Climate change is intensifying even 'weak' hurricanes

Global warming has long been known to affect many of the characteristics of hurricanes. The science clarifies that, although it is difficult to answer the question of whether climate change is making hurricanes more frequent, there are changes that are related to the increase in temperature, such as intensity.

A new study published in the journal Nature analyzed data collected by thousands of scientific instruments that measure ocean currents around the world. Their analysis found that not only hurricanes are transformed by global warming, but also less intense tropical cyclones. Hurricanes are tropical cyclones that have winds of more than 120 kilometres per hour.

As per the study less intense tropical cyclones, such as Category 1 tropical storms or hurricanes, are likely to intensify at a rate of about 1.8 meters per second every decade as a result of global warming.

Guihua Wang and colleagues use a unique set of ocean current observations—high-quality current measurements made by floating devices called surface drifters—to quantify tropical cyclone intensity in a new way that complements traditional methods.

There is a close relationship between tropical cyclones and ocean currents, and drift devices deployed by the National Oceanic and Atmospheric Administration provide highly accurate current measurements. The authors' analysis shows that weak tropical cyclones, classified as Category 1 tropical storms and tropical cyclones, have been intensifying from 1991 to 2020 as a result of global warming.

So how strong are the cyclones getting?

Ocean measurements suggest that tropical cyclones are likely to intensify at a rate of about 1.8 meters per second every decade. This study suggests that this trend occurs in storms around the world. However, this conclusion, for now, only applies to weak tropical cyclones, such as Category 1 tropical storms and hurricanes.

That's because not enough data has been collected for stronger storms, which means there isn't enough evidence to say yet. Unlike other studies that have been published on the subject, this one did not use data from satellites, but from devices that measure the speed of ocean currents at certain points. By measuring these currents, scientists can estimate the wind speed of a tropical cyclone.

But in a commentary on the new research, also published in Nature, atmospheric scientist Robert Korty said he suspects the findings are likely to hold true for stronger cyclones as well. He pointed out that the measurements included in this study are instantaneous in time. So some of those cyclones may have been weak when they passed the sensors in the ocean, but then intensified to become stronger cyclones.

Intense rainfall

In an analysis by NASA researcher Angela Colbert, she concludes that while large-scale changes in hurricanes are difficult to forecast, global climate models predict that climate change will make hurricanes likely to cause more intense rainfall and are at increased risk of coastal flooding. “In addition, the global frequency of storms may decrease or remain unchanged, but the hurricanes that do form are more likely to become intense,” Colbert summarizes.

Scientist Tom Knutson noted in this analysis that even if hurricanes themselves do not change due to climate change, "storm surge flooding will worsen with rising sea levels." The expert indicated that models show increases in the rate of rainfall from a hurricane by the year 2100 and this means that hurricanes are likely to cause heavier rainfall when they make landfall.

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