Ever since I heard the link I was hoping for something more solid than the weak associations I was hearing about on NPR and other news sources. It seemed very preliminary, and a bit worrisome that, especially in the foreign press, that they were claiming things like the New Orleans/Katrina disaster was the first example of a global warming disaster. The evidence simply wasn’t conclusive and in general in science, results need to age. It’s like cheese or wine, you wait for the results that get better with time, and you have to be patient.
I’m reading now in New Scientist that the hurricane link, when evaluated through proxy-data over about 3 centuries, is pretty weak. (Nature article here)
To answer that question, scientists like to look at hurricane activity in the past, which can tell them whether or not recent activity is an abnormal spike in the record. But reliable observations of hurricane activity over the Atlantic only go back to 1944, so scientists have to turn to other indicators.
One team of scientists examined Caribbean corals and the abundances of a particular plankton to see how hurricane activity, which affects both groups, changed over the past 270 years.
…
The researchers compiled data of these coral proxies, or stand-ins, for direct hurricane data, and reconstructed wind shear and sea surface temperature records for the past 270 years, giving them an idea of what hurricane activity might have been like.
They found that the downward trend in the number of hurricanes from the 1940s to the 1970s was replicated by the reconstruction and is attributable to greater wind shear, which likely stifled hurricane development.
The scientists also used the reconstruction to compare the current upswing in hurricanes to past active phases and found that it was “unexceptional.”
I’m not an expert in this field whatsoever, so I have to rely on others’ analysis to see what this means in the context of other results in the field. But this statement in particular seems strange to me:
So though sea surface temperatures have been rising with global warming over the past century, the authors of the new study, detailed in the June 7 issue of the journal Nature, say that higher wind shear won out over any fuel hurricanes would have received from the water during the lull from the 40s to the 70s.
But in the future, if wind shear decreases (which could happen if there were fewer El Niño events), and sea surface temperatures continue to rise, storms could have longer lifetimes, form more often or become more intense, the authors concluded in their paper.
Other studies, including another recent Nature study that examined sediment cores from a Puerto Rican lake, have put together these past hurricane records from proxy data and concluded that wind shear may be more important than the ocean’s temperature in influencing hurricane activity.
From what I recall of the 40s to 70s, that was a period of relative cooling. It makes physical sense that increased temperatures in bodies of water will lead to more intense storms, as warmer waters are absolutely responsible for hurricane activity. However, it’s clear that at the very least, temperature is dampened by other factors. I hope Real Climate pitches in and gives a good overview of where the field is in terms of this understanding.
I am worried however, that in classic denialist fashion, the anti-GW cranks will latch onto this and say, “See! You’re wrong! You don’t know anything!” when it was clear to me that this connection has always been somewhat tentative (and still not completely ruled out). The science of global warming is clearly not dependent on this result, but some people who were raising alarms with the suggestion of a link will likely be used to further disparage the science.
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