What was your path into climate science?
I always had this curiosity about the natural world. That was true from a very early age. When it came to graduate school, I was studying theoretical physics and was very much on the physics and math track. It was only when I was halfway through my Ph.D. at Yale University that I decided that my heart wasn’t really in the problems I was being given to work on.
So I started looking elsewhere on campus to see what else was going on and saw that there was a professor in the Department of Geology and Geophysics, Barry Saltzman, who was using math and physics to model Earth’s climate system, and that sounded like a really interesting, big-picture problem where I could use the math and physics knowledge that I had to work on something that really matters.
My Ph.D. research focused largely on natural climate variability, not on climate change. And it’s only because of some forays that we made into the analysis of paleoclimate data proxies—like tree rings, ice cores, corals, and sediments—that the work ultimately led to these pretty deep implications for human-caused climate change—the hockey stick—and our findings regarding how unusual recent warming is in a long-term context.
Once we published the hockey stick in the late 1990s and that became this sort of iconic graph, I found myself at the center of the raging climate debate. And so it was this almost accidental career path that led me there, but, as you probably gathered, I’ve come to embrace the role and the opportunity that provided me to participate in this larger discussion.
You are known for being vocal and really taking on climate deniers. How have you found the fortitude to face that kind of scrutiny and even hostility in some cases?
I’m just glad I’m not a public health scientist! [laughs] I say that jokingly, but, in fact, you know, I’ve developed some friendships with scientists in in the public health arena who have been involved in the public messaging on COVID-19. They’ve been subject to the same exact kinds of attacks as the climate community because of the inconvenient nature of their findings to certain vested interests or to certain ideological communities.
And it goes back much further than that. Paul Ehrlich, Rachel Carson, scientists before me were attacked because their message was inconvenient. I consider myself privileged to be in this long lineage of scientists who have found themselves in that position. Understanding that historical context and knowing that there are powerful interests that would like to shut us up provides me with fortitude, absolutely.
Honestly, if they had let me alone I probably would have remained in the lab, spending all my time analyzing data, building models, and crunching numbers. I probably wouldn’t be doing what I’m doing today. So in a funny and odd way, I thank my detractors.
Your research involves both observational studies of the climate as well as climate modeling. How are you pursuing those areas in your scientific work here at Penn?
The work we’re doing now falls very much in those categories. Judit Carrillo, a postdoc in my lab, is working on modeling the climate system. One of the things we want to understand is the factors that have driven the coming and going of the ice ages over the past million years, because it has implications for our understanding of this stability of the Greenland ice sheet and the Antarctic ice sheet today. There’s an obvious implication for climate-change impacts such as ice sheet collapse and sea level rise. But there’s some really interesting fundamental physical science to be done there as well, and that’s what we’re working on. My graduate student Chris Larson will probably be focusing on the specific role of the Greenland ice sheet.
Then with my other postdoc, Xueke Li, we’re continuing with a line of inquiry that began several years ago through a collaboration that I have had with scientists from Germany. That entails working toward understanding the impacts of climate change on extreme weather events and, in particular, some of the physics that we think is not well captured in current climate models that could be leading to an even greater impact on extreme weather events than the models predict.
One specific area of interest is nor’easters, coastal storms like the one that chilled the mid-Atlantic in early January 2018 and the infamous ‘Snowmageddon’ storm that left me holed in at a hotel off Rittenhouse Square when I was supposed to have given a talk at Penn in early February 2010. (Penn was closed down for three consecutive days and the interstates were closed.) These unusual storms feed off the relative warmth of oceans in winter and have some “tropical” characteristics. We’re interested in how climate change may be intensifying these storms, causing both heavy snowfalls and bitter cold temperatures from very strong northerly winds as the storm passes by.
In the past, journalists covering extreme weather events like hurricanes or other storms were careful to say that we can’t conclusively tie an individual event to climate change. Do you feel like that sort of statement is no longer valid?
Two summers ago I coauthored an op-ed in The New York Times with my colleague Susan Joy Hassol, the title of which is ‘That Heat Dome? Yeah, It’s Climate Change.’ In other words, we can now attribute events to climate change. It’s a statistical connection, but so is the connection between smoking cigarettes and lung cancer. The increase in occurrence is so great that we essentially attach a causal connection.
And when we say these extreme events wouldn’t have happened in the absence of human-caused warming, that doesn’t mean that there wouldn’t have been an extreme heat event—there might very well have been—but the magnitude and impact would not have been as great without the exacerbating effect of human-caused climate change.
What is the landscape of the research you’re doing in your secondary appointment at Annenberg?
We are excited to have just hired three postdocs and a research fellow in the science of climate communication to our center, in collaboration with the Annenberg Public Policy Center. We’re interested in identifying misinformation and disinformation and finding productive ways of addressing it. We’re excited about working with people like Emily Falk, who uses cognitive science to understand how ideas spread, and of course Kathleen Hall Jamieson, who, as the founder of FactCheck.org, has really been at the center of studying misinformation and disinformation for decades.
Doom and gloom and despair are increasingly a real obstacle to climate action and, in fact, are starting to replace outright denial as the main obstacle. So understanding those influences is critical. We’re currently conducting focus groups with Penn students to better understand the underlying phenomenon of ‘climate anxiety.’
The new center has also been very active. How is it making connections on campus and beyond on the topic of climate change and sustainability?
We’re aiming to serve both the University community, but also the wider community in Philadelphia. Some of the work we’re doing touches on issues of climate justice that are very relevant to urban environments like we have here. And we’re trying to address the larger public discourse about climate change and climate action.
With our lecture series, for example, we’ve brought in people from the policy community like the former Australian prime minister, Malcolm Turnbull, who is a political conservative but a climate advocate. We had U.S. Sen. Sheldon Whitehouse talk about the pernicious impact of dark money in our politics, with an emphasis on the obstacles to climate action. We recently hosted or participated in three Energy Week including an event with the Kleinman Center for Energy Policy and the Wharton School on the importance of environmentally-conscious investment. We’ve also participated in previous Climate Week campus events. We’re trying to take advantage of the amazing partners we have at Penn by supporting interdisciplinary conversations about the climate crisis.
You’re also teaching a course on climate change. Is that focused more on the scientific end of the issue?
Yes, but I focus on how and why it’s critical to understand the science to appreciate the other dimensions of the climate crisis.
Just today, in fact, in class, we were talking about flooding and climate justice. I discussed a study by Marshall Shepherd, a climate scientist at the University of Georgia. He has done some high-resolution studies of how weather systems interact with the urban environment in Atlanta, leading to an intensification of rainfall in certain locations in the city. And guess what? Those locations are all low-income. It’s low-priced real estate because it experiences more flooding. It’s not a coincidence. Climate science can help us better under climate injustice.
Let me also note that this study that probably wouldn’t have gotten done if not for somebody like Marshall, who is African American and considered it really important to understand this. It underscores the importance of diversity and inclusion in science.
Can you share a little about the book you have coming out this fall?
Yes, it comes out in September and is called ‘Our Fragile Moment: How Lessons from the Earth’s Past Can Help Us Survive the Climate Crisis.’ It’s taking me back to my science roots. The last book, ‘The New Climate War,’ was very much on the policy debate, the politics of climate action, and where we stand in that battle. But, while the book is really focused on the science, I do take on the topic of climate doomism, something that has been weaponized by bad actors to lead people down a path of disengagement, to convince them it’s too late. A lot of good people have been taken in by that framing: It’s too late, we’ve triggered runaway warming and nothing we can do is going to stop it.
It turns out that such beliefs are based on misrepresentations of what the paleoclimate record tells us. So it’s important to understand the actual, best-available science and try to understand what it tells us. The paleoclimate record, if you look at it comprehensively, tells us that there is some resilience to the climate system, the natural mechanisms that tend to keep our planet within livable bounds. But it’s possible to exceed those limits. The challenge, now, is to stay within those limits—something that remains possible if we take meaningful action.
How does it feel to be at Penn now?
Frankly, I feel like a kid in a candy store. Penn is the right place for me to be at this point in my career, and not just because of my historical ties to the institution and the city (my grandfather, father, and uncle all went here). It’s because it allows me to bring all of my disparate interests together: My passion in still doing the fundamental science, but it’s also in communicating it and working with world-class people on the science, impacts, policy and ethical dimensions and communication challenges of the climate crisis. It feels to me that Penn is an institution that has collectively decided that it’s time to really elevate climate to the next level. It’s an exciting moment to be here, to be part of what I see as a University-wide effort to prioritize the defining challenge of our time.
