A Candid Conversation with Climate Scientist Kevin Trenberth on how Climate Change Alters Hurricanes, and Disinformation Distorts Science

Once castigated to get him fired, few today deny Trenberth's research finding stronger hurricanes from climate heating.

7 minute read 

For almost five decades, Kevin Trenberth has continued to add to our knowledge of climate change and how human activity is warming and altering the Earth. Global heating has changed rainfall characteristics to fuel stronger storms, causing incredible floods in some regions. But in other areas, longer, more intense droughts stress famers, causing famine and refugee crises. Meanwhile, sea level rise and more powerful hurricanes threaten coastal cities with storm surges and drowning downpours.

Some of Trenberth’s most well-known research involves climate change’s impact on hurricanes. Back in 2005, Trenberth published his first study of climate change and hurricanes, kicking up incredible criticism from industry and climate change deniers. Frightened in part by Trenberth’s research, Exxon Mobil released a commercial disguised as a news program, and sent it to local TV news stations in Gulf Coast cities to argue that climate change did not make Hurricane Katrina stronger when it destroyed New Orleans.

Now retired, Kevin Trenberth is a Distinguished Scholar at the National Center of Atmospheric Research (NCAR) in Boulder and an Honorary Academic in the Department of Physics, Auckland University in Auckland, New Zealand. 

We caught up with him at his house in north Auckland, near the coast overlooking the Hauraki Gulf. After 42 years working as a scientist in the United States, Trenberth has finally returned home to New Zealand. 

“What mustn’t happen is that you just tell the public that hurricanes are going to be more intense,” Trenberth tells The DisInformation Chronicle. “Some of them will be, but some will be bigger; and some will be longer lasting than they would have been 20 years ago. Even now, if you ask 100 scientists, I don’t think you get the right answer from more than about five.” 

This interview has been condensed and edited.

DICHRON: Back in 2005, you published an article in Science Magazine that examined what we knew about hurricanes at that time. Here’s what you wrote:

Trends in human-influenced environmental changes are now evident in hurricane regions. These changes are expected to affect hurricane intensity and rainfall, but the effect on hurricane numbers remains unclear. The key scientific question is not whether there is a trend in hurricane numbers and tracks, but rather how hurricanes are changing.

You concluded that humans were changing the climate and this was making hurricanes more intense. I remember thinking that this was a pretty bold thing to say at the time. 

TRENBERTH: This all dates back earlier, to about 1998, when I decided that changes in rainfall were probably going to be one of the most impactful things from climate change. But nobody had done anything useful, and people were only talking about how climate change would alter annual rainfall amounts in a given area.

I wrote a paper in 1998 that said we have to recognize that the most important thing was not how much rain fell annually, but things like intensity and the duration of individual rain events—How long and how hard was each rainfall.

DICHRON: Around that time, in the early 2000s, I was commissioned to write a feature looking at how changes in rainfall would affect farmers. Research was finding that annual precipitation might not change, but the rains would be more intense. So farmers had to plan for different types of tilling to prevent erosion of top soil. I didn’t realize this was your research.

TRENBERTH: Yes, you might get bigger downbursts. I had done quite a lot of work on rainfall but nothing on hurricanes. But in 2004, four hurricanes hit Florida, and a colleague at Harvard Medical School and I were convinced that the position NOAA had taken was wrong and misleading, saying that there was no influence of climate change.

He called a press conference about this that got some attention.

At the time of this press conference, I was a lead author on the section of the IPCC (Intergovernmental Panel on Climate Change) report that was dealing with changes in hurricanes. I had asked Chris Landsea, who was at the National Hurricane Center, to contribute to this.

But when I had this news conference in 2004, he kicked up a huge fuss, and resigned from the IPCC. He said that I had never done anything on hurricanes. That resulted in me writing that 2005 perspective in Science Magazine. 

DICHRON: After your piece in Science, Kerry Emanuel had an analysis that next month in Nature that found hurricanes were becoming more intense and destructive. 

TRENBERTH: Emanuel had a major article in Nature, and then Peter Webster and Judy Curry put together some quick work and published it in Science saying that indeed there is a trend with hurricanes and climate change. But they hadn’t processed the data properly, as it turns out in the end. And Peter Webster and Judy Curry have remained skeptics of aspects of climate change to this day. 

DICHRON: This same period in 2005 was also when I was reporting about Congressman Barton investigating climate scientist Michael Mann. Climate change was such a huge issue political issue at that time.

And it came to a head in late August, when Hurricane Katrina slammed into the coast of Louisiana and drowned New Orleans. Suddenly, everyone is talking about climate change and hurricanes, but denying the science that was being published. 

If you turned on CNN, the discussion about Katrina had talking heads denying any link between climate change and the images flashing on the screen of New Orleans underwater.

TRENBERTH: Certainly, that was true with NOAA (National Oceanic and Atmospheric Administration) and the National Hurricane Center. All the hurricane scientists were meteorologists. I don’t think they had ever thought about the hurricanes from the standpoint of climate science. 

DICHRON: Here’s one flimsy piece of reporting I found denying how climate change was affecting hurricanes. It actually appears in the news section of Nature.

Is climate change to blame?

It is impossible to say for certain. 

There is evidence that hurricanes are becoming more intense, but this may be due to natural variation. New Orleans was last hit by a hurricane in 1969, marking the end of a particularly violent couple of decades. This was followed by a relatively quiet patch in Atlantic hurricanes, lasting until 1995. Since then, storms have been heating up again.

I read that piece at the time and knew it was just wrong.

TRENBERTH: Right.

DICHRON: For weeks after, everyone was still talking about Hurricane Katrina, when on September 20 Senator Inhofe put out a press statement titled “Hurricane Blame Game.” It’s Inhofe just ranting about how everyone’s making up stuff about the link between hurricanes and climate change. 

Then along comes Roger Pielke Jr. at the University of Colorado and Chris Landsea writing a perspective that ignores the science with this take-home message:

While future research or experience may yet over-turn these conclusions, the state of the peer-reviewed knowledge today is such that there are good reasons to expect that any conclusive connection between global warming and hurricanes or their impacts will not be made in the near term.

Yet, claims of such connections persist.

Pielke Jr and Landsea spent a lot of energy back then churning up nonsense that denied how climate change was affecting hurricanes. Looking back, it’s hard to understand why people in the media gave them so much attention. Meanwhile, the fossil fuel industry was funding climate denialists who were attacking you and trying to get you fired.

TRENBERTH: That’s correct. I was in a very awkward position and couldn’t rebut this stuff myself. I was, however, a coauthor on an article in the Bulletin American Meteorological Society that rebutted the Landsea and Pielke Jr. stuff. 

DICHRON: All of this led me back in 2005 to look into what was happening at NOAA and later writing a story which then started a congressional investigation a year later. I kept seeing Chris Landsea all over the media. He was everywhere denying the link between hurricanes and climate change.

A month after Katrina hit, Landsea threw cold water on research by you and Emanuel and told CNN that the impact of global warming on hurricanes is “minimal for the forseeable future.” But Landsea hadn’t published anything in a science journal. Meanwhile, this other NOAA scientist had published a study finding that climate change was affecting hurricanes, but he never appeared in the newspapers. I confirmed this by looking through news databases.

So I called someone in the NOAA press office at their house, late at night. I didn’t want to call them at the office. I said, “Look, I’m seeing something that’s weird, that doesn’t make any sense. You’ve got a guy who’s published in a peer reviewed journal about hurricanes and climate change, but he’s never being quoted in the media. Chris Landsea is everywhere, and he hasn’t published anything. What is going on?” 

Silence on the other end of the phone.

I said, “I’m not trying to quote you or anything. I’m just trying to understand, because I’m going to send a freedom of information act request to figure out what’s happening.” 

And the person at NOAA helped me to write that FOIA. I got the emails back months later and wrote a story for Salon about how the White House was doctoring NOAA press releases, and political appointees were picking Chris Landsea to speak in front of the media denying any link between hurricanes and climate change.

What were you scientists seeing at the time?

TRENBERTH: I had a very good friend who was at one part of NOAA. But on the operational side—the Weather Service side—there was complete denial of any aspects of climate change. 

DICHRON: Days after Hurricane Katrina hits a journalist named Ross Gelbspan, who wrote a couple of really important books early on about climate change, wrote an essay in the New York Times that said Hurricane Katrina’s real name is “climate change”

Against this background, the ignorance of the American public about global warming stands out as an indictment of the U.S. news media.

When the American press has bothered to cover global warming, it has focused almost exclusively on its political and diplomatic aspects and not on what the warming is doing to agriculture, water supplies, plant and animal life, public health and weather.

For years, the fossil fuel industry has lobbied the news media to accord the same weight to a handful of global warming skeptics that it accords the findings of the Intergovernmental Panel on Climate Change - more than 2,000 scientists from 100 countries reporting to the United Nations.

Today, with the science having become even more robust - and the impacts as visible as the megastorm that covered much of the Gulf of Mexico - the press bears a share of the guilt for our self-induced destruction with the oil and coal industries.

Ross was always rather prescient and just kind of captured what was going on, didn’t he?

TRENBERTH: Sure, pretty much. But he could be hyperbolic. 

DICHRON: So as Katrina hit, scientists were making some tentative steps into explaining how climate change was affecting hurricanes, while many in the media were running in the opposite direction. But about a year later you reexamined some of the information from Katrina and found that some of the storm surge and destruction of New Orleans could have been caused by global warming. Is that correct?

 TRENBERTH: We had two papers where we did a whole bunch of simulations of Katrina and also Ivan, which was in 2004. Indeed, you boost the sea temperatures in these simulations and the hurricane got a whole lot more intense. 

This led me to make more confident statements. 

DICHRON: Back when I spoke to you in 2005, climate denialists were trashing the science, but the facts were that the oceans were warming, and these warm temperatures serve as energy for hurricanes. But the open question was whether this increased energy meant bigger hurricanes, or did it mean that we would have more frequent hurricanes.

TRENBERTH: One of the papers that I wrote was to understand the role of hurricanes in the climate system. The conclusion was that climate change would cause more activity of some sort, and the most efficient form is with hurricanes

Hurricanes have very strong winds that increase the amount of heat coming out of the ocean and into the atmosphere. I was looking at hurricanes in terms of the intensity, duration, lifetime of the storms, and the number of storms.

Most hurricane scientists only talked about number and intensity, because it’s very hard to get good statistics on hurricane intensity and size. 

DICHRON: And even today, 15 years later, it’s hard to see if climate change is increasing the number of hurricanes?

TRENBERTH: Yes, that’s still the case. In general, there are bigger storms, and longer lasting storms, and heavier rainfalls. 

These storms mix up the ocean and they take heat out of it. As a result, hurricanes leave behind them a cold wake. That prejudices the region against the next hurricane. It’s also one of the reasons hurricanes don’t follow on the same track. 

And you don’t just want to only focus on intensity, because there’s a natural cycle to the intensity of the storm. It can give up that intensity and become bigger—more energy in the storm—but it’s distributed a little bit differently. And then the storm can spin up again. 

DICHRON: So we’re adding more energy into the climate change system which is changing the physics of hurricanes. 

But the average person wants to know, “What the hell does this mean for me, living in New York, Louisiana, the Gulf of Mexico?”  The take-home message is that climate change is making it a lot worse to live in those areas because of hurricanes. 

TRENBERTH: In part, yes. What mustn’t happen is that you just tell the public that hurricanes are going to be more intense. Some of them will be, but some will be bigger; and some will be longer lasting than they would have been 20 years ago. 

DICHRON: Looking back on 2005, when hurricanes and climate change became such a big issue … I’d forgotten that DCI Group was working for ExxonMobil back then, and got caught putting out a fake new release disguised as local news that said climate change was not affecting hurricanes. (See ExxonMobil commercial disguised as local news below)

But if the discussion had been much more honest about how climate change was altering hurricanes, do you think we’d be addressing climate change more aggressively today with legislation? Or do you think it’s just the messiness of science? 

TRENBERTH: It’s partly the messiness. The understanding and the theory about the role of hurricanes in the climate system was at a very rudimentary stage back then. Even now, if you ask 100 scientists, I don’t think you get the right answer from more than about five. But my article in Scientific American in 2007 has stood up very well.

DICHRON: I see.

TRENBERTH: A lot of this still is being established. And many scientists still think only in terms of hurricane intensity. 

DICHRON: And these other factors such as size, longevity, and rainfall, as well as intensity, are what determine how destructive these storms will be.

TRENBERTH: If you are right on the coast, you should be incredibly worried about the intensity and the storm surge. But if further inland, you’re worried about flooding from rainfall. And one of the most robust things has been the increased flooding and rainfall with these storms. They all seem to have a lot more rainfall now. 

In my retirement, I’ve written a book which is coming out in Cambridge University Press to explain how the heat we are adding to the climate system is causing changes across the planet. And I have a memoir that goes into all the political controversies and the climate deniers.