Ann Arbor (Informed Comment) – Informed Comment is pleased to present below an interview with climate scientist Michael E. Mann, Presidential Distinguished Professor of Earth & Environmental Science at the University of Pennsylvania. He is one of my heroes. As a young scholar, he co-authored a key paper in which he and his colleagues presented a graph of historical average earth temperatures from the year 1000 to the late 1990s, which showed that temperatures were relatively steady, and even dipped sometimes to the cold side, from the time of the Holy Roman Emperor Otto III until that of President Grover Cleveland. But from the late nineteenth century, the graph showed, temperatures spiked upwards startlingly. The graph looked like a hockey stick on its side, with the blade and toe sticking up sharply from the shaft.
The graph, with its clear demonstration that our carbon emissions since the Industrial Revolution have created a powerful greenhouse effect, alarmed Big Oil and its political lackeys no end. They mobilized to harass Mann, and if possible to marginalize him and destroy his career with smears and dirty tricks. Needless to say, they failed, and Mann became a major voice of reason and science, helping all of us confront the climate crisis.
In fact, in my view he has taken on the mantle of the great Carl Sagan (d. 1996), the Cornell astronomer who became the foremost communicator of science to the public in the late twentieth century.
It is the subject of the following interview:
Juan Cole: Our Fragile Moment appeals to me as a historian because it looks back at the earth’s climate history during previous epochs so as to help us interpret our present. You point to times in the past when biological organisms have helped shape the earth’s climate. That is, scientists used mainly to look solely at physical phenomena like volcanic activity, sunspots, and the earth’s orbit to understand climate change, but it is now clear that our own Anthropocene may not be the first time living beings have reshaped the atmosphere and the climate. Could you tell us more about these episodes?
Also, in the book you refer to the Gaia thesis that the earth has remained hospitable to life in part because it has thermostat-like mechanisms that swing into play when it gets too hot or too cold. You also point to the proposed Medea principle, that earth can become prey to feedback loops that turn it toward climate extremes at some points. You suggest that both have operated in earth’s climate history. I was a little confused by this exposition, because I had thought that a Medea principle would refute the Gaia thesis. Could you explain more about how each may have operated in our past and what that means for our future? Are humans now the Medea principle?
Michael E. Mann: “It’s an important point. We are the first life forms who had the capacity to understand how we are impacting our environment, but life has played an active role in the Earth system for billions of years. As noted in the book, that role has at times been benevolent (the development of vascular plants allowed for more efficient carbon burial and a stronger stabilizing impact on Earth’s carbon cycle. But the rise of oxygen due to oxygen-producing photosynthetic bacteria 2.5 billion years ago caused a rapid drawdown of the strong greenhouse gas methane that had been prevalent in Earth’s atmosphere, sending Earth into a snowball state, and nearly killing off all life on the planet (life made it through the event by retreating to “refugee” like deep ocean hydrothermal vents). The lesson is that living things can have both a stabilizing and destabilizing impact on our global environment. We are the first organisms to be in a position to make that choice.”
Cole: The theory that the Chixculub meteor killed off most of the dinosaurs depends on the notion of a climate “winter,” i.e. that the impact threw up so much particulate matter into the atmosphere that the world was plunged into a few years of darkness and cold that killed off the large land animals that could no longer find sufficient pasturage. Carl Sagan theorized that a major nuclear exchange between the US and the Soviet Union would produce an analogous “nuclear winter.” I remember seeing him debate Henry Kissinger about this. Now that Russian President Vladimir Putin is speaking, once more, of tactical nuclear war, that debate has become relevant again. What is the scientific consensus nowadays about the possibility of a nuclear winter?
Mann: In my view, the consensus has strengthened, because we have far more elaborate and comprehensive models of Earth’s climate today than the more primitive models used in Carl’s day. Climate scientists such as Alan Robock of Rutgers University have done simulations using state-of-the-art climate models that validate Sagan’s basic premise of Nuclear Winter. Putin’s saber-rattling over the potential use of tactical nuclear weapons in his war on Ukraine is a chilling reminder that this threat has not gone away.
Cole: In the preindustrial era, say 1750, there were about 280 parts per million of carbon dioxide in the atmosphere, and as I understand it, the level fluctuated between 150 and 300 ppm throughout the last 800,000 years. That is, human beings evolved and developed civilization in relatively cool times. We are now heading toward a much hotter earth and are not sure what it will look like. Many observers have suggested that the mid-Pliocene Warm Period, about 3 million years ago, affords the best picture of what our era of climate change will look like. That was a period in which parts per million of carbon dioxide in the atmosphere were about 400, compared to an annual average of roughly 420.2 in 2023. Wasn’t most of Florida under water then, with sea levels about 30 feet higher? Wouldn’t this imply that the 60 million Egyptians in the Nile Delta are going to be inundated? That Bangladesh and Louisiana are doomed? Wouldn’t there be swathes of the earth where the wet bulb temperature (heat plus humidity) is so high as to be deadly to human beings? How long do you think it would take for these catastrophes to unfold? Can human civilization flourish in a neo-Pliocene?
Mann: It’s a great question, and one I dig into in some depth in the book. Without going into all of the details, it turns out to matter where you’re coming from. A warm planet getting colder (that’s what happened in the mid-Pliocene) or a cool climate getting warmer (that’s what we’re causing today). In the latter case, it probably takes a modestly higher level of carbon dioxide in the atmosphere to cause the melting of the Greenland ice sheet and the massive (probably 30 feet) sea level rise that comes with that. So this buys us a bit of a cushion, but probably not a big cushion. If we warm the planet beyond 1.5°C higher than the preindustrial average and, almost certainly, if we warm the planet beyond 2°C, then we might indeed be subject to such catastrophic levels of inundation. It really underscores the urgency of reducing carbon emissions now.
Cole: Your new book is underpinned by a philosophy of moderation. You are concerned to use sound science to refute the worst-case scenarios of the doomsayers. You also seem to suggest that we have the resources to confront the baked-in results of climate change so as to keep life bearable on most of the planet. The French philosopher and archeologist Pierre Teilhard de Chardin said that we may as well believe there won’t be a nuclear war, since believing it would simply paralyze us. Is that the sort of thing you are getting at? You often dismiss exaggerations by saying, “reality is bad enough.” Could you explain more about your philosophy of life, which seems to drive your public advocacy?
Mann: There are two things going on here. One, in my view the science has often been mis-stated to support a narrative of inevitability of catastrophic, civilization-ending warming. An objective review of the science doesn’t support that scenario. But it’s also true that doomism can be self-fulfilling, and for that reason isn’t very helpful as a philosophical outlook. If the science told me we were doomed, I would be forced, by the bounds of scientific objectivity, to say so. Fortunately, it doesn’t! The evidence very much supports the notion that we can prevent the worst impacts of climate change through urgent action. But the window of opportunity is shrinking, and we have not yet seen nearly enough action.
Cole: You seem optimistic that the world can get near zero carbon emissions by 2050. Although it is true that our emissions have leveled off at the moment, that outcome seems unlikely to me. What if we go to 800 ppm of CO2 in the atmosphere? Wouldn’t the historical analogy at that point be to the early Eocene hothouse, when there was no surface ice, seas were 150 feet higher, when there was substantial acidification of the oceans and maybe half of one-celled marine organisms were killed off? Doesn’t humanity have 30 years to choose between living in the Pliocene Warm Period of 3 million years ago and living in the Eocene Hothouse of 50 million years ago?
Mann: I addressed this question in my answer above above with respect to overly high estimates of the mid-Pliocene sea level. But in the final chapter, I use as an epigraph a quote from French writer Antoine de Saint-Exupéry, from his posthumous volume of reflections entitled Citadelle, translated to English: “As for the future, your task is not to foresee it, but to enable it.” I would say that characterizes my view here. As long as we have it within ourselves to prevent the massive additional release of carbon pollution and catastrophic warming of our planet, I refuse to accept that it is preordained we won’t. The laws of physics are immutable. The laws of politics are not.