We are halfway through the hurricane season, Hurricane Harvey’s destruction stretches along the Texas coast, and Hurricane Irma has laid a trail of devastation from the Cape Verde Islands to Georgia. Hurricane Jose is swirling in the Atlantic, while a third Atlantic hurricane, Katia, struck Mexico’s eastern coast late on 8 September.
As global temperatures continue to rise, climate scientists have said this is what we should expect – more huge storms, with drastic impacts.
However, during these shocking events, many leading politicians and the media paid little attention to the reasons behind these disasters. The UK Foreign Office minister Alan Duncan went so far as to claim that Caroline Lucas (co-leader of the UK Green Party) was lacking “humanity” when raising climate change’s effect on the hurricanes during a recent Parliamentary discussion.
Following any shocking event, it is the task of governments and experts to dissect the reasons behind the events in order to stop them happening again. For example, when London suffered a series of terrorist attacks, the government, intelligence agencies and the police came together to answer the questions of: who it was, why did it happen and how can it be prevented from happening again?
Hurricane Harvey and Irma are indeed natural disasters, which have wreaked destruction and human misery, but their power is a symptom of climate change. To reject any discussion of this issue, as Mr Duncan did, is to reject the duty of protecting the “humanity” of future victims.
“The short version is, climate change makes these very bad storms worse,” said Sean Sublette, a meteorologist with Climate Central, a nonprofit group that studies climate change. “It’s not the approximate cause of the storm, but it makes these bad storms worse. And in the case of a really bad storm, climate change can make it totally disastrous or catastrophic.”
Unprecedented records being set
Irma was a full-fledged hurricane in less than 24 hours. It was so strong and so robust that it seemingly set a record for the number of records it set.
According to Phil Klotzbach, a noted atmospheric research scientist at Colorado State University:
- When Irma reached Category 5 — the strongest there is — it stayed there for more than three days, the longest run since forecasters began using satellites to monitor tropical storms more than a half-century ago.
- Irma blew 185-mph maximum sustained winds for 37 hours — the longest at that intensity anywhere on Earth since records started being kept.
- Irma generated the most accumulated energy of any tropical cyclone in the Atlantic tropics on record.
But if there’s one statistic that sums Irma up, it’s this one: it generated enough accumulated cyclone energy — the total wind energy generated over a storm’s lifetime — to meet the National Oceanic and Atmospheric Administration’s definition of an average full Atlantic hurricane season. By itself, it was more powerful than 18 of the 51 full hurricane seasons since 1966, according to Klotzbach’s calculations.
Climate Change’s role
If Hurricane Harvey had happened at the end of the 20th century, that amount of rain falling in Houston in a single storm would have been rare—a 1-in-2,000 year event, said Kerry Emanuel, an MIT professor of atmospheric sciences. But as temperatures continue to rise, those rare events are becoming increasingly less rare, he said.
There are myriad reasons why individual storms develop as they do, including a combination of natural and manmade causes. That can make it hard to assess what role climate may have played in an individual storm (though the science behind attribution studies is getting better all the time). What scientists who study hurricanes are confident in, though, is the underlying physics that show that warmer temperatures are among the factors changing the way that storms form.
This summer’s hurricane season has been a particularly warm one in the region of the Atlantic where hurricanes form, with sea surface temperatures between 0.5°C (0.9°F) and 1°C (1.8°F) above average, according to data from the National Oceanic and Atmospheric Administration (NOAA).
Those high temperatures mean hurricanes will store more water, which they can eventually dump when they make landfall. Climate scientists blame high temperatures during Hurricane Harvey’s formation and along its path for the more than 50 inches of rain dropped on Houston.
“You fit all the data together and ask what is the likelihood for 100 millimeters, 200 millimeters of precipitation,” said study co-author Sarah Kapnick, a researcher at the NOAA, before the Harvey hit Texas. “As you get to higher and higher values of precipitation it becomes less and less likely without climate change.”
“A warmer ocean makes a warmer atmosphere, a warmer atmosphere can hold more moisture,” says Gabriel Vecchi, a professor of geosciences at Princeton University who studies extreme weather events. “So, all other things equal, the same storm in a warmer planet would give you more rainfall.”
We saw this in greater Houston from Harvey and along the 240-mile stretch of the Atlantic coast from Jacksonville, Florida, to Charleston, South Carolina as a result of Irma’s storm surge and heavy rains.
According to the 2014 National Climate Assessment, the intensity, frequency and duration of North Atlantic hurricanes have increased since the early 1980s. The frequency of the strongest storms—category 4 and 5 hurricanes—has increased too.
Now, scientists just need to convince the policymakers charged with helping prepare communities for hurricanes that the dangers are only increasing.
What About the ‘Hurricane Drought’ Claim?
On 25 August, as Hurricane Harvey gained strength and headed for the Texas coast, the conservative Heartland Institute put out a press release decrying any efforts that scientists and the media might make to explain the climate influences on the storm. Bette Grande, a research fellow with Heartland, said: “Though it has been nearly 12 years since a major hurricane has hit the United States—Harvey will be creatively spun to ‘prove’ there are dire effects linked to man-created climate change.”
She was referring to the concept of a so-called “hurricane drought” that climate deniers have been circulating—which they say debunks the work of climate scientists.
While no “major hurricanes” made landfall in the United States between 2005 and this year, those weren’t weak tropical storm years—the biggest storms just didn’t hit the U.S. In 2013, Typhoon Haiyan devastated the Philippines with the highest wind speeds ever seen—until Hurricane Patricia broke that record two years later off Mexico’s Pacific Coast, and several other cyclones wreaked havoc elsewhere around the world in the intervening years.
In a 2015 study published in the journal Geophysical Research Letters, two NASA scientists concluded that the lack of major storms in the United States during that period was merely “a matter of luck.”
People in some parts of the United States might also disagree with the concept of a “hurricane drought” during that period.
“Tell the people of coastal Texas that Ike was not a major hurricane,” said Emanuel, the MIT scientist. “Well, Ike was technically just under the ranking of major hurricane, and it completely destroyed a huge part of coastal Texas. Now, tell the people of New York that Sandy wasn’t a major hurricane.”
“There were plenty of hurricanes in that stretch of 12 years,” he said. “They just didn’t happen to make landfall as strong storms in the United States.”