06 Jan 2011: Analysis

Calculating the True Cost
Of Global Climate Change

Researchers disagree about what the economic costs of climate change will be over the coming decades. But the answer to that question is fundamental in deciding how urgent it is to take action to reduce emissions.

by john carey

When climate legislation died last summer in Congress, one cause was the powerful drumbeat of claims that the bill would bring economic disaster. The legislation would amount to a massive tax hike, devastating an already crippled economy and throwing more people out of work, charged Senator James Inhofe (R-Ok) and Glenn Beck. It would be “the final nail in the coffin of the American middle class,” proclaimed an ad from the Conservative Society of America. Despite supporters’ protests that the price tag of greenhouse gas curbs would be modest, voters’ fear of hits to their pocketbooks forced even many Democrats to backpedal.

The heated argument about economic costs, however, barely touched one vitally important issue: the costs of NOT taking action on climate. What if last summer’s Russian heat wave and drought, which destroyed one third of the country’s wheat crop, or the catastrophic floods in Pakistan and China, or category 5 hurricanes like Katrina are just glimpses of future havoc from warming left unchecked? As Kevin Trenberth, head of the Climate Analysis Section at the National Center for Atmospheric Research, observes, “Certain events would have been extremely unlikely to have occurred without global warming, and that includes the Russian heat wave and wild fires, and the Pakistan, Chinese, and Indian floods.”

The economic costs of such disasters could make even inflated estimates of the legislation’s price tag look small, says University of California, Berkeley, economist Michael Hanemann. Yet Congress didn’t seem to care. “The question of damages from climate change never penetrated the debate in
There’s a deeply rooted perception in the U.S. that the economy will suffer little damage from climate change.
Washington,” Hanemann says.

Why not? Partly, it was a conscious political calculation. Polls show that scare tactics work better to block legislation than to bring sweeping change. The Obama Administration and environmentalists decided to tout the clean energy industries that could be created and boosted by the climate bill, rather than warn of withered crops or drowned cities from heat and rising sea levels. “The assumption has been that focusing on short-term job creation would be a more compelling political argument,” says Dan Lashof, director of the Natural Resources Defense Council’s climate center.

More importantly, there’s a deeply rooted perception that the U.S. economy will suffer little damage from climate change. That view dates back to work from the mid-1990s by the influential Yale University economist William Nordhaus. Nordhaus took what was known about the science of climate change, then constructed an economic model to estimate the monetary harm. The model put the economic cost to the U.S. of raising global temperatures by 2.5 to 3 degrees C (expected by about 2100) at about ¼ to ½ percent of GDP. “There are both good and bad impacts, but they offset each other,” explains Robert O. Mendelsohn, professor of forest policy and economics at Yale University and a frequent collaborator with Nordhaus.

The original economic model wasn’t complete, Nordhaus readily acknowledges. It didn’t include some sectors of the economy or “non-market” damages — effects that economists can’t easily quantify, such as loss of species. “We basically guessed on those, and that got us up to between 1 and 2 percent of GDP,” says Nordhaus — still relatively small. Since then, Nordhaus has worked extensively on the analysis, but the general conclusion is the same. There’s little threat to U.S. GDP. “Do I think that the measured GDP of the U.S. or Britain or Japan is seriously at risk from global warming over the next 100 years?” Nordhaus asked in an interview. “No,” though he adds that “GDP is a poor indicator of economic welfare.”

Other experts see the hit to GDP as much greater. “We did a survey of top economists in the country, asking what they think about the costs and benefits of climate legislation,” says Michael Livermore, executive director of the Institute for Policy Integrity at New York University School of Law. “They said that climate change is a clear threat to America and the global economy.” Adds Berkeley’s Hanemann: “I don’t want to be Dr. Gloom, but our complacency in the U.S. is wrong.”

An earlier version of this debate flared into public view and the media for a short time in 2006. A report prepared for the British government by economist Sir Nicholas Stern found that the cost of unconstrained global
Top economists surveyed say climate change is a clear threat to America and the global economy.
warming would be huge — up to a 20 percent drop per year in the world’s GDP by 2050. The widely disparate conclusion compared to Nordhaus’, however, turned largely on one single factor: Stern put a higher value on costs far out in the future — and on the future return from climate change reduction investments made today — than Nordhaus did. Or in economists’ jargon, he used a lower discount rate. “You can change the discount rate and get a totally different answer,” explains NRDC’s Lashof.

Who’s right? The late climate scientist Stephen Schneider liked to ask economists if they really do value their grandchildren far less than their children, as implied by a higher discount rate. Nordhaus, who dismissed the Stern report in a 2007 book as “political in nature,” with “advocacy as its purpose,” says that’s not a fair comparison. “The argument is not how we value our grandchildren, it’s primarily about the return on capital,” he says. “My view is that the return on capital is high, so that the threshold is pretty high if we are going to compete with other uses of our investment dollars.” That makes efforts to fight global warming seem less cost-effective.

But the tiff over discount rates is really a sideshow. There are now new critiques of the low estimates of the costs of climate change that challenge core details of how those damages were calculated, such as whether the analyses correctly included the costs of heat waves, more intense hurricanes, and other extreme events predicted to become more common. The original work “has been enormously influential, but for a number of reasons, I think the analysis is profoundly wrong,” says Hanemann.

One issue cited by the critics is that the models assume that many of the costs of climate change in the U.S. are balanced by benefits — or that it will be easy to adapt. For instance, heat waves in summer mean higher energy costs and more deaths from heat. However, warmer winters save fuel and lives, so in the economic models, the two generally balance out. And sure, if temperature rises above 95 degrees F, corn pollination starts to fail. But defenders of the models figure cornfields could just move to cooler areas. “If you take adaptation into account, this turns out not be such a big effect,” argues Mendelsohn.

The critics say these conclusions are far too optimistic. Hanemann points out that summer air conditioning requires expensive daytime peak power, while the winter savings come from much cheaper nighttime baseload
‘The damages grow much worse as we get more extreme events,’ says one economist.
power. So the overall costs must be higher. Similarly, damages to agriculture from heat waves and droughts are likely to swamp benefits from milder winters and longer growing seasons — and moving crops to better climes may be costly or difficult. Nordhaus partly agrees. “The damages will differ by crop and by region,” he says. “I think the numbers will be large for some regions, such as those now bordering on desertification.”

The models also calculate future harms using predicted average increases in temperature or precipitation. But scientists don’t believe temperatures and precipitation will be uniformly average around the planet. Instead, they foresee more — and more severe — extreme events: more powerful hurricanes and storms, record floods, searing heat waves and droughts, bigger wildfires. In fact, the U.S. has already experienced a higher-than-average amount of warming. A graph showing these events would not only have a long tail (i.e. the events are more extreme), but the tail would also be fatter (i.e. more events). “The damages grow much worse as we get more extreme events,” explains Hanemann. “We need to pay more attention to the tail.”

Nordhaus says that his model doesn’t neglect the idea of extreme events. “It’s completely wrong to say we’ve ignored it,” he says. But even supporters acknowledge that not everything is in the models, including a full treatment of extreme events. “Nordhaus’ model was never intended to be the kitchen sink,” says Mendelsohn.

Critics say that’s a serious flaw. “Many, many of the costs associated with climate change are not included in the models,” says NYU’s Livermore. Additional examples include acidification of the oceans from the absorption of carbon dioxide, which could threaten ocean food chains; loss of glaciers, which could cause water shortages and reduce hydropower; sea level rise, which could flood coastal cities; and mass migrations and increased global tensions, as people move away from regions hit harder by of the effects of climate change. The military takes these possibilities seriously, noting that climate change is a “threat multiplier.”

Harvard economist Martin Weitzman even suggests that the economic costs of a catastrophic event, however unlikely it might be, would be so enormous that it would overwhelm the whole analysis. “Perhaps in the end the climate-change economist can help most by not presenting a cost-benefit estimate for what is inherently a fat-tailed situation with potentially unlimited downside exposure,” he writes.

True, the models don’t include all possible costs or catastrophes, Nordhaus and Mendelsohn respond. For one thing, the models calculate the damages
The costs of a catastrophic event would be so enormous that it would overwhelm the analysis.
from climate change only in terms of economic activity. They don’t assess damages from non-market effects like loss of species. Take ocean acidification, which makes climate change more worrisome than it appeared to be in the 1990s, Nordhaus says. The direct economic damages from acidification are negligible. “We know the actual economic impacts are almost sure to be small because they involve fisheries, which are already pretty small, and they involve only ocean fisheries that are sensitive to carbon,” Nordhaus says.

Similarly, the calculated damages from extreme events are small, Nordhaus and Mendelsohn say. While the estimated cost of Hurricane Katrina topped $150 billion, hurricanes don’t actually hurt the economy, as measured by GDP. “If your million-dollar house blows away tomorrow, it would not affect GDP,” explains Nordhaus. The reason: spending to rebuild stimulates the economy. “This is one of the ways in which GDP is a flawed measure,” Nordhaus adds. Mendelsohn has spent years trying to figure out what the additional damages from extreme events might be — and he argues that they don’t amount to much. “As long as we didn’t measure this number, the perception was that it was huge,” he says. “But when we actually measure it, it turns out not to be big.”

That assertion is a matter of fierce debate, however. The damages are far higher, Hanemann and others believe. In Hanemann’s analysis, the economic toll from unconstrained climate change in the U.S. is three to four times higher than Nordhaus’ model calculates.

Other new analyses have similar results. Livermore and his colleagues looked at the economic benefits of the Waxman-Markey legislation passed by the House of Representative last year, including the avoided harm from climate change, and compared those benefits to the price tag for the bill. “The benefits outweighed the costs by nine to one,” says Livermore.

The U.S. Environmental Protection Agency is also expected to conclude that inaction is costly. With climate legislation apparently dead, regulation under the Clean Air Act is the only remaining pathway to federal curbs on greenhouse gases. To bolster its case in the face of strong opposition, the agency is working on a more detailed analysis of the costs and benefits of regulation, sources say. Past Administration efforts to assess the economic toll used Nordhaus’ basic approach. But because of the limitations of the economic models, the agency is also planning to examine scenarios of possible climate change, and expects that it will find a large economic toll. “We think the costs of not acting will be huge,” says one EPA official.

Nordhaus acknowledges that the small hit to the GDP of rich nations from climate change predicted by his model is just part of the overall story. “I’ve been working on this a long time,” he says. “The facts have changed, and my view has changed.” For example, “emissions and temperatures are rising faster than earlier models thought and the geophysical impacts look more serious,” he says. So even if direct economic impacts are small, “ecologists and biologists have made a pretty serious case that other things are at risk,” he says. “I think the non-market impacts have turned out larger than I thought and what the community [of economists] thought.” Those non-market impacts don’t show up in the results of the economic models.

In addition, Nordhaus says he now has a greater appreciation for the unknowns, including potential catastrophes. “The uncertainties are enormous,” he says. “If you include them, you can say almost nothing about the second half of the century.”

A Positive Path for Meeting
The Global Climate Challenge

A Positive Path for Meeting the Global Climate Challenge
Climate policies that require public sacrifice and limiting economic growth are doomed to failure, writes Roger A. Pielke Jr. To succeed, policies to reduce emissions must promise real benefits and must help make clean energy cheaper.
Nordhaus’ own conclusion is that action on climate is needed, especially since his analysis also shows that the economic costs of reasonable policies are relatively small. Indeed, there’s no longer a debate among economists that action should be taken, says Mendelsohn: “The debate is how much and when to start. If you believe there are large damages, you would want more dramatic immediate attention. The Nordhaus camp, however, says we should start modestly and get tougher over time.”

Regardless of the role played by economists in the global warming debate, the view that climate change is not to be feared has contributed to the delay in the world’s response. Even Nordhaus says he’s “stunned” by the lack of progress in tackling climate change. “It doesn’t matter if I, or Weitzman, or Hanemann are right on this,” says Nordhaus. “We’ve got to get together as a community of nations and impose restraints on greenhouse gas emissions and raise carbon prices. If not, we will be in one of those gloomy scenarios.”

POSTED ON 06 Jan 2011 IN Biodiversity Climate Forests Policy & Politics North America 


Economists like Nordhaus have in the past given little sign that they understood the science of climate change and the enormity of what lies ahead for humanity if we don't rein in emissions. Stern has understood and accepted the science and made that the basis for his economic prescriptions (and been accused of political advocacy because of it). It sounds from this article that Nordhaus may now be taking the science more seriously. He needs to. It is the overwhelming reality and any economic prescription which delays urgent steps to drastically reduce emissions starting right now is out of touch with what is happening to the biosphere.

Posted by Bryan Walker on 06 Jan 2011

In this interconnected world, the notion that what affects the US GDP and standard of living is only what happens within the US border (and Nordhaus et al seem to forget the US includes Alaska, Hawaii, Puerto Rico, Trust Islands, etc.).

The global economy is interconnected, as the recent banking crisis made very clear, and the U.S. resource and trade footprint is very extensive, so what happens elsewhere will have an effect on the U.S. While this issue was not handled in the US National Assessment in 2000, we at least acknowledged that there are connections to the world that affect trade, investments, imported products, shared natural resources (water, migrating species, fisheries), human health (like initiation and spread of diseases), environmental refugee, moral concern for the well-being of others, biodiversity resources, national security, and many other types of connections--not to mention that there are Americans all over the world for many reasons and they too might care and be affected by the impacts.

The U.S. is not some isolated, independent island that can get by without being connected to the world--and as one of the very large emitters (cumulatively and year-by-year), to think that a devastated world around us will still be friendly is very wishful dreaming. To say that the calculations of impacts by Nordhaus and others are incomplete is really quite an understatement--any economic measure is going to be incomplete. In coming to the conclusion that 2 C should not be exceeded, the leaders of the world are drawing on a much broader set and view of impacts--as they should. A number of us think 2 C is likely too high if major impacts are to be avoided, but at least they recognize there is much more to consider than just the impacts on the GDP in their own countries.

Posted by Michael MacCracken on 06 Jan 2011

Damage estimates by Nordhaus, Mendelsohn and many others don't adequately include the increasing frequency of extreme weather events, which rise disproportionately when the average climate shifts. These extreme events actually cause most of the damage, because human and natural systems tolerate only a range of weather. When an event outside the range occurs, disastrous damages result. See, for example, the calculations in chapter 7 of my new book "America's Climate Problem: The Way Forward".

Posted by Robert Repetto on 06 Jan 2011

It's gratifying to hear that Nordhaus has finally opened his eyes to the reality of climate change. But to then shift to the position, "well, GDP doesn't measure economic welfare anyway", is just another form of denial. Particularly in the U.S., it is more likely to be productive to focus on the 'strategic' dimensions of climate change and climate change responses: yes, the economic damage from crop losses, infrastructure damage and extreme events; but also the risk of losing a leadership position in the technologies that will matter for future economic growth and security: clean energy technologies, energy efficiency, renewables, electric vehicles, etc.

At this point, China is taking much more proactive action in these areas that the US or my country, Australia - because they have a clear and present social and political need to do so. Low carbon energy and energy-using technologies are this Century's 'iron food bowl', and not just in China. We have pinned all our hopes on the illusion of 'clean coal' - and the poster boy demonstration project in Australia (ZeroGen) has just collapsed in a heap of debt and unfulfilled promises. Why is it so hard to recognise what's in our own best interests here? Too much ideology and not enough dispassionate analysis is clouding our vision.

Posted by Phil Harrington on 06 Jan 2011

All this is based on the desperate predictions of a failing science. Climate models are tuned to the past and have little predictability. Lindzen and Spencer have shown that feedbacks and climate sensitivity are way off the mark. There is no proof of a cause and effect between carbon dioxide and temperature. In fact, through geologic history, rising temperatures occurred before rises in carbon dioxide. Several physicists have shown that all the available infrared radiation in two narrow bands is absorbed when carbon dioxide concentrations reach 200-300 ppm. Furthermore, the bands that are absorbed only represent 8-10% of the total spectrum. "It's like a greenhouse with 90% of the glass missing".

Ice cores show that there were sharp rises and falls in temperature at the end of the last ice age. A variety of natural causes must have been responsible. Clouds and precipitation have a much larger effect on temperatues than carbon dioxide. Solar flares and the solar wind as well as ocean oscillations including the 30 year pacific decadal oscillation can affect weather patterns and cloud amounts. A 1-2% change in cloud amounts can account for all the temperature changes in the 20th century. The models contain none of these effects.

The assertion that global wamring is responsible for recent cold and snowy winters is just plain silly.

Posted by James Macdonald on 06 Jan 2011

How does one equate the value of money [which is at best an illusionary construct] with the condition of the planet we live on?

Do you clean your bedroom? Do you allow smoking in your livingroom? Do you check your stoves and heaters for gas leakage? To you make sure your garage door is open when you start your car in the morning?

Oh, no? Ok. And you wanted what kind of flowers at your funeral after a long painful disability resulting from lung desiese. - OR - The family needs the report disproving the suicide theory over the garage door incident so you can collect the insurance...DUAH!

Posted by Marina Pratt on 07 Jan 2011


Perhaps in the end the climate-change economist can help most by not presenting a cost-benefit estimate for what is inherently a fat-tailed situation with potentially unlimited downside exposure,” -Harvard economist Martin Weitzman

That's the best line in an otherwise strangely framed article. One need not accept and be blind to the assumptions and framing of the worldview of the economist, espeically as they are attempting to describe the physical and ecological world. Perhaps a more scientific framing would be better.

None of these models in any way address the realities of the situation and take place in some bizzaro world where we can move all our corn growing to another state at minimal cost, digging up the forests of the north causing more climate degredation and/or moving corn growing to canada. Net offsets in GDP with no thought going into knock on effects or realities of soil conditions in states north of kansas. The analysis becomes inane quickly from the GDP based economists thinking.

Does anyone really think that if we had 3 or 5 hurricane Katrina events in a single year we could just build more things and that construction would result in a net zero GDP loss. The very idea of a 'non-growth' scenario is beyond the thinking of all these economists.

The fact ignored in the article here on Yale 360 and in all these economic minded articles is the spiraling decline into death suggested as acceptable. We'll just take all the resources we need to build a green clean economy necessary to mitigate and reduce the incidince of future catastrophic weather and climate events and put them into rebuilding from all the damage caused by those events?

We need to utilize our resources to build smartly and change our energy generation, farming practices, land management, and wealth distribution issues to alleviate extreme poverty linked to massive population growth.

It is unrealistic to think we can use limited resources in an unlimited way to deal with ever escalating environmental damage and economic disruption. The economist is out of luck here, we need an insurance underwriter and long range thinking about the direction of our economies to begin to even tackle these issues.

$1 isn't a $1 isn't a $1 in this world. Not all money is spent equally. It might make more money to manufacutre bullets, sell bullets, shoot people with bullets, and pay for medical care and doctors and sometimes funeral expenses...that is a great increase in GDP, easily enough to offset the lost GDP from dead folks who are being replaced by births anyhow. This is insane thinking and has no place at all in the debate about how to respond and what level of action to take to mitigate and adapt to AGW.



Posted by spiritkas on 07 Jan 2011

This article misses the point, which is that no one really knows what will happen in the business-as-usual scenario, and hence no one really knows how much taking that road will cost (and this remains true even if one takes the estimates of "degrees of warming" with "CO2 concentration" as gospel). What matters is risk, i.e. the range of possible outcomes, not the "expected" case (which has zero probability of occurring). Risk is inherently harder to estimate than averages, but any intelligent trader hedges risk to the extent that this can be done without ruining profits. We could have bought insurance against climate change for a pittance three decades ago when the existence of the risk first became reasonably clear. Now that the risk has become far clearer, insuring against it will cost far more, but still nothing compared to what could happen if we pontificate until our dying breath.

Posted by ThisOldMan on 11 Jan 2011

It is logical to wish to weigh pros and cons when choosing a course of action but it is not sensible to try to do so with an inadequate analytical tool. Cost - benefit analysis is not an adequate basis for making major societal decisions because it ignores unknowns and unknown unknowns, it is inherently short-sighted, and it's use requires the assumption that there exist no deep ethical consequences of alternative options. Like a hammer, cost-benefit analysis is suitable for a limited range of tasks; it is not suitable as a basis for making decisions about all things.

Cost-benefit analysis will always underestimate the consequences of environmental damage because unanticipated damages will not be included in the analysis and because "long-term" is a meaningless concept where discounting is involved.

If a cost benefit analysis is sufficient for determining how much to alter the atmosphere of the only place in the universe known to support life, then surely it is also sufficient for determining the best policies for simpler, less weighty issues, such as in what instances abortion should be legal, whether those in a country illegally should be granted amnesty, or whether I should be allowed to own an automatic weapon. Oh, sorry, these are ethical issues.

Consider the even simpler case of how I should have spent my day. I spent most of it at my kids soccer games and ended the day with a text message from a 17-year-old who called me the best dad. (No kidding - his perception will presumably improve with time.) If I had planned my day on the basis of a cost-benefit analysis I would have had to ignore my kids and work for money all day, and certainly wouldn't have time to type this note. It seems that my less quantitative but also less blinkered basis for choosing how to spend my time was superior after all.

Posted by Peter Schulze on 16 Jan 2011

There is no example in the geological record for a rise in mean global temperatures by 2 or 4 degrees on a decadal or century time scale, as is projected with current climate change.

A rise of this magnitude within such a short time scale can only be compared to events in the geological past where mass extinctions enused from global volcanic eruptions, asteroid impacts and large scale methane release.

Andrew Glikson
Earth and paleo-climate science
Australian National University

Posted by Andrew Glikson on 11 Jan 2012

Comments have been closed on this feature.
John Carey is a freelance writer covering the environment, energy, science, technology and medicine. Until this year, he was senior correspondent at BusinessWeek, where during 21 years he wrote about a range of issues, from sequencing the human genome and global warming to tobacco regulation, election technology, cholesterol-lowering drugs and renewable energy. He is a former editor of The Scientist, and spent six years at Newsweek, where he covered science, technology, and health.



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