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Worst-Case Economics: Extreme Events in Climate and Finance

Worst-Case Economics: Extreme Events in Climate and Finance

by Frank Ackerman
Worst-Case Economics: Extreme Events in Climate and Finance

Worst-Case Economics: Extreme Events in Climate and Finance

by Frank Ackerman


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In both climate change and financial crises, worst-case scenarios and disastrous risks are inescapable. Yet public policy often focuses on average or likely outcomes, minimizing the danger of extreme events. ‘Worst-Case Economics: Extreme Events in Climate and Finance’ explores the underlying causes and the remedies needed for the most serious climate and financial risks.

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Product Details

ISBN-13: 9781783087075
Publisher: Anthem Press
Publication date: 10/23/2017
Series: Anthem Frontiers of Global Political Economy and Development
Pages: 208
Product dimensions: 5.70(w) x 8.60(h) x 0.80(d)

About the Author

Frank Ackerman is an economist whose extensive research and writing focus on climate change and energy, environmental policy and cost-benefit analysis.

Read an Excerpt



Most of the time, there are no speculative bubbles bursting or financial markets crashing. The abrupt loss of millions of people's jobs, homes and retirement savings is not a frequent occurrence.

Most of the time, hurricanes are not battering Houston, Miami, New Orleans and other vulnerable places. It is rare for the world to reach a tipping point into an irreversibly worse climate.

It is quite likely that none of these worst-case events are happening on the day when you are reading this book, or at any other single point in time. But none of these disasters are improbable enough to ignore.

Financial and climate crises may look like an odd couple for combined discussion. While both involve episodic crises, their rhythms of instability are different. Financial crises are fast-moving, repeated and, over enough years, reversible. Climate crisis is slow-moving, cumulative and could become irreversible on any human time scale.

Yet there are also deep similarities. Both involve rare, costly extreme events, with risks of huge losses that individuals cannot escape on their own. Both are created by short-sighted human activity, pursuing immediate economic gain at the expense of long-term consequences. Both are misunderstood by conventional economics, which minimizes their importance and discourages the development of sensible public policy responses. And both face major industries with a vested interest in the status quo, a powerful obstacle to the adoption of policies that could prevent future crises.

This comparison of the two fields grew out of my research on the economics of climate change. In that research, an analysis of financial markets, focusing on the treatment of extreme risks, turned out to be remarkably useful in understanding potential climate outcomes. In both fields, there is a need for a new and better economics of risk and responses. Protection against both climate and financial crises requires policies that bear some resemblance to insurance, based on a new understanding of risk and innovative ways of thinking about decision making under uncertainty.

The goal of this book is to understand the patterns of extreme events and the policies needed to address the risks related to these events. How should we respond to the fact that high-cost losses in both climate and finance are not as rare as we might have hoped or expected?


The Great Recession threw almost nine million people out of work; US employment did not return to its 2007 level until 2014. And many who remained employed ended up with lower wages and/ or fewer hours of work than before. Youth unemployment was particularly severe, with long-term consequences for those who entered the labor market during the downturn. Research on prior years has found that those graduating from college during a recession experience significant negative effects on wages — effects that may last for as long as 15 years. Those who were already of working age during the Great Recession, meanwhile, are likely to have permanently lower retirement incomes, as their job losses and slower wage growth ripple through the formulas for future Social Security payments. For those who had been saving for retirement, the problem is compounded by the collapse in the value of homes and financial assets.

More than nine million households lost their homes between 2006 and 2014; many of them may never be homeowners again. House values fell by a nationwide total of $5.5 trillion; in 2011, 11 million households owed more on their mortgages than the current market value of their homes. Housing is the largest asset owned by most people, so the crash in house values had a devastating effect on wealth in general. Between 2007 and 2011, one-fourth of American families lost at least 75 percent of their net worth; more than half lost at least 25 percent. Losses were worst, in percentage terms, for low-income and minority households.

The United States has had numerous weather disasters for which the country was ill-prepared, including Hurricane Katrina drowning New Orleans in 2005, years of record-breaking drought in California, Hurricane Sandy clobbering the New York area in 2012, Hurricane Harvey inundating Houston in 2017 and floods along the Mississippi and other major rivers. Elsewhere in the world, the impact of extreme weather is even worse. The worst recent climate-related losses in high-income countries occurred in the European heat waves of 2003 and 2010, discussed in Chapter 6. Storm damage is proportionally greater, and resources for protection and recovery are more limited, in low-income coastal countries such as Bangladesh and the Philippines, as well as in small island nations that are threatened with complete inundation.

The cause of these climate trends is well known, even though individual events are unpredictable in detail. Rising greenhouse gas emissions, primarily due to combustion of fossil fuels, are warming the world and destabilizing the climate. Larger, irreversible damage could occur in the not-so-distant future, although the timing and magnitude of such threats remain uncertain. The direction of change, however, is clear: catastrophic climate losses, although still unlikely today, become steadily less unlikely as the world grows warmer.


Imprecise predictions of extreme events are no excuse for inaction. Ample warnings have repeatedly been ignored by policy makers. Four years before Hurricane Katrina, a detailed description of the vulnerability of New Orleans and the need for improved storm defenses appeared in Scientific American. Seven years before the housing, subprime mortgage and stock market bubbles burst, Robert Schiller, a prominent economist, published a widely cited book with a title that tells the story: Irrational Exuberance. Alongside the puzzling origins of extreme events, there is the mystery of why public policy remains feckless in the face of such well-anticipated harms.

Both climate and financial risks are misunderstood by the conventional economics of public policy. The policy choices of recent years have failed to provide adequate protection in either sphere. The Obama administration spoke eloquently about both financial and climate crises, but its actions only whispered. The Trump administration, if it understood French, could tweet "après moi le deluge," as it attacks the rules that restrain both financial fraud and global warming. Both the earlier, timid, and the later, destructive, responses reflect the power of corporate lobbies that oppose limits on speculative investments or fossil fuels. Theories that dismiss obvious risks, endorsing little or no response, are convenient for (and sometimes subsidized by) those who profit from the status quo.

In terms of solutions, this book argues that cost–benefit analysis, a standard tool of policy evaluation, is not a useful approach to policies addressing extreme risks. Among other limitations, this type of analysis fails because for many extreme risks there is no such thing as a meaningful average or expected value, and because standard theories misunderstand, and badly underestimate, the importance of risk aversion. More appropriate alternatives call for more precautionary approaches to major risks. Decision making without numbers, the realm in which we inevitably find ourselves, calls for policies based on the credible worst-case outcome — an approach similar, though not identical, to the precautionary principle. In the very worst cases, when facing an existential threat, total mobilization of resources is called for; this approach is valuable when valid, but dangerously easy to abuse.


Economics matters, not only to economists. It has become the language of public policy, providing quantitative analysis and intellectual authority on complex political questions. The economics of policy debate, however, often relies on ideas that are simpler and more traditional than leading economic theorists now endorse. The old-time religion of free-market theory seems entrenched in the intuition and practice of politics in America and has powerful advocates elsewhere. Cost–benefit analysis, increasingly seen as a gatekeeper for policy approval, typically starts from the assumption that the current state of affairs is close to being optimal and sustainable. Risks of extreme events are often implicitly excluded in an approach that focuses on average or most likely outcomes.

Although it is no longer state of the art in research, naïve policy economics has a lengthy academic pedigree. The first part of this book explores the origins and limits of traditional economics. There have been other critiques of the subject, raising a number of the points discussed here. But to round out the understanding of what is wrong with conventional economics, two key features deserve greater attention. First, there is a tendency to dismiss extreme events — a blind spot that has been present ever since the nineteenth-century origins of the theory. Second, there is a growing disconnect between advanced academic and pedestrian policy-oriented styles of economics. Understanding public policy debates therefore requires looking back into the origins of the field.

In the beginning, in the 1870s, there was a powerful but flawed analogy to nineteenth-century physics, as explained in Chapter 2. Gas molecules collide, exchanging energy as they approach equilibrium; firms and households encounter each other in the marketplace, exchanging goods and services as they approach economic equilibrium. This analogy created the framework of economics as it was taught and thought about for much of the last century — and as it is often applied to public policy, even today.

The analogy to physics was never a complete success. Economic "particles" were assumed to be individuals following their own idiosyncratic preferences. This assumption created a satisfying story about political liberty. At the same time, it lost the rules-based predictability and simplicity of the comparable theory of the dynamics of physical particles. The final, rigorous form of Adam Smith's story of the invisible hand, which emerged in the mid-twentieth century, depended on at least three sets of unrealistic assumptions.

First, the marketplace was assumed to be populated by homo economicus, an imaginary species of completely asocial, selfish, perfectly informed and perfectly calculating individuals. In contrast, real people are inescapably social, incompletely informed and imperfectly rational, as discussed in Chapter 3. Broadly speaking, this helps to explain why there are so many individual and collective decisions that in hindsight appear wrong — in financial markets, in climate and environmental policies and elsewhere. But the ability to transcend selfish, asocial calculation is also part of the solution to our current crises: real people are capable of compassion, and of taking actions that benefit others as well as themselves.

Second, homo economicus inhabits an equally imaginary landscape, where goods and services are produced and sold by enterprises too small to exert any market power. Meanwhile, a problem-free natural environment provides fresh air, forests, tolerable temperatures and other services in abundance. It is a far cry from the modern world of inevitably large firms and pervasive pollution, reviewed in Chapter 4. Climate and financial crises are results of big and dirty reality and would not occur in a small, clean utopia.

Third, the original analogy to physics suggests that fluctuations in the economy, such as the ups and downs of financial markets, might follow a bell curve, or normal distribution. If this were true, it would paint a comfortably subdued picture of uncertainty, one in which extreme events are vanishingly rare and could safely be ignored. Chapter 5 looks at the bell curve and shows that it clearly does not fit the pattern of changes in stock market prices.

Chapter 6 introduces an alternative picture, known as the power law, in which extreme events are much too common to ignore. (In this picture, the probability of an event is inversely proportional to some power, such as the cube, of the magnitude of the event. Mathematical understanding of the power law is not required, except to note that it implies that dangerously extreme events can be dangerously likely.) This unruly picture of uncertainty provides a much better fit to the data, both in financial markets and in extreme weather events such as hurricanes and heat waves.


The second part of the book asks why extreme events are so common. As Chapter 7 explains, there are at least four possible explanations for the ubiquity of power laws. First, it could be simply a statistical artifact, an error introduced in data analysis. Second, as natural systems approach tipping points and phase changes, such as melting or freezing, these systems are known to "flicker" in a manner that displays power-law patterns. This could be important for climate extremes. Third, the sandpile story, a modern metaphor, suggests that some simple systems continually return to the edge of instability, with the resulting episodes of instability following a power law. Finally, the story of intermittency — such as the challenge of balancing a stick on your fingertip — leads to similar patterns, in a manner that may be particularly relevant to financial crises.

The next two chapters offer two independent explanations of extremes in financial markets. Either explanation could, on its own, cause the observed patterns of boom and bust. In Chapter 8, social interactions among traders — reflecting the ways in which real people do not behave like homo economicus — are enough to create recurring financial bubbles and crashes. Traders influence each other's strategies, which leads at times to waves of abrupt change. In this interpretation the instability of the market is analogous to the stick-balancing challenge, and the future will always bring another wobble, if not a fall.

Inequality alone could also explain financial instability, as seen in Chapter 9: the wealthiest traders cannot always avoid rocking the boat as they climb in and out of the market. In this story, extreme market outcomes simply reflect extreme concentrations of wealth, a well-known and longstanding pattern. Those concentrations of wealth call for some explanation: they would arise naturally in a different story about market interactions, a sociological theory of continual conflict over resources.

Climate risks are the subject of Chapter 10. Nature becomes fragile when pushed too hard in the wrong places, as the fossil-fueled economy seems determined to demonstrate. Numerous potential tipping points have been identified, points at which large, irreversible damages are expected to occur. Yet measurement of climate risks is constantly frustrated by "known unknowns." Unlike financial risk, which involves recurring events, the most serious climate risks center on the unknown likelihood of future one-time events. Despite this difference, similar questions arise in both fields about the probability of extreme outcomes. The timing and magnitude of climate risks remain unknown, although inaction makes the risks grow more severe. The early warnings of those risks are already more than enough to motivate immediate and vigorous measures to reduce carbon emissions.

Predator–prey models from biology offer a different image in Chapter 11, suggesting an analogy both for Hyman Minsky's theory of financial instability and for the economics of climate change. The asymmetric rhythms of predator and prey arise when debts devour incomes in Minsky's world, or when greenhouse gases in the atmosphere prey on output in climate economics.

Standard climate economics models often come with optimism built in, using a framework that rules out a climate-caused slowdown in productivity and growth rates. Newer research, finding that climate affects productivity and growth, predicts deeper, longer-lasting damages. The persistence of carbon dioxide in the atmosphere means that today's emissions will contribute to climate change far into the future. Thus, a crash rather than a continuing cycle becomes a likely result in the predator–prey picture of the fossil-fuel-burning economy.


The causes and the dangers of extreme events are not just matters of intellectual curiosity. The final section of the book turns to the appropriate responses, the approaches to public policy that are required in a world of worst-case economics.


Excerpted from "Worst-Case Economics"
by .
Copyright © 2017 Frank Ackerman.
Excerpted by permission of Wimbledon Publishing Company.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

Table of Contents

List of Figures; 1. Introduction; 2. Steam-engine economics; 3. Beyond homo economicus; 4. Big and dirty; 5. Pictures of improbability; 6. Trillions, or only hundreds?; 7. Zipf’s law and other stories; 8. Ants and traders; 9. Too big to ignore; 10. Climate tipping points and known unknowns; 11. Predators and prey; 12. Good enough for government work; 13. Fat tails and the failure of forecasting; 14. Misunderstanding risk; 15. Choices beyond calculation; 16. Who won World War II?; 17. Conclusion; Acknowledgments; Bibliography; Index.

What People are Saying About This

From the Publisher

“Old-fashioned economics has led to dangerously wrong-headed approaches to climate change and other ‘extreme event’ situations, such as financial crises. In this highly accessible but profound book, Ackerman persuasively shows the urgency of smarter, more recent thinking about how natural and economic systems work and why we need to pay much more attention to worst cases. This is a must-read book for anyone who wants to understand the world we now inhabit.”
—Juliet Schor, author of Plenitude: The New Economics of True Wealth

“Ackerman’s Worst-Case Economics will convince you that the conventional economic modeling of risk is inadequate when financial crashes, environmental collapse and other cataclysmic outcomes are possible and that policies based on prudence regarding the worst-case scenario are needed. An important book and a delight to read.”
—Samuel Bowles, Research Professor and Director, Behavioral Science Program, Santa Fe Institute, New Mexico, USA

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