#196: Coal and Climate

MuseLetter #196 / August 2008
by Richard Heinberg

[This month’s essay is another chapter from the retitled book-in-progress, BLACKOUT: Coal, Climate and the Last Energy Crisis.]

Recent reports on global coal reserves, surveyed in previous chapters, generally point to the likelihood of supply limits appearing relatively soon—within the next two decades (a contrary view is represented solely by the BGR report [“Lignite and Hard Coal: Energy Suppliers for World Needs until the Year 2100 – An Outlook,” 2007]). According to this near-consensus, coal output in China, the world’s foremost producer, could begin to decline within just a few years.

Since coal is the most significant source of human-generated greenhouse gas emissions, releasing about twice as much carbon dioxide per unit of energy produced as natural gas, the news that there may be much less coal available to be burned than commonly thought should be heartening to climate scientists and environmental activists, and to policy makers and citizens concerned about the fate of the planet. Reduced estimates of future coal supplies should be factored into climate models—which typically assume that there is enough coal available to permit continued expansion of usage well into the next century.

At the same time, because global warming has emerged as the central environmental issue of our era, climate concerns will inevitably impact how much coal we continue to burn and how we burn it—whether these concerns come to be expressed through caps on emissions, carbon taxes, cancellation of orders for new coal-fired power plants, or the promotion of new carbon sequestration technologies. In any case, the coal industry will be—indeed, already is being—forced to change.

These two trends are surely destined to interact, and the uncertain result will shape climate and energy policy in the years to come.

A Tale of Two Crises

The idea that carbon dioxide emissions from burning fossil fuels might contribute to a greenhouse effect raising global temperatures was initially floated in the 1950s. The first evidence that global atmospheric carbon dioxide (CO2) levels and global temperatures were both indeed increasing appeared in the early 1960s. The 1980s saw the first calls for international action to limit carbon emissions, with the first Congressional hearings held in 1988, the same year Margaret Thatcher delivered a Climate Change speech to the Royal Society. The UN’s International Panel on Climate Change (IPCC) released its initial report in 1990. In 1992, the Earth Summit in Rio de Janeiro produced the UN Framework Convention on Climate Change. The third IPCC report, issued in 2001, stated that global warming, unprecedented since the end of last Ice Age, is “very likely,” with severe surprises possible. By this time, debate among scientists over the question of whether human activities were contributing substantially to Climate Change had effectively ended. In 2003, numerous observations raised concern that the collapse of ice sheets in West Antarctica and Greenland could raise sea levels faster than most had believed possible. That same year, a deadly summer heat wave in Europe riveted public opinion on the issue. Work to retard emissions accelerated in Japan and Western Europe, and among US regional governments and corporations. In 2007 the fourth IPCC report warned that serious effects of warming have already become evident, and that the cost of reducing emissions would be far less than that of the damage they will cause. In the same year, the north polar ice cap melted to such an extent that the northwest shipping passage was opened for the first time in history.

In short, over the past 50 years anthropogenic Climate Change has evolved from a mere hypothesis to a robustly documented and widely researched phenomenon; and from a concern on the part of just a few climate scientists to a center-stage issue dominating not just environmental studies, but economic planning and global politics as well.

Yet while Climate Change is the greatest environmental crisis that humanity has ever faced, it is not the only serious challenge confronting us. Climate Change is a “sink” problem—the result of dumping into the environment a waste product from the burning of fossil fuels. But there is a simultaneous “source” problem arising from the gradual depletion of the fuels we are burning.

At about the same time the greenhouse hypothesis was first being proposed, geophysicist M. King Hubbert was publishing his first study on the phenomenon of oil depletion. Previously, supply concerns about fossil fuels had centered on the question of when they would run out, and by most estimates that would not happen for a very long time. Hubbert reframed the discussion by pointing out that the rate of extraction of fossil fuels within any given region, or the world as a whole, will reach a maximum and begin to decline long before the resource is exhausted; further, he suggested that it is this peaking of production that is critical for economic planning. By the mid-1970s, US oil production had peaked and begun to decline, as Hubbert had estimated that it would. By this time, Hubbert and a few other petroleum geologists were forecasting a peak in global oil production around the turn of the century. In 1998, Colin Campbell and Jean Laherrère published a landmark article in Scientific American titled “The End of Cheap Oil,” in which they argued that oil reserves in the Middle East were overstated, and that world petroleum production would hit its maximum before 2010. At the time, the world oil price was hovering in the range of $12 per barrel. By 2000, British oil production from the North Sea had begun to fall, and it was apparent that about half the world’s other oil producing nations were also in plateau or decline. In 2005, a study for the US Department of Energy concluded that the world oil production peak would have “unprecedented” social, economic, and political consequences. In 2008, the International Energy Agency warned of a severe mismatch between world petroleum supply and demand in the years immediately ahead. By this time oil’s price had risen to nearly $150 a barrel, and soaring fuel costs were severely impacting the automobile industry, the airline industry, the trucking industry, and tourism.

Because natural gas and coal are also non-renewable, it is inevitable that depletion will result in peaks and declines of output for these fuels as well. However, studies—even unofficial ones—of Peak Gas and Peak Coal have lagged behind those of Peak Oil. While some awareness of coal limits can be traced back at least to the work of Andrew Crichton in 1948, the discussion of Peak Coal really started with the appearance of reports from Energy Watch Group and the National Academy of Sciences, both in 2007. A report from Energy Watch Group on global natural gas supplies is due later this year.

Meanwhile, though the timing of the global oil, gas, and coal production peaks is still controversial, the peaking concept has become sufficiently accepted that its significance for Climate Change has begun to be explored.

Climate Models and Fossil Fuel Supplies

Models for future impacts of Climate Change must be based on two essential parameters: the quantity of future greenhouse gas emissions that can reasonably be anticipated; and the sensitivity of climate to added increments of atmospheric greenhouse gases. Both of these parameters are subject to ongoing research and revision.

In its Special Reports on Emissions Scenarios (SRES), the International Panel on Climate Change (IPCC) has published a series of 40 scenarios for the fossil fuel contribution to future Climate Change. The latest of these reports, in 2007, was a multi-year effort involving more than 1,000 authors and more than 1,000 reviewers. In the assessment modeling, limitations in fossil fuel supplies are not considered critically. For example, in 17 of the scenarios, world oil production is higher in 2100 than it was in 2000—a situation not considered likely even by OPEC.

In 1996 the European Environment Council had said that the global average surface temperature increase should be held to a maximum of 2 degrees C above pre-industrial levels, and that to accomplish this the atmospheric concentration of CO2 will have to be stabilized at 550 parts per million (the pre-industrial level was 280 ppm and current concentration is close to 390 ppm, though the addition of other greenhouse gases raises the figure to the equivalent of 440 to 450 ppm of CO2). The European Union has more recently adopted a target of 450 ppm of CO2, in line with recommendations from climate scientists.

However, the IPCC scenarios suggest that if fossil fuel consumption continues to increase throughout the century, CO2 concentrations could reach a staggering 960 ppm by 2100, which would result in six or more degrees of warming, tilting the global climate into an entirely new regime and triggering an endless list of environmental horrors.
Jean Laherrère was an early critic of the SRES, arguing in 2001 that failure to understand realistic limits to fossil fuel supplies and to incorporate these into climate models was resulting in highly unrealistic estimates of future atmospheric CO2 concentrations, future temperature increases, and future effects on climate, ocean levels, and so on. (“Estimates of Oil Reserves”)

In April 2007, James E. Hansen, head of the NASA Goddard Institute for Space Studies in New York City, who has arguably done more than any other scientist in recent years to both assess and publicize the likely impacts of Climate Change, co-authored an important paper (together with P. A. Kharecha of the Columbia University Earth Institute) that discusses fossil fuel supply limits. These authors explicitly mention Peak Oil, and stress that, “[I]t is important to estimate expected atmospheric CO2 levels for realistic estimates of fossil fuel reserves and to determine how the CO2 level depends upon possible constraints on coal use.”

In this paper, (“Implications of ‘Peak Oil’ for Atmospheric CO2 and Climate,”), Kharecha and Hansen discuss five scenarios. In their Business as Usual base case, “Peak oil emission . . . occurs in 2016 ± 2 yr, peak gas in 2026 ± 2 yr, and peak coal in 2077 ± 2 yr.” Most of the IPCC scenarios show far higher CO2 concentrations than Kharecha and Hansen’s Business As Usual (BAU) scenario.

The authors also discuss a “Coal Phase-out” scenario that “moves peak coal up to 2022.” This second scenario “is meant to approximate a situation in which developed countries freeze their CO2 emissions from coal by 2012 and a decade later developing countries similarly halt increases in coal emissions.” This Coal Phase-out scenario shows a peak of atmospheric CO2 concentrations at about 445 ppm in 2046.

One message from the paper is that climate mitigation efforts should not focus so much on reducing oil and gas demand, as these fuels are supply-limited. Rather, they should concentrate on reducing the exploitation of coal and unconventional fossil fuels, since these are demand rather than supply limited for the time being. This message is more explicit in Hansen’s June 23, 2008 Congressional testimony:

Phase out of coal use except where the carbon is captured and stored below ground is the primary requirement for solving global warming. Oil is used in vehicles where it is impractical to capture the carbon. But oil is running out. To preserve our planet we must also ensure that the next mobile energy source is not obtained by squeezing oil from coal. Global Warming Twenty Years Later: Tipping Points Near

However, it appears that Kharecha and Hansen did not take fully into account the recent coal supply reports surveyed in this book (though they do mention the NRC report of 2007). The authors write, “[E]ven if coal reserves are much lower than historically assumed . . . there is surely enough coal to take the world past 450 ppm CO2 without mitigation efforts such as those described here,” but they do not define what they mean by “much lower.” In fact, the EWG, Höök et al., Laherrère, and Rutledge forecasts cited in this book all show future coal supply limits that are roughly in accord with Kharecha and Hansen’s Coal Phase-out scenario, and that achieve a target of approximately 450 ppm CO2.

A month after the release of the Kharecha and Hansen paper, Kjell Aleklett, professor of Physics at Uppsala University and President of Association for the Study of Peak Oil (ASPO), published an article provocatively titled, “Global Warming Exaggerated, Insufficient Oil, Natural Gas and Coal” (May 18, 2007). Aleklett’s main purpose was to take the IPCC to task:

The sum of all fossil resources that the industry considers available is presented annually in BP Statistical Review. According to this rather optimistic estimate, the total energy of all oil, natural gas and coal amounts to 36 Zeta joules (ZJ), a gigantic amount of energy. This is more than what our research group considers likely, but it is still less than what do the [SRES] scenario families A1, A2, B1 and B2 require. . . . Up to 2100, IPCC prognosticates that A2 will need between 70 and 90 ZJ, that is, twice as much as the industry believes is available. . . . We need a new assessment of future temperature increases based on a realistic consumption of oil, natural gas and coal.

David Rutledge published his paper, “The Coal Question and Climate Change,” cited throughout this book, in June 2007. In it, he compared the results of Hubbert linearization modeling of future coal production with the IPCC models. He concluded, “Our Producer-Limited Profile has future fossil-fuel production that is lower than all 40 of the IPCC scenarios, so it seems that producer limitations could provide useful constraints in climate modeling.” More specifically, “The Producer-Limited Profile gives a peak of 460 ppm in 2070″—which is only marginally above the widely accepted target of 450 ppm. The implication is clear: sufficient greenhouse gas reductions will be accomplished by fossil fuel depletion alone, without any need for carbon emissions regulatory policy.

In short, the implication of the latest research might appear to be that Peak Oil, Peak Gas, and Peak Coal will together solve the problem of global Climate Change, without need for intervention by policy makers.

However, this could be a dangerously premature conclusion.

Climate Sensitivity

Recall that climate models depend not only on future carbon emissions (which are contingent, as we have just seen, on fossil fuel supplies as well as on energy policy) but also on climate sensitivity. How will the global climate respond to a given additional increment of carbon dioxide? In general, as observations of impacts from Climate Change are being logged, they are tending to show that past assumptions about climate sensitivity have, if anything, been too timid and conservative.

Most climate sensitivity models are now being seen as subject to three problems. First, they tend to assume a linear relationship between atmospheric greenhouse gas concentrations and global temperature increase, whereas there is mounting evidence that the relationship is actually non-linear. Second, they tend to assume a linear relationship between global temperature increase and actual impacts to ecosystems and human society, whereas there is mounting evidence that this relationship is also non-linear. Third, such models have created a questionable basis for policy: it has been widely accepted that a future temperature increase of two degrees C (which is assumed to be tied to a greenhouse gas concentration of 450 ppm) must be our target limit, above which changes to the climate will be catastrophic, irreversible, and unacceptable—whereas, in fact, we may already be seeing degrees of change that are catastrophic, effectively irreversible, and unacceptable.

Non-linearity in the relationship between greenhouse gases and temperature increase was demonstrated by a 2005 study by researchers at the Potsdam Institute for Climate Impact in Germany, which concluded that—to keep the temperature from increasing more than two degrees C—the atmospheric concentration of CO2 would need to be stabilized at then-current levels (i.e., 380 ppm). Among other things, the study pointed out that the biosphere’s ability to absorb carbon is being reduced by human activity, and this must be factored into the equations; by 2030, this carbon-absorbing ability will have been reduced from the current four billion tons per year to 2.7 billion tons.

Non-linearity of the consequences of global warming is illustrated by several self-reinforcing feedback mechanisms that, if triggered, could result in effects spiraling far out of human control. Perhaps the scariest of these has to do with the vast amounts of methane (a greenhouse gas over 20 times more potent than carbon dioxide) locked in the ocean floor and in the frozen soils of Siberia, Northern Europe, and North America. Climate warming could trigger a rapid thawing that would release billions of tons of this stored methane into the atmosphere. More methane in the atmosphere would create more warming, which would release still more methane. The ultimate consequence might be the tipping of the planet into a new climate regime so different from the current one that many higher life forms (including humans) might find survival difficult or impossible.

The inadequacy of policies that use 450 ppm and a two degree average global temperature increase as targets or limits is illustrated by evidence that catastrophic Climate Change has already been set in motion on the basis of a mere one degree C global temperature rise. For example: Recent observations have established that oceans are absorbing increasing amounts of carbon dioxide from the atmosphere, resulting in their gradual acidification. In the last two centuries, the oceans have absorbed roughly half of the amount of CO2 emitted by fossil fuel use and cement production. This has caused ocean pH to fall. Ocean acidity will be devastating to the marine environment within a short period of time—tens of years instead of hundreds of years. Seawater undersaturated in calcium carbonate will make it difficult for shelled organisms to create skeletons and shells. These organisms form an essential link in the aquatic food chain; thus all life in the seas will be impacted. Given that the oceans have already absorbed a substantial amount of carbon dioxide, we are already committed to an irreversible amount of ocean acidification. It is likely that rebalancing the ocean pH will take thousands, or even hundreds of thousands, of years.

Ocean acidification again illustrates the disturbing fact that very little about “global warming” is simple or linear. Instead, the consequences of greenhouse gas emissions are complex, mutually interacting, and far-reaching. Rather than merely having to accustom ourselves to winters and summers a degree or two hotter, we will see far more severe storms of all kinds, as well as rising sea levels, collapsing ecosystems, disease outbreaks, species extinctions, profound challenges to agricultural production, and more. We may already have committed ourselves to centuries of overwhelming environmental damage.

If we are already seeing fundamental changes to the world’s oceanic food chain, to the Arctic sea ice, and to glaciers that feed some of the world’s most important river systems, can we afford to commit ourselves to still higher atmospheric greenhouse concentrations (450 ppm instead of the current 390), and to a two degree temperature increase above pre-industrial levels instead of the single degree that has already produced these impacts?

In a recent paper, “Target Atmospheric CO2: Where Should Humanity Aim?“, James Hansen, along with eight co-authors, questioned the 450 ppm target and suggested a new one:

Our current analysis suggests that humanity must aim for an even lower level of GHGs. Paleoclimate data and ongoing global changes indicate that ‘slow’ climate feedback processes not included in most climate models, such as ice sheet disintegration, vegetation migration, and GHG release from soils, tundra or ocean sediments, may begin to come into play on time scales as short as centuries or less. Rapid on-going climate changes and realization that Earth is out of energy balance, implying that more warming is ‘in the pipeline,’ add urgency to investigation of the dangerous level of GHGs. . . . We use paleoclimate data to show that long-term climate has high sensitivity to climate forcings and that the present global mean CO2, 385 ppm, is already in the dangerous zone. . . . Ongoing Arctic and ice sheet changes, examples of rapid paleoclimate change, and other criteria cited above all drive us to consider scenarios that bring CO2 more rapidly back to 350 ppm or less.

On the basis of this article and the recent findings that prompted it, climate activists such as Bill McKibben and George Monbiot have also begun to call for more stringent targets—350 ppm target for atmospheric CO2 concentrations and a 100 percent reduction in carbon emissions by 2050.

This is a far more rapid and drastic reduction in carbon emissions than can be achieved by fossil fuel resource depletion alone.

Further, relying on fossil fuel depletion to safeguard the world’s climate would entail a serious risk: What if the new lower estimates of coal reserves turn out to be wrong? Clearly, the world’s oil and coal reserves are a mere fraction of total resources. If somehow a way were found to transform a significant portion of remaining resources into reserves, this could entail a significant increase in atmospheric carbon emissions.

This risk also extends to unconventional fossil fuels such as tar sands, shale oil, and methane hydrates. While the potential for the development of these resources is often overstated, since current technology will permit only a very slow extraction rate for tar sands and perhaps no commercial extraction at all of oil shale and methane hydrates, nevertheless there is always the possibility that new technologies will enable their exploitation on a wide scale. Without a stringent emissions policy in place, the consequences for the global climate would be profound.

In general, human society faces a conundrum: unless non-fossil sources of energy are developed quickly, or unless society finds a way to operate with much less energy, and preferably both, the depletion of higher-quality fuels (natural gas and oil) will mean that efforts to obtain more energy will entail burning ever dirtier fuels, and doing so in proportionally larger quantities in order to derive equivalent amounts of energy.

Therefore, to the question, “Will coal, oil, and gas depletion solve Climate Change?”, the answer is an unequivocal no.

Will Climate Change Solve Peak Coal?

If some Peak Oil-Coal-Gas analysts suggest that depletion will stop Climate Change, climate activists look at the matter the other way around. While peaks and declines in the production of fossil fuels will undoubtedly have enormous societal consequences, these nevertheless pale compared to the potential ecological effects of Climate Change. Peak Oil may result in the collapse of the global economy; Climate Change could do so as well, while also devastating Earth’s ecosystems in a way that would require millennia, perhaps millions of years, for planetary recovery.

But if we proactively deal with Climate Change by reducing fossil fuel consumption, the result will obviously be a reduction in dependence on fossil fuels—and therefore a solution to the problems of Peak Oil, Gas, and Coal. Therefore all that is needed is a clear, sustained, vigorous policy focus on reducing greenhouse gas emissions.

There is some evidence to support this argument. Efforts to reduce carbon emissions are already having an impact on the coal industry, primarily in the US and Europe (though not nearly to the same degree in China and India). In the US, nearly 90 percent of all new coal power plant projects proposed between 2000 and 2006 were delayed or cancelled, according to an October 2007 report by the US Department of Energy—many over concerns about future carbon emissions regulations. Of 151 proposals for new plants submitted in early 2007, almost half had been dropped by year’s end, many blocked by state governments or delayed by court challenges. Most recently, in July 2008 a judge in Georgia threw out an air pollution permit for a new coal-fired power plant because the permit did not set limits on carbon dioxide emissions. In Europe new coal plants are faring better only because higher-efficiency power plants are being proposed.

Climate mitigation efforts typically center on “cap and trade” (or “cap and dividend” or “cap and share”—alternative regimes being proposed by a number of economic equity activists), or on carbon taxes. Any of these policies to restrict carbon emissions will inevitably reduce fossil fuel consumption, impacting coal more than other fuels simply because of coal’s higher carbon content. While future coal-burning power plants could be constructed to capture carbon, which could then be permanently sequestered underground (a technology discussed in the next chapter), over the short term reducing carbon emissions simply means using less coal.

If these efforts were to pick up speed, they would reduce demand for coal (and other fossil fuels), thus heading off shortages and keeping prices lower.

But will climate concerns succeed in driving policy in the face of energy scarcity? Currently, global coal consumption is still growing—faster by volume, indeed, than the consumption of any other energy resource. Can nations experiencing shortages of oil and battered by high energy prices be persuaded to forgo the still relatively cheap energy from coal in order to avert environmental consequences for future generations?

From the perspective of climate scientists and activists, there can be no question: whatever short-term economic pain society may experience as a result of deliberately reducing fossil fuel consumption can hardly be compared with the overwhelming catastrophe that unbridled Climate Change would bring. However, policy makers may look at the evidence through an entirely different lens—one that discounts the future in favor of the present.

In financial markets, the discount rate is the rate that a stock analyst might use to discount a company’s future earnings stream for the purposes of present investment. In his book Material Concerns: Pollution, Profit and Quality of Life, Professor of Sustainable Development and UK government advisor Tim Jackson describes it this way:

[F]uture costs and benefits are taken to have a lower value than present costs and benefits. We can think of the discount rate as the rate of return which is required on capital invested by the company. The higher the discount rate, the lower the value of future costs against present costs. For example, a cost of $200,000 which occurs twenty years in the future has a net present value of $44,000 at 5 percent and $10,400 at 10 percent discount rate. The further into the future costs and benefits arise, the lower their value compared with present costs and benefits.

Environmental psychologists argue that discount rates are rooted in fundamental human psychology, and perhaps even hardwired into our genes and nervous systems. We instinctively value the concrete present over the likely or hypothesized future.

The relevance for Climate Change—and other environmental issues, such as resource depletion—is clear: we tend to discount future costs (such as the impact of melting glaciers) just as we do future profits. Thus, asking society to endure present pain in order to avert more widespread suffering in the future is problematic. The present pain must be minor, and the future suffering profound and credible and not too many years distant, in order to persuade us to take an action that we will find uncomfortable or unpleasant.

In the early years of the decade, as the global economy was booming, policy makers in many nations gave considerable attention to Climate Change. Heads of state conferred, strategies were debated, and agreements were forged. Today, as energy scarcity cripples national economies with pain that is both palpable and growing, there is likely to be a greater tendency to discount the future costs of Climate Change in favor of satisfying immediate demand for fuel, no matter how carbon-intensive it may be. There is abundant evidence that this is indeed occurring.

In Europe, while top climate experts offer ever-shriller warnings about the effects of carbon emissions, Italy is planning to increase its reliance on coal from 14 percent of total energy to 33 percent. Throughout the continent, about 50 new coal-fired power stations are being planned for the next five years. The driver for this new coal boom is unequivocally clear: higher natural gas prices. In Germany, 27 new coal plants are planned by 2020, many fueled by lignite—which can produce a ton of carbon emissions for every ton of coal burned.

In the US, despite the cancellation of so many new coal plants in recent years, the National Mining Association projects that about 54 percent of the nation’s electric power will be coal-fired by 2030, up from the current 48 percent.

Depletion defeats climate policy in other ways. Carbon taxes become a harder policy to sell as energy prices climb; coal cutbacks are more difficult to make when natural gas is getting more expensive and electricity grids are browning out; and using coal to make liquid fuels starts to look attractive as diesel prices escalate.

Will efforts to address Climate Change solve the economic problems arising from coal, oil, and gas depletion and increasing scarcity? It is possible in principle, but in reality the stronger likelihood is that energy scarcity will rivet the attention of policy makers and private citizens alike because it is an immediate and unavoidable crisis. The result: as scarcity deepens, support for climate policy may fade even as climate impacts worsen.

A Combined Approach

Clearly, the world needs energy policies that successfully address both Climate Change and fuel scarcity. Such policies are likely to be devised and implemented only if both crises are acknowledged and taken into account in a strategically sensible way.

If policy makers focus only on one of these problems, some of the strategies they are likely to promote could simply exacerbate the other crisis. For example, some actions that might help reduce the impact of Peak Oil—such as exploitation of tar sands or oil shale, or the conversion of coal to a liquid fuel—will result in an increase in carbon emissions. On the other hand, some actions aimed to help reduce carbon emissions—such as carbon sequestration or carbon taxes—will make energy more expensive, which, in a situation of energy scarcity and high prices, may be politically problematic and therefore a waste of climate activists’ and policy makers’ limited resources.

However, many policies will help with both problems—including any effort to develop renewable energy sources or to reduce energy consumption.

For strategic purposes, it is important to understand our human tendency to discount future problems. We must assess which threats will come soonest, and make sure that our sometimes frantic efforts to respond to these immediate necessities do not exacerbate problems that will show up later. Peak oil is clearly the most immediate energy and resource threat that policy makers must deal with. Peak Coal and Climate Change may seem comparatively distant. But all must be taken seriously if we are to do any better than merely to lurch from crisis to crisis, with each new one worse than the last.

If energy scarcity forces policy changes before climate fears can do so, then perhaps world leaders will find that it makes more sense to ration fuels themselves by quota, rather than the emissions they produce. In any case, it will help everyone concerned to have a clear idea of the ultimate extent of coal, oil, and natural gas reserves and future production, as well as a realistic understanding of climate sensitivity and hence the environmental and economic costs of continuing to burn fossil fuels even in depletion-constrained amounts. Otherwise, the policies pursued may simply waste precious time and investment capital while actually making matters worse.

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