In an article by The Huffington Post’s Tom Zeller, Jr., Trenberth said that storms like Sandy are the “new normal,” but that’s not exactly how the Intergovernmental Panel on Climate Change (IPCC), the world’s foremost authority on the subject, sees it. In a special report on extreme weather published this summer, it said:
There is low confidence in any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity (i.e., intensity, frequency, duration), after accounting for past changes in observing capabilities.
That’s not to say that events like Sandy won’t become the new normal eventually. According to the special report, there’s already been an increase in the number of heavy precipitation events in some regions. There’s also been a decrease in some regions, but it’s “likely” that there are more in the former category, and “there is medium confidence that anthropogenic influences have contributed to intensification of extreme precipitation at the global scale.” As for the future (and it’s important to note that the IPCC distinguishes between heavy rainfall events and hurricanes, which are related but distinct):
It is likely that the frequency of heavy precipitation or the proportion of total rainfall from heavy falls will increase in the 21st century over many areas of the globe. This is particularly the case in the high latitudes and tropical regions, and in winter in the northern mid-latitudes. Heavy rainfalls associated with tropical cyclones are likely to increase with continued warming. There is medium confidence that, in some regions, increases in heavy precipitation will occur despite projected decreases in total precipitation in those regions.
Average tropical cyclone maximum wind speed is likely to increase, although increases may not occur in all ocean basins. It is likely that the global frequency of tropical cyclones will either decrease or remain essentially unchanged.
There is medium confidence that there will be a reduction in the number of extratropical cyclones averaged over each hemisphere. While there is low confidence in the detailed geographical projections of extratropical cyclone activity, there is medium confidence in a projected poleward shift of extratropical storm tracks.
That’s a lot to chew on, obviously, but the point is that reporters who generalize about climate change and extremes do so at their own peril, as do those who seek easy answers about any individual weather event. Boing Boing’s Maggie Koerth-Baker described the situation perfectly in her post about Sandy:
Part of the problem here is that we’re expecting science to operate on the scale of American media news cycles, which doesn’t really work. We want to talk about this while the storm is raging or, barring that, at least immediately afterwards. But scientists aren’t really going to have anything particularly deep to say about this specific storm for months, if not years. During that time, data will be analyzed and compared, and other events will happen, and that’s really the stuff that we need in order to say much of anything other than, “We don’t know for certain.” In some ways, expecting anything else means forcing scientists to speculate and extrapolate in ways they aren’t usually comfortable with and that aren’t a terribly great way to understand the big picture.
Indeed, as The Washington Post’s Brad Plumer and Climate Central’s Michael Lemonick both explained, regardless of whether or not climate change leads to more frequent or intense hurricanes, global warming is causing sea-level rise that will exacerbate the storm surge from any cyclone that comes along—and it’s those kind of details that get lost in generalizations about extreme weather events.