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Climate: What You Need to Know

Visitors to Greenland’s ice sheet, 2008; photograph by Olaf Otto Becker

Bill McKibben’s new book is a passionate appeal from a writer who has dedicated his efforts to warning of the risks posed by human-driven climate change. It describes the challenges we face—whether from effects on the environment that are already occurring, or from those that will occur due to the greenhouse gases we have already emitted and are likely to emit in the coming decades—if we do not act to curb emissions. But while McKibben insists on the importance of strong action to reduce those risks, he struggles to find grounds for optimism and often tilts toward a pessimism that has characterized recent works by other environmentalists, such as James Lovelock.

The title, Eaarth: Making a Life on a Tough New Planet, sums up McKibben’s main theme: we have now altered the climate to such an extent that the planet as we knew it no longer exists, and it should have a new name, Eaarth. The idea that we should find a way of acknowledging the fundamental impact that humans have had on the earth is not new. Paul Crutzen, who shared the Nobel Prize for chemistry in 1995 for showing how chlorofluorocarbons, then common in aerosols, caused the hole in the ozone layer, suggested ten years ago that the current geological epoch should be called the “anthropocene” in order to “emphasize the central role of mankind in geology and ecology.”

In 2007, McKibben launched “350 .org,” a group that advocates the need to stabilize concentrations of carbon dioxide in the atmosphere at 350 parts per million, and thus stay as close as we can to the levels occurring over the last few thousand years during which we created our civilizations. That is compared with the preindustrialization concentration of about 280 parts per million. The trouble is that the current concentration is about 385 parts per million, according to the US government’s Carbon Dioxide Information Analysis Center. And when other greenhouse gases, such as methane, are taken into account, the overall level is about 435 parts per million of carbon-dioxide-equivalent. For this reason, many of the policies for controlling climate change that have been proposed so far focus on stabilization at 450 parts per million of carbon-dioxide- equivalent as being the best we can do to limit the great risks from climate change.

We are likely to exceed that level within the next decade but, with strong action, concentrations of greenhouse gases could peak in this decade and, over a long period of time with continued strong action, return to 450 parts per million or below. But if we carry on with something like “business as usual,” we may reach concentrations by the end of the century that would imply a significant chance, perhaps as high as 50 percent, of a rise in global temperature of 5˚C or more above its level in the nineteenth century. This would be a temperature that has not been seen on the planet for more than 30 million years (Homo sapiens has been here for only around 200,000 years). The map of where people could live would probably be radically redrawn. This could imply, for example, that some areas would become deserts, some would be inundated, and many subject to radical change in weather patterns or in the location and flows of rivers. This could mean in turn the movement of hundreds of millions or billions of people. History suggests that movements of people on such a scale would likely involve extended, severe, and global conflicts.

McKibben explains that his conclusion about climate change draws on a presentation by the distinguished NASA scientist James Hansen at a scientific conference in December 2007 in which he claimed that 350 parts per million should be the upper limit for atmospheric concentrations of carbon dioxide, and that we have already passed a level that could be described as “safe.” With not much immediate prospect for returning below 350, McKibben’s book is an attempt to outline how our lives must change because “the earth that we knew—the only earth that we ever knew—is gone.”

In the opening chapter, he assails the reader with an array of statistics and facts about changes that are already visible in an effort to counter what he sees as misguided attempts to portray climate change as a problem only for future generations. Most of his catalog of consequences is supported by extensive footnotes. McKibben, however, might be criticized for relying too heavily on media reports rather than scientific references. Some of his opponents will no doubt seek to undermine the book by disputing a figure here or a fact there. But his overall thesis that we are already seeing widespread effects of climate change is sound and supported by much robust scientific evidence.

A careful consideration of the scientific analysis and evidence indicates that there is indeed a very powerful case that the risks from unmanaged climate change are immense. It was in 1824 that Joseph Fourier observed that the surface of the earth was much warmer than it would be without its atmosphere. About 150 years ago, John Tyndall showed through a series of experiments that the presence of gases such as carbon dioxide was responsible for creating the greenhouse effect—the trapping of sunlight as heat by the atmosphere.

By the end of the nineteenth century, the Swedish scientist Svante Arrhenius had begun to calculate the potential magnitude of warming that would result from an increase in greenhouse gases in the atmosphere. And by the mid-twentieth century, some of the physical mechanisms behind the greenhouse effect had been understood. Essentially, the molecules of certain gases oscillate in a way that interferes with longer-wavelength radiation that arises when solar energy is reflected back from the earth’s surface, with the result that the solar heat is trapped in the atmosphere: in the 1940s, Walter Elsassar transferred into meteorology insights of quantum mechanics from the 1920s and 1930s concerning absorption.

We now know that the concentration of carbon dioxide in the atmosphere is more than a third higher than it was before we started to burn coal and other fossil fuels on a major scale with the advent of industrialization, and higher than it has been for at least 800,000 years. As a result, the global average temperature has started to rise, by about 0.7˚C in the past one hundred years. And temperatures will continue to rise for at least the next couple of decades purely in response to current levels of greenhouse gases, even if we stopped emitting them today. With this warming come changes not just in weather and temperature extremes, but, crucially, changes in levels and distributions of water: storms, floods, droughts, river flows, rises in sea level. In other words, changes in the fundamental historical determinants of how and where we live our lives.

Thus the greenhouse effect is not some airy and speculative attempt to explain some mysterious correlation. It is basic science built over nearly two hundred years. The evidence has been accumulating in the laboratory and by observation, reinforcing both the underlying theory and the understanding that the effects are major. This evidence includes ice core data, extending back 800,000 years, that allow approximate estimates of both carbon dioxide and temperature, more detailed instrumental temperature records for the past 150 years or so, and more precise recent measurements of greenhouse gas levels in the atmosphere.

This is no Kuhnian paradigm, teetering on the edge of acceptability and requiring constant ad hoc adjustments and add-ons to sustain it as more and more difficult evidence emerges. On the contrary, this is a scientific finding with a sound theoretical foundation that grows ever stronger as evidence of many different kinds accumulates. It is the various claims by skeptics that are clearly ad hoc and unable to explain the data, such as the claim that it is all a consequence of urban heat islands, or short-term fluctuations from El Niño and La Niña, and so on. None of these attempts can explain a strong underlying global trend.

At the same time, we must recognize that predictions must be in terms of risks, uncertainties, and probabilities. There is uncertainty about future emissions, about the possibilities of absorption of greenhouse gases by the land, forests, and oceans, about the magnitude of warming from changes in greenhouse gas levels, and about the effects on local climates around the world. The issue for policy is how to manage risk, taking account of strong scientific evidence that the risks are potentially very large. These are not small probabilities of something nasty, but large probabilities of something catastrophic.

To deny the urgency of strong action in the face of all the evidence is unscientific, irrational, and dangerous. It is unscientific because it dismisses sound science and evidence built over a long period. It is irrational because such denial would require more than just querying some aspects of the science. It would require great confidence both that the scientific findings are wrong and that the risks are small, since the consequences of being mistaken in assuming that the science is right or that it is wrong would be very different.

Acting as if the scientific evidence were wrong would lead us to concentrations of carbon dioxide carrying immense risks if the science were right. Acting as if the scientific findings were right might lead us to excessive investment in developing low-carbon technologies and protecting forests if the findings turned out to be wrong; but these actions are nevertheless likely to have very substantial other benefits in energy security, energy efficiency, biodiversity, and so on. Finally, denying the urgency of strong action is dangerous because the process by which emissions become concentrated has a ratchet effect, and delay in action results in higher concentrations and a more difficult “starting point.”

There is much more scientific work to do, and many uncertainties are likely to remain, but the evidence is overwhelming that the risks are large and that delay will be dangerous. The weight of this theory and evidence is no doubt why those who deny that greenhouse gases cause climate change have to resort to tactics similar to those used a few decades ago to dispute the impact of smoking on health. One such tactic is to find one or two weak or erroneous scientific papers among the many thousands of good ones and use them as an implied smear on all the rest. Another is to make use of the irrational argument that the remaining uncertainties imply that the best hypothesis is to assume that the risks are negligible. Another is to try to deliberately confuse trends and cycles. There will be cycles and random events but the underlying trend is strong. And as in the case of smoking, there are powerful vested interests ready to fund the sowing of the seeds of doubt.

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