Clarifying the Links Between Climate Change and Fiercer Hurricanes

As Atlantic hurricanes intensify, it's clear that failing to act on science will increase the risks from future storms.
By Bob Berwyn ,
A satellite image shows Hurricane Irma passing the eastern end of Cuba on the morning of September 8th, 2017.

As Hurricane Irma cuts a deadly path through the Caribbean en route toward Florida, climate scientists have issued a stark warning: Expect more of the same in the global warming era.

Climatologists have shown the connection between powerful hurricanes and climate change—a fact that the media and Trump administration officials sometimes obscure—as researchers from Woods Hole Research Center, a leading climate think tank, said in a statement posted September 6th.

Last April, the New York Times was lambasted by climate scientists for publishing an opinion column by Bret Stephens downplaying links between extreme weather and climate, and, in recent days, top government officials refused to answer questions about links between global warming and Hurricane Harvey.

"Climate change is increasing the number of very intense hurricanes, and tends to make all hurricanes more damaging," said Philip B. Duffy, president of the WHRC.

As of Thursday, Hurricane Irma fits this pattern, having killed at least 10 people as it swept across small island states in the eastern Caribbean Sea. Barbuda took the first direct hit from the storm's 185 mph winds, the strongest ever recorded in a hurricane in the open Atlantic Ocean. Officials reported Thursday that up to 90 percent of the houses on the island were destroyed, and videos posted on social media showed forests completely stripped of leaves and branches.

Similar damage is being reported from the Dutch Antilles and parts of the Virgin Islands. As if that weren't enough, newly formed Hurricane Jose is projected to graze the same area with winds of more than 100 mph. Another tropical system, Hurricane Katia, developed in the western Gulf of Mexico, triggering hurricane warnings along the coast of Mexico.

National Hurricane Center forecaster Eric Blake said it's the first time in the modern era of satellite observations that three major hurricanes have threatened to make landfall at the same time in the Atlantic. "Unparalleled here and totally ridiculous given #Irma," he posted on Twitter.

A Warming Ocean Means Fiercer Hurricanes

Before reaching Florida, Irma will pass over some of the warmest ocean water anywhere on the planet right now. As a result, it's not likely to weaken before reaching southern Florida this weekend. If, as forecast, it makes landfall as a Category 4 or 5 storm near Miami, it will likely become the costliest disaster in United States history in terms of property damage.

Along with winds that will tear some houses apart, the storm could push as much as 10 feet of seawater inland across the state's low-lying coastline, potentially flooding as much terrain as Harvey did in Texas. Already, tens of thousands of people are subject to evacuation orders in Florida and Georgia, and the storm may also threaten the Carolinas, according to the latest forecasts from the NHC.

Duffy said that extreme hurricanes like Harvey and Irma "naturally" raise questions about the links to human-caused climate change. And the science shows with little doubt that extreme precipitation and the likelihood of very intense storms increases in a warmer climate.

"What this adds up to is that climate change is increasing the number of very intense hurricanes, and tends to make all hurricanes more damaging when they do occur," he said.

It's important to remember that more than 90 percent of the heat trapped by greenhouse gases ends up being stored in the ocean, says Kevin Trenberth, a climate scientist at the National Center for Atmospheric Research. Before greenhouse gas pollution started building up, hurricanes cooled the ocean surface when they passed. Now, the heat that's accumulated deep in the ocean replenishes surface waters churned up by hurricanes.

"That is where the global warming plays a role in continuing to fuel the warm waters and the evaporation of moisture into the atmosphere that leads to the huge precipitation and flooding risk," he says. And scientists aren't just guessing: In several recent extreme storms, instruments have measured all-time record high levels of water vapor in the atmosphere, as gauges on the ground have measured record rainfall.

Trenberth said human-caused global warming can increase rainfall between 5 and 15 percent on a linear scale, but that it can also magnify the intensity in other ways, fueling more intense, bigger, and longer extreme events.

Preparing for Elevated Risk

It's challenging to find a global warming signal in the noise of natural hurricane variability, which is influenced by El Niño cycles and the strength of the African monsoon, among other things. But researchers started solving that puzzle nearly 10 years ago by focusing on the peak intensities of storms.

When they did that, they found Atlantic tropical cyclones have strengthened on average, "with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere," according to a 2008 study published in the journal Nature.

A street is flooded during the passing of Hurricane Irma on September 6th, 2017, in Fajardo, Puerto Rico.

They also found a significant upward jump in peak wind speeds as well as the duration of strong winds, trends reflected by the development of Irma, which generated stronger and more sustained winds than any other Atlantic hurricane on record.

The climate researchers at Woods Hole say the science is telling us that communities need to prepare for elevated risk from extreme weather events, including hurricanes.

"Failure to do this subjects us to more potential harm than is necessary," said Duffy, explaining that the current administration's recent move to undo federal flood risk management standards is a step in the wrong direction, because it will expose more infrastructure to flooding.

He also said fiscal support for scientific observation and modeling programs is critical, including those needed to understand and predict extreme weather events and how they are affected by climate change, in order to save lives and property.

"Finally, of course, this tragedy reminds us (once again) that we need to take immediate and effective action to prevent future climate change by reducing emissions of greenhouse gases to the atmosphere," he said.

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