Was 2011 a record year for severe weather events and natural disasters? And to what extent can this trend—if indeed such a trend exists—be tied to climate change? Before we try to answer those questions, we need to try to get a bead on what exactly is “severe weather” and how precisely we define a “disaster.” And it’s not as easy a task as you may think. An excellent blog post over at The Green Grok called “Global Warming and Severe Weather: Is There a Link?” by Bill Chameides, Dean of the Nicholas School for the Environment at Duke University. He begins by citing NOAA data that find that “the number of severe weather events in the United States costing a minimum of $1 billion increased from about 1.2 per year in the early 1980s to about 5 in the 2000s, and 2011 saw a record high of 14 such events.” However, what are we counting? And at what point does something that is merely bad become a “disaster”? Well: “analysts often turn to metrics that integrate across all events—for example, the total damage costs (or alternatively the total insured losses) that natural disasters impose on the insurance industry in a given year.” All well and good. But then there are socio-economic factors. Looking at damage costs from year to year may not be so straightforward. When the affluent move to coastal communities, those populations, and the amount of property that can be damaged by things like hurricanes and floods, increase. So just identifying whether there is a problem is...well, a problem, without even getting to the more basic issue of attributing phenomena to climate change. (And other types of natural disasters such as earthquakes are unrelated ti climate change.) “It seems like the recent past has delivered some strange weather. Is it part of a long-term trend? A trend due to global warming? If you require rigorous scientific evidence, the answer, at least today, is that we just don’t know.” Nonscientists (and probably many scientists) are uncomfortable with “fuzzy” conclusions. And that’s understandable. Ultimately, Dr. Chameides writes, it comes down to basic attitude: do we act prudently now assuming that there is a link between severe weather and climate change, or do we turn a blind eye and assume that there is no link? If the latter, are we prepared for the consequences of guessing wrong? There is more at the New York Times’ Dot Earth blog.