Warming makes hurricanes stronger, other effects unclear

Union of Concerned Scientists News Center: Every hurricane season, the Union of Concerned Scientists (UCS) receives questions about the science linking hurricanes to climate change. In short, global warming is making the ocean warmer, which in turn makes it more likely for hurricanes, when they do form, to become stronger and more destructive. Meanwhile, the link between global warming and the number of hurricanes that form each year remains unclear.

When examining the link between climate change and extreme weather, it is important to bear in mind that each storm is just one data point in Earth’s climate history. Statistically, an individual hurricane is like a single at-bat for a baseball player, while conclusions about how climate change affects hurricanes is like calculating a baseball player’s batting average. Scientists draw meaningful conclusions from analyzing many storms over many decades.

Besides contributing to hurricane intensity, climate change is also causing sea levels to rise. As the ocean warms and expands and as land-based glaciers melt into the ocean, sea level rises and storms reach further inland before dissipating. Higher sea levels give coastal storms a higher starting point when they make landfall, especially if storms make landfall during high tides. Unless communities improve coastal planning, hurricanes will cause more property damage over time due to the proliferation of public and private development along coastal areas.

Two links between climate change and hurricanes are less clear, however. Scientists aren’t sure how climate change will impact wind shear—the difference in wind speed and direction in a given location.

…Often, people don’t understand that scientists have varying levels of certainty when it comes to different consequences of climate change. Climate contrarians try to take advantage of this knowledge gap when they conflate scientists’ relatively low certainty about how climate change affects hurricanes with their relatively high certainty regarding other, serious consequences of climate change, including sea level rise, long-term drought, reduced crop yields and species extinctions.

Much of the scientific uncertainty regarding climate change and hurricanes has to do with a lack of data. The most accurate hurricane data come from satellites, which have been observing weather for a little more than 30 years. And while pre-satellite data from ships and land-based stations can help scientists understand when hurricanes hit and roughly how powerful they were, those data are not specific enough to allow scientists to draw precise conclusions. Scientists have a less precise, but longer record of hurricane data from the geologic record….

Before the year 2004, only two tropical cyclones had ever been noted in the South Atlantic Basin, and no hurricane. However, a circulation center well off the coast of southern Brazil developed tropical cyclone characteristics and continued to intensify as it moved westward. The system developed an eye and apparently reached hurricane strength on Friday, March 26, before eventually making landfall late on Saturday, March 27, 2004.
The crew of the International Space Station was notified of the cyclone and acquired excellent photographs of the storm just as it made landfall on the southern Brazilian state of Santa Catarina (the storm has been unofficially dubbed “Cyclone Catarina”).