Sean Kirst asks whether the recent annual recurrence of January thaws is a sign of global warming or simply part of the natural variability of our upstate winters. The answer is both: as a singular event a warm winter spell or even a entire warm winter season is not outside the realm of natural variability. But looking at seasonal trends in the aggregate, anthropogenic global warming suggests that statistically, Northeast winters should experience an increase in extreme warming events. This is especially the case when additional warming factors such as El Nino are in play; this point was made in detail at Real Climate in response to last year’s anomalous winter:
...one cannot attribute a specific meteorological event, an anomalous season, or even…two anomalous seasons in a row, to climate change…But one can argue that the pattern of anomalous winter warmth seen last year, and so far this year, is in the direction of what the models predict.
In reality, the individual roles of deterministic factors such as El Nino, anthropogenic climate change, and of purely random factors (i.e. “weather”) in the pattern observed thus far this winter cannot even in principle be ascertained. What we do know, however, is that both anthropogenic climate change and El Nino favor, in a statistical sense, warmer winters over large parts of the U.S. When these factors act constructively, as is the case this winter, warmer temperatures are certainly more likely. Both factors also favor warmer global mean surface temperatures (the warming is one or two tenths of a degree C for a moderate to strong El Nino)....
These statements hold up for this year as well. This is a critical point to understand about anthropogenic global warming because it underscores the complexity of the climate system and impossibility of ascribing specific weather events to climate change even though the general trends and basic physics are absolutely on solid ground forming the basis of the scientific consensus on global warming. And it is the isolated uncertainty of singular climate phenomenon that global warming contrarians have been most successful at exploiting. But it is also environmental advocates that contribute to this misunderstanding when they too cherry pick extreme weather events to promote action on global warming – whether a January thaw or Hurricane Katrina (as Gore famously did in “An Inconvenient Truth”).
Coincidentally I’ve just began reading “Storm World” which documents the scientific controversy surrounding global warming and hurricane prediction. The author, Chris Mooney, recently commented on his disappointment “with the way that some environmental advocates indefensibly exploit individual events to make a case about global warming.” But at the same time he stresses:
When it comes to wildfires, or hurricanes, or droughts, or many other weather related phenomena [like a January thaw], there is strong published research suggesting that global warming ought to be changing these events in some way in the aggregate, even if we can’t detect such changes in any individual occurrence (for basic statistical reasons). This research makes it more than fair to at least raise the subject of climate change when such events occur — with the appropriate caveats, of course.