American Scientist

Atmospheric scientist Ben Santer is internationally recognized for his contributions to climate science, including the historic conclusion of the Intergovernmental Panel on Climate Change report in 1995 of the “discernible human influence on global climate.” His research at Lawrence Livermore National Laboratory focuses on evaluating climate models, using statistical methods in climate science, and identifying “fingerprints”—both natural and anthropogenic—in observed climate records. He is the recipient of the 2019 Sigma Xi William Procter Prize for Scientific Achievement, which has been annually awarded since 1950, with past recipients including conservation biologist Stuart Pimm, nuclear chemist Darleane C. Hoffman, and paleontologist Stephen Jay Gould. American Scientist’s Robert Frederick spoke with Santer about the current state of climate modeling, ongoing challenges, and what he finds encouraging.

To what extent has climate modeling changed in the past few years?

Overall, we now have much more complex models of the Earth’s system than we had when I started off in this field 35 years ago. Back then, we had relatively simple models of the atmospheric general circulation including very simple models of the upper surface of the ocean, which was essentially treated like a swamp. There was very little representation of the complexity of the full ocean general circulation and how the ocean interacts with the atmosphere. Now, we have these models that capture not only the three-dimensional circulation of the atmosphere, the oceans, and their interactions, but also sea ice, carbon cycles, ocean biogeochemistry, and atmospheric chemistry. In the next assessment reports of the Intergovernmental Panel on Climate Change, we’ll even have three-dimensional ice sheet models: Think the Greenland ice sheet and the Antarctic ice sheets, and the interactions between those ice sheets and a warming climate and a rising sea level.

These new Earth system models are amazing tools for trying to understand the complexity of the real-world climate system, particularly these interaction terms—between what we’re doing to the climate system by burning fossil fuels, increasing heat-trapping greenhouse gas concentrations in the atmosphere, warming, and increasing sea level, for example. So how is increasing the sea level, say, affecting ice shelves that are floating and holding back some of the Antarctic land ice that would otherwise be free to flow into the southern oceans and raise sea level further? We can study those kinds of interaction terms now with these Earth system models that have integrated ice sheets in a way we could not previously. That is huge, because arguably one of the biggest impacts of human-caused climate change is going to be felt through sea-level rise. We urgently need to better understand ice sheets on the move and—as we warm the planet’s climate and start melting these big ice sheets—how rapid and how large their contributions to global mean sea level will be. That’s a big uncertainty and something we urgently need to understand. We have a better shot at understanding that now with these integrated three-dimensional ice sheet models in full climate models.

Overall, it sounds like there’s somewhat of a computing—or even a big data—problem.

Absolutely, because these complex models of the Earth system generate enormous volumes of data. For the next assessment report of the Intergovernmental Panel on Climate Change—the sixth assessment that is due out in a couple of years from now—we’re looking at petabytes of simulation output. That’s providing scientists around the world with information about every aspect of the climate system they might care to analyze. How do you extract meaning from those enormous data sets? How do you boil them down into some parsimonious set of patterns and time series that capture most of the information in the data set and that tell you about some of these interactions between atmosphere, ocean, carbon cycle, and ice sheets? How do you do that? Clearly, this is not just the domain of climate scientists, but also the domain of statisticians and mathematicians and computer scientists, who are very comfortable in this world of enormous volumes of data and extracting meaning from very large data sets. That’s one of the reasons I’m fortunate to work at Livermore. We have excellent computational support and we, as climate scientists, routinely collaborate with folks who are trained as computer scientists.

In all of this, what encourages you?

About climate modeling, or about the future of humanity? [laughs]

How about “the future of humanity”?

Over my scientific career, I’ve witnessed the emergence of some human-caused warming signal from the background noise of natural climate variability. That was controversial nearly 25 years ago at the time of the finding of the second report of the Intergovernmental Panel on Climate Change, in 1995, that “the balance of evidence suggests a discernible human influence on global climate.” But now it’s incontrovertible that humans have changed the chemical composition of the atmosphere—by burning fossil fuels, primarily—and that those human-caused changes in chemical composition of the atmosphere have changed our planet’s climate. Back then, one of the points of criticism—justifiable criticism of the discernible human influence finding—was “You folks are looking only at surface temperature, at surface thermometer measurements of the Earth’s land and ocean temperature. If there really is a human-caused climate change signal lurking in observations, prove it to us. Look not just at temperature, but go beyond temperature. Look at the amount of moisture in the atmosphere. Look at the extent of snow and ice. Look at circulation patterns. Look at many other things: clouds, continental-scale runoff, snow pack, extreme heat, the properties of extreme events, intensity, frequency, duration. Convince us that this signal is not limited to surface temperature alone.” And that’s what’s happened in the intervening years since the “balance of evidence” finding in 1995.

Climate scientists have examined literally dozens of different aspects of climate change, using a wide variety of different measurement systems and platforms: Think space, think ground-based, think LIDAR [light detection and ranging], think weather balloons, think these beautiful Argo [robotic] floats that are dropped into the ocean and then go down to 2,000 meters and phone home when they get back to the surface with their temperature and salinity measurements. All of this stuff shows that there’s a signal, and that humans are largely responsible for that warming signal in the climate system.

So it’s that scientific confirmation that is encouraging?

The thing that makes me optimistic is that, in tandem with that scientific understanding of the reality of the human-caused signal in the climate system, we’ve moved on in the public arena. The public debate today here in the United States seems to be not “Is there a warming signal, are humans affecting the climate?” but more, “What do we do about it, and how do we respond, and what sort of economic and political options do we have to address this problem?” Voices arguing that nothing is happening, I would say, have little credibility in today’s world, given this overwhelming evidence to the contrary. And certainly that’s true internationally as well. If you want to stand up in Europe or in small islands in the Pacific or in Alaska or in Greenland and say that “nothing is happening,” it’s a tough sell when reality tells the opposite story. So that makes me optimistic: that over the past 25 years we have learned that the problem is real and ultimately we need to confront it and we need to deal with it.

It also makes me optimistic that there are these young folks who are flexing their muscles. Look at Greta Thunberg. Look at many of her peers who are recognizing that this is their world, too. They will have political power to decide who governs us. They understand this is our world and it’s being affected in a bad way by our actions today. That’s unstoppable. Then you have the economics of things: The cost curve for solar and wind is coming down dramatically, to the point where those forms of energy generation are now cost-competitive with many forms of fossil fuel energy. We also have the development that— despite the decision of the current administration to initiate the removal of the United States from the Paris Climate Accord—cities, states, companies are saying, “We’re in.” We recognize that we need to address this problem and that there are economic opportunities inherent in this problem. If we find cheap, efficient ways of providing low-carbon energy, we will be the economic leaders of the 21st century. The economics, the growing power of young people finding their political voices, the growing public awareness of the reality and seriousness of climate change—all of that makes me optimistic about our collective future.

Not just climate scientists, but politicians, the public, voters—you name it—everyone has some say in that debate about the kind of world in which we want to live.

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You’re getting a lifetime achievement award for your work. What’s in your future? Are you going to keep at it?

Absolutely. I’m an old dude now. I’ve had some opportunity to reflect about the past 25 years, after the “discernible human influence” finding, and to reflect also about where I want to go, what I still want to achieve in whatever amount of time is allocated to me. I remain deeply committed to doing this kind of work. My job is to fingerprint the climate system: to try to separate human-caused signals from the rich, natural variability of the climate system month to month, year to year, and decade to decade. That work is engrossing. It’s exciting. I get great joy out of working with younger scientists and trying to mentor them, trying to help them communicate better about the work that they do. I want to continue with that work for as long as I can. On the other hand, I increasingly feel that science is under attack. Climate science particularly is under attack. There are folks who argue in Congress that we don’t need to do this work and that it’s a hoax, a conspiracy, or that it’s something that scientists do in order to feather their own nest or to alter world systems of government. In my opinion, it’s critically important to push back against those kind of forces of unreason. We need science. We need data. We need facts in order to make intelligent decisions on how best to respond to the problem of human-caused climate change. So what do we do? How do we address the problem? Not just climate scientists, but politicians, the public, voters—you name it— everyone has some say in that debate about the kind of world in which we want to live. But if we’re trying to make those decisions based on misinformation or disinformation or wild zany theories, we’re all going to lose. That’s not helpful. So part of my job, increasingly, is to try to provide that sound scientific information to the public, so that all of us can make more informed decisions on what to do about it. It’s not good enough just to go to my office, close the door, publish a new paper on climate fingerprinting, and hope that somehow, magically, the information from that research will disseminate into the public arena and people will do the right thing. [laughs] I thought that way maybe 35 years ago. I don’t think that way now. It’s critically important to defend the technical work that you do, to explain what you do and why it matters and why other people should care about it. I want to continue doing that as long as I possibly can.

A podcast based on an audio interview with Ben Santer: