Most people understand that a hurricane is a vast, natural heat engine fueled by warm surface sea water. It follows then that, all other things being equal, warmer sea surface temps mean more intense tropical storms and hurricanes. But all things are decidedly not equal. windshear, loop currents, upswells, wave height and depth, and watery downdrafts all vary and complicate the already fiendishly intricate variables at play in storm meteorology and climate change. A new study on tropical cyclogenesis seeks to isolate the effect of greenhouse forcing from that bevy of variables and the results are no surprise to anyone:

ArsTechnica — The resulting data was compared to possible contributing factors, such as the El Niño Southern Oscillation, average global temperature, local temperature around the Earth, and sea surface temperature in the tropical Atlantic. Since hurricanes are fueled by warm surface water, the data correlated most strongly with global temperature and sea surface temperatures in the area where hurricanes form.

The researchers used these relationships to create statistical models of hurricane behavior. Based on the last 90 years, those models calculated that a 1°C warming of the globe increases the probability of a hurricane storm surge the size of Hurricane Katrina’s by two to seven times—a startling rise.

That’s larger than previous estimates, which relied on climate model simulations. If accurate, the study tells us that putting hurricanes on climate steroids will have costly consequences. But it also tells us that the warming of the 20th century is already affecting us in a significant way. The paper concludes that “we have probably crossed the threshold where Katrina magnitude hurricane surges are more likely caused by global warming than not.” In other words, storm surges of that size are now at least twice as common as they were a century ago.