Both papers are published this week in the Proceedings of the National Academies of Science. The first comes from a team at NOAA and the University of Wisconsin—Madison. Looking back over decades of storm data, they found increasing strength among tropical cyclones, and increasing probability of major storms. In particular, there is a “positive trend” toward storms that reach levels 3 to 5 on the Saffir-Simpson hurricane scale. Though … it’s really hard to call this trend positive. These are, after all, the storms that are most likely to bring death and destruction to coastal areas, like those that recently devastated Puerto Rico.
The NOAA paper isn’t really making predictions about where storms are going in the near term. It’s just reviewing the information back to the 1970s to confirm what might have already seemed obvious — storms are getting worse. It’s just that now they’re getting worse … with a 95% probability level. Both the possibility of a storm developing, and the possibility that a storm will reach higher intensities has increased.
The second paper, this time from a NOAA team paired with the University Corporation for Atmospheric Research in Boulder, Colorado, doesn’t look so much at the intensity of storms, but where those storms are occurring. The authors of this paper show that, even more than the growing intensity, the changes over the last forty years are visible in the tracks that tropical storms have taken and in the places where they form. For example, people living around the southern Indian Ocean could be forgiven for thinking that tropical storms are on the decline—because they absolutely have declined in that area. On the other hand, Americans looking at storms in the Atlantic are definitely right in thinking that storm frequency has increased. Overall, storms are up around the world, but they’re not up evenly. Not everything in the pattern of storm development can be mapped directly to warming oceans, but human-caused warming appears to be the driving factor.
One thing that the location team did that the intensity team did not was to take the model into the future, and that’s where an unusual effect appears. As the oceans continue to warm throughout the remainder of the 21st century, the warming oceans continue to push the development of storms away from the equator. And by the final decades of the century, the number of tropical cyclones begins to decrease … because these storms have been pushed right out of the tropics. There may be storms, they just won’t be tropical storms.
Which probably won’t be a lot of comfort to anyone in their path.