Climate science has from its very beginnings been a wonderfully multidisciplinary endeavor, encompassing biology, chemistry, history, paleoclimatology and, yes, physics. Fluid motion, thermodynamics of air and water, radiative transfer and the movement of the Earth on its orbit around the sun are all fundamental components that give rise to the complexity of the weather and climate system. But topics beyond physics also are key for understanding how life and climate have co-developed on Earth and how they might change in the future. Because of that multidisciplinarity, I had always assumed that climate science would never attract the attention of the discipline-based Nobel Prize committees.
Sure, the 1995 Chemistry prize awarded to the atmospheric chemists Sherwood Rowland, Mario Molina and Paul Crutzen for their work on ozone depletion could be considered climate-adjacent. But the two prizes explicitly related to climate change were the 2007 Peace prize, given to the IPCC and Al Gore for their efforts to communicate climate science to the public, and the 2018 Economics prize, awarded for work placing the science in an economics context, rather than for the science itself.
I was therefore shocked that this week the Nobel Committee for Physics acknowledged the tremendous advances we’ve made in understanding the climate system, awarding half this year’s prize of 10 million Swedish kronor ($1.1 million) to two climate scientists, Syukuro (Suki) Manabe and Klaus Hasselmann. Both were deserving of the award, but in such a collaborative field, other pioneering scientists are inevitably left out.
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These two scientists are representative of two main themes in climate science: the development of predictive, physically based climate models, and the detection and attribution of climate changes. Together these advances have allowed us to understand the climate changes of the recent past and make skillful predictions of our climate future.
Our ability to skillfully predict climate change dates from the 1960s with the development of global energy balance models, then one-dimensional radiative-convective models and later still fully three-dimensional climate models. The main conceptual advances occurred in the 1950s, 1960s and 1970s, while subsequent work has used increasing computational power to put those concepts into practice with ever greater levels of completeness and detail.
Among the many outstanding papers from that earlier era, one stands out. The 1967 work by Manabe and Richard Wetherald, published in the Journal of the Atmospheric Sciences, has been called the “most influential” paper in climate science. In it, they described for the first time the impacts of increasing carbon dioxide in a radiative-convective model that captured the fundamental aspects of the atmosphere thought of as a vertical column. Notably, it predicted the right amount of warming at the surface, recognized that the troposphere (the atmosphere’s lowest layer) would warm coherently, predicted the change in the height of the tropopause (the boundary between the troposphere and stratosphere) and, somewhat counter-intuitively, predicted that the stratosphere would cool. That vertical pattern of change is what Hasselmann, writing in 1979, would describe as a spatial fingerprint of change that was distinct enough from patterns of internal variability in the Earth’s climate that it could be used to detect the greenhouse gas signal in observations. That detection was first claimed in the late 1980s by James Hansen and colleagues and was reinforced through the 1990s and beyond.
But the Nobel committee is conservative. For many recent awards, the theoretical or conceptual breakthroughs have only been recognized when the predicted phenomena were unequivocally measured. The 2017 prize for the work on gravitational waves recognized the breakthroughs of Ray Weiss and Kip Thorne in the 1960s and 1970s, only after the LIGO teams had detected the waves in 2015. Similarly, Peter Higgs and François Englert split the 2013 prize for the 1964 predictions of the eponymous Higgs boson only after it was finally detected at CERN in 2012. In both of these cases the detections were announced once those signals were above what is called the five-sigma threshold (meaning a roughly 1-in-3.5 million odds that the signal arose by chance).
Climate predictions too can only be evaluated after a number of decades. Indeed, the work of Hasselmann can be used to assess exactly how long you need to wait to detect a specific rate of climate change. For current rates of change (about 0.2 degree Celsius per decade), two decades or more are needed. An assessment of those early predictions, published by Hausfather et al. in 2019 (and on which I was a co-author), included two early predictions by Manabe (1970) and Manabe and Ronald Stouffer (1993). We found that with only a couple of exceptions, these early attempts were remarkably successful at predicting the course of climate over the subsequent decades.
We need to remember that the Nobel Prizes have two important conditions: that there are no posthumous awards and that they cannot be shared by more than three people. This causes a problem when it comes to recognizing group efforts from 40 years ago. Indeed, of the predictions from the 1970s that we assessed, all of the authors who are eligible have now received Nobel Prizes (Suki Manabe and William Nordhaus)! It is a sad corollary that many of the pioneers are no longer with us. Norm Phillips, who built the first global climate model in 1955, died in 2019; Akio Arakawa, whose numerical techniques are the basis for all of the these models, died earlier this year; Richard Wetherald, Manabe’s co-author died in 2011; J. Murray Mitchell in 1990, John S. Sawyer in 2000, George S. Benton in 1999; all of whom made similarly successful predictions around the same time.
This progress in climate modeling has been distinct from, but related to, work in weather forecasting, which is perhaps an even more heavily physics-based endeavor, and one for which no Nobels have yet been awarded. Arguably the practical benefits from skillful weather forecasts far outweigh the benefits (so far) from our understanding of climate change. But this area, too, has perhaps too many individual contributions spread over too many years for the recognition to come through the Nobel process.
One last point: remember the detection threshold for the gravitational waves and the Higgs boson? Well, for the anthropogenic climate signal in surface temperatures, the five-sigma threshold was passed around 2012. Indeed, it has now exceeded seven-sigma (1-in-800 billion odds of happening by chance). That heuristic would suggest the climate science Nobel nod was about a decade overdue, but it is welcome nonetheless.