Q&A: John Mutter on Climate Change Science

Columbia University Press has just published the second in an Earth Institute series of primers on sustainability. (The first was on renewable energy.) Authored by Earth Institute professor John Mutter, Climate Change Science: A Primer for Sustainable Development covers the basic physics of planetary climate, and how it is shifting. It delves into everything from glaciers to hurricanes, and the fundamentals of both long-term trends and short-term weather. Mutter started his career as a geophysicist, but has since moved into broader pursuits. Among other duties, he directs the Earth Institute postdoctoral research program. Recently, we spoke with him in order to get a preview of the book.

Kevin Krajick: Why another book about climate change — who is this aimed at?

John Mutter: The book emerged from my co-teaching an undergraduate class called Science for Sustainable Development. Climate science takes up one fairly substantial portion of the class. Students have always asked if there is a book to support the lectures. The answer is that all books I know of cover far more than we do in class, or are far too detailed on specific subjects and/or require more math preparation than the average undergrad in our class has acquired. So the main audience is undergraduates, especially those with little science background. By intent, it does not cover all of climate science, just essentials. It focuses mainly on what we need to know to be able to predict future climates — a big enough subject in itself. I hope it will be useful to some masters and even PhD. students.

KK: This is a pretty compact volume about a complex subject. Challenge: If you were to describe the earth’s climate system in just 100 words, what would they be? 

JM: We think of climate as a range of typical weather conditions experienced in different places on our planet, and their effects on living things. It rains hard in the tropics, the deserts are dry, wind blows hard one direction in some places, equally hard in the opposite direction in others places, and hardly at all in others. It is primarily an atmospheric phenomenon. But it comes about by interactions between the oceans, the biosphere, land surfaces and the atmosphere. The interactions are dynamic and brittle. Small changes can have large consequences. The primer provides an understanding of how these physical patterns arise. Climate as a determinant of human well being is a vastly more complex subject, but that first requires that we know how climate works.

KK: I think that’s about 125 words, but OK. What are the main unknowns about climate?

JM: The effect of clouds, specially cloud radiative feedback. Some clouds have a cooling effect, others a warming effect. As the world warms, evaporation of ocean waters will occur, and that will bring more clouds — that’s where clouds come from. Low clouds tend to have a cooling effect and counteract warming due to the greenhouse effect. These are the clouds that make you shiver at the beach. Very high clouds do the opposite — no shade, and a net warming effect. There is no consensus on which type of cloud will win out over the other. Another is the role of aerosols. These are tiny particles, not gases, in the atmosphere that on average cool the planet. But by how much is very uncertain. Both of these are critically important to understand how the earth will respond to greenhouse warming.

KK: People hear scientists talk about sea-level rise during this century of anywhere from 1 foot to 4 feet, or even more. Does this mean scientists don’t know what they’re talking about?

JM: There are two parts to this. When liquid water warms, it expands and takes up more space. That causes sea level rise, and it has been happening for a while now because of solar heating. We are confident of how this works, and how much sea level rise that can cause. There is a little, but not much, disagreement among scientists. The other part is the rise due to the melting of grounded ice sheets. That is much less certain, since it is a dynamic process. Among other things, ice sheets can crack to their very base, permitting water to flow deep into the substrate of the ice sheet, which can accelerate melting well in excess of simple theoretical predictions. A huge effort is going into understanding ice dynamics at present.

KK: At one point when discussing future uncertainties, you say it’s unreasonable to choose the midpoint between two extremes as the most likely outcome — in other words, to assume an average between the least drastic and most drastic projections. Why is this a bad idea?

JM: It’s bad because the perverse nature of the climate system makes it more likely that the outcome of warming will be near the worst case than near the best case. It comes about from all the many feedbacks in the system. Some amplify warming, like high clouds, and some counter warming, like low clouds. There are dozens we know about, and some we may yet discover. If all the many feedbacks add up to a net positive, then the distribution of outcomes becomes non-random or skewed, and the skewing is most likely going to be toward the worst-case outcome.

KK: How does climate change relate to sustainable development? Does it look different in poor countries versus rich ones?

JM: Development means improvement in the human condition. Sustainable implies that such improvement must be inter-generational. Everywhere the human condition is deeply dependent on climate conditions in any one place. Some places are much more habitable than others. In the tropics, where poverty is most concentrated and persistent, agricultural productivity is low and unpredictable. A change toward a warmer world will not only increase the ambient temperature; it will make the climate more variable, meaning more unpredictable. That will raise new challenges to agriculture, on which most countries depend for their economic well being.

KK: As a result of your evolving expertise, have you changed your lifestyle or taken other personal actions to address climate and sustainable development?

JM: I am a seismologist, but I now think, write and read more about climate change than anything else. Not many scientists make such a big change. I no longer drive a car, but that is really just convenience. If I do get a new car, it would be electric. But as for individual actions, the fact is an individual can’t do much. It requires collective action at the level of heads of government. You can make sure your home’s energy comes from renewable sources. But you shouldn’t think that being careful about things like recycling — and I am pathologically careful — will make much of a difference. Mostly they just make us feel virtuous. The primer is just the facts, but I am a good way through a new book that I hope will be called something like “Talking sense about climate change — for a change — now that we know it’s real.” It’s intended for a more general audience. Hopefully it will have some effect.

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