The press has been quick to jump on the idea that post-tropical cyclone Sandy (it was not a hurricane at landfall) was worsened by anthropogenic global warming and that “superstorms” are here to stay.
But I must ask the impertinent question: could anthropogenic global warming actually have lessened the impacts of Sandy?
There are basically three pro-global warming talking points involving Sandy: 1) global warming has caused sea levels to rise, thus making the storm surge larger, 2) global warming has led to higher sea surface temperatures and thus stronger hurricanes, and 3) global warming is making extratropical circulation features more conducive to intense and slower moving storm systems.
There is precious little evidence to definitively support any of these points when applied to Sandy, and, in fact, there exists a body of evidence pointing to the opposite conclusion—that anthropogenic global warming may have actually acted to mitigate the intensity of Sandy. Perhaps what lies closest to our current best understanding is that anthropogenic global warming made little contribution one way or the other.
Let’s start with sea level rise. Water levels at New York City’s Battery Park location have been measured and recorded since 1856. The full record shows an overall (relatively steady) rise of about 0.11 inches per year, for a total rise between 1856 and now ofjust a bit more than 17 inches. How much of this has to do with anthropogenic global warming? Maybe a third, or about 6 inches. Of the rest, about half was caused by a subsidence of the land (geological processes related to the end of the last ice age, see Engelhart et al., 2009 for example), and the remainder to a warming up from the naturally occurring cold period which ended in the mid-19th century. So of the total 17.34 feet of water(above the station datum) recorded at The Battery tide gauge during the height of Sandy, about 0.5 feet of that could probably be linked to anthropogenic global warming. This is not nothing, but the overwhelming majority of the damage done by the storm surge would have happened anyway. For comparison, the influence of the full moon that night was about as large as the influence of anthropogenic global warming.
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