Earth & Environment ︱ Dr Gary Yohe Climate change 40 years on the front lines of the climate change wars

ary Yohe specialises in Over the course of his long career, Yohe Gary Yohe, a Professor of Prof Yohe outside ’s show, Prof Yohe has given multiple talks Economics and Environmental Microeconomic theory, Natural has posed the following key pointers: the Rap Guide to Climate Chaos. and testimonies on climate change. Studies at the Wesleyan GResources, and Environmental 1. Why a change in approach is needed University has been on the Economics. As well as his research on - because carbon dioxide and other front lines of climate change the economics of climate change and greenhouse gases are not your reasonably be anticipated to endanger of one particular species - humans. Using includes both adaptation and mitigation research for the last 40 years. integrated assessment modelling, he has typical pollutants. public health or welfare”. That decision this expanded range of metrics revised and takes into account climate change This is an overview of his edited books like ‘Avoiding Dangerous 2. Reasons for concern – because implied that carbon dioxide – the most perceptions of how climate change is damages, co-benefits, sustainability, influential work on climate Climate Change’ (Schellnhuber et al, monetary value is not the only way important greenhouse gas – could be analysed by scholars and perceived equity, and attitudes to risk”. change risk management, 2006) and ‘Microeconomics: Theory to calibrate risk. treated as a pollutant under the Clean by decision-makers - making it much adaptation, mitigation, and Applications’ (Mansfield and Yohe, 3. Iterative risk management – looking Air Act. Carbon is no ordinary pollutant. more realistic in terms of how the world These sentences changed forever the detection and attribution. 2003). He has been involved with the at both adaptation and pollution Like methane and other heat-trapping really works. way that decision-makers across the United Nations Intergovernmental Panel mitigation through a lens that gases, it is different from other more planet look at climate change. The on Climate Change (IPCC) since the focuses attention on both likelihood familiar atmospheric or water borne ITERATIVE RISK MANAGEMENT days of claiming that the planet was not mid-1990s, and was a senior member of and consequence. pollutants. These pollutants are not Yohe considered that bringing risk warming were over. And cost-benefit the IPCC when it was awarded a share 4. The meaning of consensus – which regional, contemporaneous, or easily management to the fore was (in his mind analysis could no longer be used as the of the 2007 Nobel Peace Prize with Al does not mean universal acceptance, controllable; nor are their consequences and many others) the most important only approach to a policy debate. It Gore. Yohe was a member of the New but rather applying a carefully crafted reversible. Rather they are global, do conclusion from any IPCC report took many years for Yohe and his varied York (City) Panel on Climate Change double negative agreement that there not respect social, economic or political assessment. He was right. These were, colleagues to get widespread recognition and the standing Committee on the is no reason that any participant in boundaries, and their effects extend well and still are, the 30 most important words for this conclusion across the globe, Human Dimensions of Global Change of various meetings and collaborations into the distant future. Greenhouse gases authored by the IPCC (Bernstein et al, but it happened. the National Academy of Sciences. He would object to any word, number, therefore require large collective actions was also vice-chair of the Third National graph, or figure across a wide range over centuries. Climate Assessment under the Obama of not-implausible scenarios of how Yohe’s work measures the impacts Administration. the future might unfold. While the IPCC initially applied cost- of climate change ... using metrics such 5. Detection and attribution – it is not benefit analysis approaches to this Yohe’s focus on climate change enough to detect a risk – the source of pollution problem, one of Yohe’s key as species loss and human life loss. started in the early 1980s when that risk has to be clearly identified and contributions was his collaboration with he was invited by William the size of its effect or consequences many others on the creation of “Reasons 2007, pg. 22). Notice that they, too, were DETECTION AND ATTRIBUTION Nordhaus to participate in a has to be rigorously quantified. for Concern (RFCs)” in Chapter 19 of from 2007 (a seemingly historical high It has been known for at least two National Academies Panel on that topic, 6. Sea-level rise – a simple risk where the Contribution of Working Group Two point). That Synthesis Report concluded decades that climate change has at a time when globally only ten or so it is easiest to detect a manifestation to the Third Assessment of the IPCC that global warming was “unequivocal” advanced beyond the point where economists had any knowledge of the of climate change and conclude (Bernstein et al, 2007). There, he and his with human emissions of greenhouse mitigation alone can solve the problem. issue. His initial work created “spaghetti attribution that can be widely reported colleagues spelled out five reasons for gases the primary cause, and that But decision makers still need to be able graphs” to depict a wide range of and accepted. concern about climate change, but only “Responding to climate change involves to attribute the risks that they observe possible carbon emissions scenarios. 7. Developing the determinants of two were fundamentally economic. The an iterative risk management process that to climate change given “confounding Since then, he has published more adaptive and mitigative capacities other three highlighted extreme events, than 190 scholarly papers, policy notes, – identifying key characteristics of risks to unique and threatened systems, and opinion pieces on climate change responsive behaviour while keeping and large-scale discontinuities; each mitigation from an economic perspective. unintended consequences firmly could be calibrated in whatever metrics in mind. were appropriate. Iterations of RFCs have Most recently, his ‘A Review of Discerning 8. The social cost of carbon – currency appeared in subsequent publications from Experts’ (Yohe, 2019) has attracted metrics are helpful – but only if they IPCC and various scholarly journals like

attention because of the insights he are applied carefully across a wide Proceedings of the National Academies Staehli/Shutterstock.com Bernhard presents from his experiences with the range of policy considerations. of Science and Climatic Change. His work IPCC. These insights were directed at has contributed to this legacy because it changing the way the world, and its CHANGES IN APPROACH measures the impacts of climate change decision-makers, should consider climate In 2007, the United States Supreme using not only monetary currency, but also Human emissions of greenhouse gases, like those produced by cars, were identified in 2007 as the change and climate policy risks. Court found that carbon pollution “may metrics such as species loss and the loss primary cause of climate change.

www.researchoutreach.org www.researchoutreach.org factors” like population growth that influence a particular risk in concert with climate change. Why? Because it Behind the Research is impossible to project future climate- driven impacts without understanding Dr Gary Yohe the causalities and correlations between markers like global mean temperature E: [email protected] T: +1 860-803-8670 W: gyohe.faculty.wesleyan.edu and non-climatic factors like population and, finally, detected risks (likelihood and consequence, remember). Research Objectives References

Prof Gary Yohe has, since 1982, dedicated his career to Schellnhuber, H.J., Cramer, W. Nakicenovic, N. Wigley, T., Yohe’s most widely cited paper (Parmesan climate change research. and Yohe, G. eds. (2006). Avoiding Dangerous Climate Change. and Yohe, 2003) provided a universally Cambridge University Press. {68} applicable and rigorously statistical Mansfield, E. and Yohe, G. (2003).Microeconomics: Theory approach to assessing confidence in and Applications. W. W. Norton and Company. {44} Prof Yohe (left) with Barbara (centre) Detail attributing any detected impact on any and (right), his mentor. Yohe, G. (2019). A review of Discerning Experts. Climatic natural system to human activity – a great 84 High Street Change. 10.1007/s10584-019-02472-z. {forthcoming} leap forward. It has helped the entire Portland, CT 06480 Bernstein, L., Bosch, P., Canziani, O., Chen, Z., Christ, R., Davidson, O., Hare, W., Huq, S., Karoly, D., Kattsov, V., climate change research community’s to mitigate. This list, that has been used But the SCC was never intended to USA Kundzewicz, Z., Liu, J., Lohmann, U., Manning, M., Matsuno, T., efforts to provide “forensic attribution” by researchers from around the world to estimate the efficient price of carbon (i.e., Menne, B., Metz, B., Mirza, M., Nicholls, N., Nurse, L., Pachauri, to dramatic extreme events – i.e., using Bio R., Palutikof, J., Parry, M., Qin, D., Ravindranath, N., Reisinger, statistical analyses of the percentage Professor Gary Yohe has devoted most of his professional A., Ren, J., Riahi, K., Rosenzweig, C., Rusticucci, M., Schneider, S., Sokona, Y., Solomon, S., Stott, P., Stouffer, R., Sugiyama, T., contributions of various factors in observed The days of using cost-benefit analysis life to climate change research. This focus started in the Swart, R., Tirpak, D., Vogel, C., and Yohe, G., Climate Change and experienced extreme weather events. early 1980s. Since then, he has published more than 190 (2007). Synthesis Report (for the Fourth Assessment Report of as the only approach were over. Risk scholarly papers, policy notes, and opinion pieces. Most the Intergovernmental Panel on Climate Change), Cambridge University Press, Cambridge, 2007. {85} SEA LEVEL RISE management was the way forward. recently, his review of Discerning Experts (#189 on his CV) Sea level rise and coastal zone has attracted attention because he supplemented that Parmesan, C. and Yohe, G. (2003). A Globally Coherent Fingerprint of Climate Change Impacts across Natural Systems, management is the perfect laboratory to organise their thoughts about resilience an efficient tax on carbon). A calculation volume’s thorough coverage of three case studies with Nature 421, 37-42. {58} examine adaptation and mitigation options and the ability to respond, includes: that supports that policy estimate needs to insights from his own research interests and his experiences Yohe, G. and Tol, R. (2002). Indicators for Social and Economic using a risk-management perspective in take account of the cost of mitigation – the with the United Nations Intergovernmental Panel on Climate Coping Capacity –Moving Toward a Working Definition of the context of detection and attribution 1. access to resources other side of the cost-benefit calculation. Change, various National Academies of Science panels Adaptive Capacity, Global Environmental Change12, 25-40. {53} issues. For example, Hurricanes Harvey, 2. availability of response options including America’s Climate Choices (www.nas.edu), the Tol, R. and Yohe, G. (2007). The Weakest Link Hypothesis for Irma and Maria (etc.) showed that strong human, social, and political However, estimates of the SCC do help to (U.S.) National Climate Assessments (he was a vice-chair of Adaptive Capacity: An Empirical Test, Global Environmental 3. Change 17: 218-227. {80} estimates of losses must be calibrated capital (#’s , , and ) measure the value of policies or programs the Third National Climate Assessment), the New York (City) 3 4 5 Nordhaus, W. and Yohe, G., “Future Carbon Dioxide Emissions in the metric that makes the most sense. 6. a decision-making structure that may reduce or increase carbon Panel on Climate Change, as well as multiple testimonies from Fossil Fuels” Chapter 2 in, Changing Climate, Report of It is here where the metric of currency is taking responsibility emissions as a side effect. One example is before the two branches of the U.S. Congress. the Carbon Dioxide Assessment Committee, National Academy shown to be most lacking – a human life is 7. an ability to separate signal from the increased mileage (CAFÉ) standards of Science, 1983. {10} a life is a life. With the evolution of Yohe’s noise, and for automobiles – they increase mileage Collaborators work in coastal zones, it has become 8. a population that supported per gallon (increased fuel efficiency) and Prof Yohe has had many collaborators throughout his career. Personal Response apparent that we should prepare for a all of the above. reduce emissions of several greenhouse His mentors have been William Nordhaus, Thomas Malone, future that would prevent more extreme gasses including carbon. Calculations Alan Manne, and Stephen Schneider. How has the arena of climate change research changed violations of past conditions (by mitigating) Yohe and Tol proposed a “weakest of the SCC give a numerical value to be your career? as well as preparing to protect against link” hypothesis (Tol and Yohe, 2007) added to the benefits of (CAFÉ) standards William Nordhaus’s invitation to participate in an early previous records – even the historical worst -– judging the relative strength of in a cost-benefit calculation. National Academy of Sciences report on Changing Climate extremes in terms of damage. each factor and using the minimum to changed my life. It opened my eyes to an enormous frontier determine overall adaptive or mitigative So, cost-benefit analysis is still in of unexplored but fundamentally critical questions that were At this point, the risk-management capacity makes enormous sense. It has the game, but not everywhere. ripe for exploration from a rigorous economic perspective. Nobody in the early 1980s knew what those questions might approach asks, “How much insurance been a productive insight in planning be. Few knew what equations to write down. And so on… should we buy?” and “How can we adaptation and mitigation. The SCC achieved perhaps its most high- It was therefore important to work not only those questions, respond after an event that exceeds profile moment when Justice Sotomayor but also how to think about answers to the fundamental the boundaries of that insurance?” THE SOCIAL COST OF CARBON participated in a three-judge panel questions – carbon is not a familiar pollutant, Reasons for to communities who have seen those The social cost of carbon (or SCC) that decided that carbon dioxide was a Concern expand the calibration of damages, iterative risk questions before. estimates the “marginal” damage pollutant. The automobile industry took management is a key for all of those calibrations, but risk caused by adding another ton of that decision to the Supreme Court. In and iterative are the most important words, attribution is more important than detection of risk, understanding ADAPTIVE AND carbon emissions in a future emissions a 5-3 decision authored by Chief Justice capacities to adapt or mitigate is very challenging, and the projection. As a currency metric, it Roberts, the Court agreed that carbon MITIGATIVE CAPACITIES social cost of carbon tries to summarise complexities that Yohe’s work with others (e.g., Yohe and was the foundation of the Supreme dioxide fell under the Clean Air Act as cannot be calibrated – but it is the best that we can do to Tol, 2002) has helped to identify the Court’s 2007 decision to classify carbon a pollutant. Without the considerable calibrate the carbon effects of policies and programs that following list of underlying determinants of dioxide as a pollutant so that the Clean research of Yohe, such rulings could have are directed towards non-climate goals. decision makers’ capacities to adapt and Air Act applied. been a lot more difficult to achieve.

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