we don't get to until well into October. Every kind of natural system is amped up, holding more power—about ¾ of a watt extra energy per square meter of the Earth's surface, thanks to the carbon we've poured into the atmosphere."

The journalist Michael Lemonick, writing at Climate Central, addressed the same issue from a slightly different and—I'm sure he thought—less objectionable angle. "Is this weather disaster caused by climate change?" Lemonick asked on Friday. "Wrong question," he replied. "Here's the right question: is climate change making this storm worse than it would have been otherwise? Answer: Absolutely."

Like McKibben, Lemonick points out that "sea-surface temperatures in the Atlantic Ocean are higher now than they used to be, thanks to global warming, and ocean heat is what gives hurricanes their power. All other things being equal, a warmer ocean means a more powerful storm."

Lemonick adds that "thanks largely to climate change, sea level is about 13 inches higher in the New York area than it was a century ago. The greatest damage from hurricanes comes not from high winds and torrential rains—although those do cause a lot of damage. It's from the storm surge, the tsunami-like wall of water a hurricane pushes ahead of it to crash onto the land. It was Hurricane Katrina's storm surge, not the wind or rain, that destroyed New Orleans back in 2005. With an extra foot of sea level to start with, in other words, Irene's storm surge is going to have a head start. And climate change is a big part of the reason why."

The backlash against McKibben and Lemonick was immediate, and it came not just from global-warming deniers, as one would expect, but from others concerned about climate change. The journalist Keith Kloor accuses McKibben of "rhetorical overkill" that undermines the legitimacy of the climate-change cause. The political scientist Roger Pielke Jr., commenting on Kloor's post, faults both McKibben and Lemonick for going "well beyond what the science can support."

So does the environmental reporter Andrew Revkin, author of the influential blog "Dot Earth." Depicting Irene as a harbinger of global warming-induced hurricanes striking the northeast United States with greater frequency "doesn't mesh with the science, which shows a measurable, though subtle, trend in the opposite direction." Revkin cites a 2008 study by the National Oceanic and Atmospheric Administration and University of Miami, "Global warming and United States landfalling hurricanes," which predicts that warming in the Atlantic produces more wind shear, which dissipates rather than intensifying storms.

There's something dispiriting about all these smart, well-intentioned people, who are all basically on the same side, squabbling among themselves in this way. I've faulted McKibben myself for rhetorical overkill—specifically, for suggesting that unchecked climate change may trigger wars and other forms of violence. But the comments of McKibben and Lemonick on Irene struck me as reasonable if debatable speculation, not as hyperbolic alarmism. Here's another question: When, if ever, will it be appropriate and responsible to link an extreme weather event such as Irene to anthropogenic climate change? And when that day comes, will making such a linkage be utterly moot?

Image courtesy Gannett Inc.