Kossin and his colleagues at NCDC created a 28-year record of storm images across the world’s seven hurricane basins, from 1982 to 2009. Then they used a computer algorithm to compute each storm’s maximum strength, removing human error and unpredictability from the equation. The result? The scientists found that globally, hurricane wind speeds are increasing at a rate of a little more than two miles per hour per decade, or just faster than six miles per hour over the entire period.
There are some key caveats, though, the biggest being that the trend they found was not statistically significant at usually accepted levels. (For nerds: the p value was 0.1). But there were strong and significant trends in some hurricane basins of the world, especially the North Atlantic (the region encompassing the Caribbean, Gulf of Mexico, and open Atlantic north of the equator), where storms have been strengthening at the rate of nearly nine miles per hour per decade (see chart above). But other basins offset that, including the western North Pacific, which showed a negative trend.
The punch line, then, could hardly be called overwhelming. But as Kossin explains, that may be precisely what you expect to see once you’re finally analyzing the troublesome hurricane data reliably. These results, after all, are quite consistent with the idea that the signal of hurricane intensification might be just now emerging from the “noise” of natural climate variability. “What we’re observing could very easily fit into an assumption of this greenhouse gas forced trend in the tropics and the effect that it has on tropical cyclone intensity,” says Kossin.