It is officially the strongest hurricane ever measured by the U.S. National Hurricane Center, based on both its wind speed (175 knots) and its minimum central pressure (880 millibars). The wind measurement “makes Patricia the strongest hurricane on record in the National Hurricane Center’s area of responsibility (AOR) which includes the Atlantic and the eastern North Pacific basins,” the center said this morning.
And in this case the measurement has added weight because it is based on data collected from an aircraft, rather than mere satellite imagery. “We would like to acknowledge deeply the Air Force Hurricane Hunters for their observations establishing Patricia as a record-breaking hurricane. Clearly, without their data, we would never have known just how strong a tropical cyclone it was,” wrote National Hurricane Center forecaster Richard Pasch this morning.
So how could this happen? The first reason is the presence of an El Niño year, which generally leads to hyperactive hurricane activity in the Eastern Pacific basin, says Kerry Emanuel, an MIT hurricane expert, by e-mail. Emanuel has derived a way of measuring the maximum potential intensity that a hurricane can achieve, in light of the climatic conditions in which it forms, which include the sea temperature as well as the temperature high in the atmosphere above the storm.
“Potential intensity was particularly high in the region where Patricia developed,” Emanuel says. He provided this figure to underscore the point:
So what does this say about climate change?
Certainly, record-breaking hurricanes raise questions about longstanding predictions that global warming, by raising ocean temperatures, should also strengthen these storms. The issue, however, is beset by data-related difficulties, since storm measurement techniques are continually improving (creating a kind of apples-and-oranges problem when comparing past strong storms with present ones) and are also highly variable around the world — thus, hurricane hunter flights are far more common in the Atlantic than in the Northeast Pacific, where Patricia formed.
Still, there have been widespread predictions that hurricanes should become stronger, on average, in a warmer world. Summarizing the current research, the Geophysical Fluid Dynamics Laboratory of the National Oceanic and Atmospheric Administration puts it this way: “Anthropogenic warming by the end of the 21st century will likely cause tropical cyclones globally to be more intense on average…. This change would imply an even larger percentage increase in the destructive potential per storm, assuming no reduction in storm size.”
But of course, it’s not the end of the 21st century — it’s 2015. So are we seeing the change already, with Haiyan and now Patricia?
“The fact that we have broken records now in the eastern and western Pacific is curious, but we are still dealing with the statistics of small numbers so inferences are dangerous,” Emanuel says by e-mail. Emanuel also cautions that because most Eastern Pacific storms are not measured by aircraft, there could have been a stronger one in the past that was not detected. Nonetheless, he recently published research suggesting the theoretical possibility of hyper-strong hurricanes in certain regions as global warming continues.
While one storm is only one storm and can never substitute for a comprehensive statistical analysis, the fact remains that the link between warm seas and strong storms — the theoretical reason for believing hurricanes will worsen due to climate change — is starkly apparent in this case.
“The [sea surface temperatures] are so high over such huge areas, that the moisture flowing into the storm, that provides it primary fuel, must be higher than it has ever been before,” says Kevin Trenberth, a climate researcher at the National Center for Atmospheric Research, by e-mail. “It still requires the right setup to convert that into an intense storm, but the environment is surely ripe. 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.”
Trenberth points out that ocean surface temperatures in the region are “the warmest anywhere around” — more than than 30 degrees Celsius, or 86 degrees Fahrenheit. “The subsurface ocean is exceptionally warm as well,” he adds.
“As ocean temperatures continue to warm as a result of human-caused climate change, we expect hurricanes to intensify, and we expect to cross new thresholds. Hurricane Patricia and her unprecedented 200 mile-per-hour sustained winds appears to be one of them now, unfortunately,” adds Michael Mann, a climate researcher at Penn State University.
The global prediction of more intense hurricanes is one thing, but what about a regional prediction? After all, hurricanes (and typhoons) form in different regions or “basins” of the world, and these might be differentially affected in a world that is warming.
A recent study in the Journal of Climate by NOAA’s Thomas Knutson and colleagues actually did find that the northeast Pacific, where Patricia formed, is an area where storms are expected to intensify. “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 Cat 4-5 days,” says Knutson by e-mail.
The key — and difficult — question is whether this change is already manifesting itself. Theoretically it should be, but it’s also not clear in the data, says Knutson:
I would speculate that this signal, if it were to happen in the real world, is likely already underway at least to some extent based on the anthropogenic warming we’ve already had to date. But, importantly, there does not seem to be a detectable signal of this type in the real world to date, at least based on storm lifetime maximum intensity data since 1982.
So in sum, scientists will never attribute one single event to climate change or say that it was caused by a warming planet; and with this event as with all weather events there are multiple causes, most prominently El Niño.
Nonetheless, we can say this: Record-setting hurricanes like Patricia are consistent with one major prediction that climate researchers have made for some time about the consequences of a warming world.
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