Climate scientists are starting to face off again on thorny weather questions, as they did in aftermath of Hurricane Katrina.

Some climate scientists are actively exploring an issue climate activists may see as the Holy Grail of climate policy — the connections between extreme weather events and global warming.

Much of the interest started with Hurricane Katrina in 2005, which triggered a controversial debate among many in the climate community.

Similar attribution storms have since arisen over the 2010 Russian heat wave, the spate of deadly tornadoes that ripped through the Midwest in 2011, and now the unseasonably warm weather that blanketed large portions of the U.S. in March.

The latter event is proving as controversial and potentially as divisive to the climate community as Katrina was.

Kevin Trenberth, a senior scientist with the National Center for Atmospheric Research (NCAR), recently wrote in the journal Climatic Change:

The answer to the oft-asked question of whether an event is caused by climate change is that it is the wrong question. All weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.

Heidi Cullen, Climate Central’s chief climatologist, echoed this framing in an interview with the Daily Beast earlier in the week: “All weather is now born into an environment that is warmer and moister because of man-made greenhouse-gas pollution.”

In the interview, Cullen provided a sophisticated and elegant explanation for how the climate system works, comparing it to an “orchestra” and the way it produces many different sounds. But the interviewer’s focus was on understanding how global warming is affecting current extreme weather events. On this, Cullen offers an analogy that is also becoming a popular explanation: “Climate change stacks the deck for certain types of extreme weather events.”

How mainstream media and climate activists then translate all this involves a delicate dance. Consider this: A recent Yale University poll found that more Americans are increasingly linking the March heat wave and recent drought and tornado episodes of the past year to climate change.

Some press stories* on the poll’s findings interpret this development as a clear sign that the reality of global warming finally is starting to sink in with people.

Not surprisingly, Roger Pielke Jr., a University of Colorado climate policy scholar, asserted that such media coverage only reinforces a faulty understanding of the link between climate change and severe weather.

Regardless, as The New York Times article noted in its story on the Yale poll:

Advocacy groups seeking policies to limit climate change say that extreme weather is giving them an opening to reach the public.

A group called is planning a worldwide series of rallies on May 5, under the slogan “Connect the Dots,” to draw attention to the links between climate change and extreme weather.

But well-regarded Houston Chronicle science reporter Eric Berger cautions that it is problematic for activists to overly rely on the poll’s findings:

On one hand climate activists will welcome this report as it suggests the American public has found an aspect of climate change that concerns them. This has been a real challenge because the prospect of some nebulous, future warming has not galvanized the public nor their politicians to action.

On the other hand, attributing extreme weather to climate change is a bit like playing with fire.

A recent IPCC report on climate and extreme weather took a fairly moderate view, saying of losses due to climate change, “In many regions, the main drivers for future increases in economic losses due to some climate extremes will be socioeconomic in nature, (rather than climate extremes).”

Some climate scientists, fearing what they consider to be an over-play of the climate change/severe weather link, are pushing back. Cliff Mass, a University of Washington atmospheric scientist, recently wrote on his blog:

It is happening frequently lately. A major weather event occurs — perhaps a hurricane, heat wave, tornado outbreak, drought or snowstorm — and a chorus of activist groups or media folks either imply or explicitly suggest that the event is the result of human-caused (anthropogenic) global warming.

In a candid passage in that blog posting, Mass also implicates some in the climate science community for fostering this impression:

It is somewhat embarrassing for me to admit this, but part of the problem is that a small minority of my colleagues — people who should know better — are feeding the extreme-weather/climate hype in the mistaken belief that by doing so they can encourage people to do the right thing — lessen their carbon footprint.

John Mike Wallace, a National Academy of Sciences member and also a climate scientist at the University of Washington, struck a similar (but somewhat gentler) theme in a recent Los Angeles Times op-ed. He wrote that, “we must consider the possibility that the apparent weirdness of the weather in March isn’t all that weird if viewed in a larger historical context. In this respect, it’s noteworthy that large areas of the U.S. were just about as warm in March 1910 as they were in March 2012. With weather, weird things happen every now and again.” (Wallace’s “Forum” column in the American Geophysical Union’s EOS, of March 13, 2012, is also well worth reviewing. Andrew Revkin’s Dotearth blog has a useful examination of the issue and links to Wallace’s column (PDF) and more.)

Wallace leaves no doubt about his concerns over a warming climate: “If global warming continues as projected, the global consequences of deteriorating conditions in the tropics will soon be a lot more serious than a foretaste of summer weather in late winter.”

But in the politicized climate debate, activists (and perhaps also some of Wallace’s scientist colleagues) may regard some of his remarks as not very helpful.

If climate science is to remain the leading front in the battle over climate change, activists will have to allow time for the science to play out on the climate change/extreme weather connection. And that means we may soon see a full-throated debate within the climate science community along the lines of what occurred in the aftermath of Hurricane Katrina.

*The survey was conducted by a team led by Yale Forum Publisher and Director of the Yale Project on Climate Change Communication Anthony Leiserowitz (see Yale Forum article).

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