How Climate Change Fuels Hurricane Patricia

23 10 2015

CSB52hJXAAEcXDL.jpg-largeBehind Patricia: How Climate Change Is Fueling the Strongest Storm Ever Recorded

Friday morning, Hurricane Patricia became the strongest storm ever recorded. It did so at a rate so rapid that it took scientists by surprise: Its winds grew from 60 MPH to a sustained 200 MPH in just over a day’s time. As it nears the southwestern coast of Mexico, the National Hurricane Center is calling Patricia “potentially catastrophic.” And it almost certainly wouldn’t be so powerful if human activity hadn’t warmed the waters to near-record temperatures before it developed.

“Patricia was fueled by ocean waters that were a near-record-warm 87 F, which would not have been so warm without climate change,” Jeff Masters, the director of meteorology at the Weather Underground, wrote me in an email. “It is fair to say climate change increased the odds of getting such a strong storm.”

This year has so far been the hottest on record for land and ocean surfaces alike; just this Wednesday, the National Oceanic and Atmospheric Administration released a report announcing that last month was the hottest September yet recorded. NOAA explained that the “oceans were also much warmer than average across vast expanses, with much of the eastern and equatorial Pacific Ocean, the Barents Sea in the Arctic, and large parts of the western North Atlantic and Indian Ocean record warm.”

One of those warm spots was the Northeast Pacific Basin, where Patricia was formed.

Kevin Trenberth, a senior climatologist at the National Center for Atmospheric Research, explained how the unusually hot ocean waters helped Patricia get its unusual power.

“The sea surface temperatures are so high over such huge areas,” he told me, “that the moisture flowing into the storm, that provides its primary fuel, must be higher than it has ever been before.”

“It still requires the right setup to convert that into an intense storm but the environment is surely ripe,” Trenbeth said. “That consists, of course, of a substantial El Niño-related component but also the background global warming that has a memory through the ocean heat content.” Some of the warmth fueling Patricia comes from a hotter-than-usual El Niño—the complex series of climatic shifts typically marked by the appearance of unusually warm waters in the equatorial Pacific—and some of it comes from us.

“It is the combination of El Niño plus global warming that breaks records, and of course this is far from the first,” Trenbeth said, “Haiyan in the Philippines in November 2013, Pam in Vanuatu in March 2015, and now Patricia: let alone all the other Typhoons that have devastated Japan, China, Taiwan, the Philippines, etc this year.”

Of course, we can’t say Patricia was entirely caused by climate change, but the conditions were so ripened by it that it’s hard to discount that it played a role.

In fact, in what’s either an uncanny coincidence or a profound display of prescience, Tom Knutson, a climate modeler with NOAA, just published a paper outlining how climate change may impact tropical cyclone activity around the globe.

“Probably just a big coincidence,” he tells me, “but Patricia is an an area we identified as having the largest future increase in [Category 4 and 5 hurricane] frequency.” Knutson had just pegged the NE Pacific basin as the region likeliest to see more hurricanes in coming years—and more powerful ones, too. He notes that he tries “not to make too much of these small-scale sub-regional details in our projections,” but that “we project for the NE Pacific basin as a whole about 8 percent increase in hurricane wind intensities by the late 21st century and almost a 500 percent increase in [Category 4 and 5] days.”

Knutson says that the anthropogenic signal—a distinct human influence—in hurricane activity is “likely already underway,” though it is hard to detect in historic storm patterns thus far.

But the trend is at least beginning to seem apparent. After all, this year has seen a record number of Category 4 and 5 hurricanes and typhoons.

“Yes also with regard to the record number of Category 4 storms, there is undoubtedly a human-induced global warming component,” Trenbeth said. “When natural variability (El Nino) and global warming go in the same directions we break records.”

Jeff Masters concurs. “I expect that we will see the strongest hurricane getting stronger as the oceans continue to warm, and there will be an increase in high-end Category 5 storms like Patricia and Super Typhoon Haiyan (2013) in the coming decades.”

Some meteorologists are already arguing that we’re going to need to add new categories to properly describe these new behemoth storms.

“The Saffir-Simpson hurricane wind scale rates hurricanes on a scale of 1-5, depending on the maximum sustained winds,” Hal Needham, a storm surge scientist at Louisiana State, wrote in WXShift. “The strongest hurricanes, categorized as Category 5 storms, produce maximum sustained winds exceeding 155 mph and inflict catastrophic wind damage… If the Saffir-Simpson Hurricane Wind scale were a continuous scale, with no upper bound, Patricia might be classified as a Category 7 hurricane.”

As the meteorologist and climate writer Eric Holthaus notes, “Patricia is now very close to the theoretical maximum strength for a tropical cyclone on planet Earth.” And of course, in the future, “Category 7” storms like Patricia will only become more frequent.

“It is an indicator of what the future looks like,” Trenbeth said. “The storms occur in different places but eventually are apt to come your way, if you live on the coast where hurricanes track.”

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