A sense of apocalypse hangs low over Elizabeth Kolbert’s Field Notes From a Catastrophe and Tim Flannery’s The Weather Makers, two important new books on global warming. Flannery, the director of the South Australian Museum in Adelaide and an accomplished science writer, warns: “If humans pursue a business-as-usual course for the first half of this century, I believe the collapse of civilization due to climate change becomes inevitable.” Kolbert, a writer at The New Yorker (where I also work), quotes a despairing New York University professor of physics, Marty Hoffert: “We’re going to just burn everything up; we’re going to heat the atmosphere to the temperature it was in the Cretaceous, when there were crocodiles at the poles. And then everything will collapse.”

But in many ways, the most striking thing that emerges from reading these two books and indeed from contemplating the larger phenomenon of global warming is that the earth has often been warmer than it’s likely to become in the next century–and not just for brief periods of time but for long swatches of its history. The question therefore becomes less one of apocalyptic endings–the biological world will no doubt survive global warming in some perhaps significantly altered form–than a political one of trying to parse just what kinds of changes we’ll have to make to adjust to what promises to be a brave new world.

Flannery and Kolbert are clear on the fundamentals. Greenhouse gases including not just carbon dioxide but also methane and water vapor have always existed in the earth’s atmosphere in a delicate balance with climate. By allowing solar radiation to reach the earth’s surface but trapping some of it before it radiates back out again, these gases have played a significant role in stabilizing the climate within the temperature bands that have allowed human life to flourish and expand over the past 10,000 years. Flannery points out that this 10,000-year period has been one of unusual climate stability and that it essentially includes the entire history of human civilization. He refers to it as “the long summer” and argues that climate stability may have been an essential factor in allowing humans to develop as they have.

But since the industrial revolution, we have been pumping increasing amounts of carbon dioxide into the atmosphere. By the mid-twenty-first century the atmosphere is expected to contain close to twice the carbon dioxide it did in the pre-industrial eighteenth century. This buildup of carbon dioxide has caused a rapidly accelerating warming of the earth’s atmosphere. As Kolbert notes, “1990 was the warmest year on record until 1991, which was equally hot. Almost every subsequent year has been warmer still…1998 ranks as the hottest year since the instrumental temperature record began.” The early years of this millennium were the second, third and fourth hottest until the figures came in for 2005, which established yet another record. “The world is now warmer,” Kolbert observes, “than it has been at any point in the last two millennia, and, if current trends continue, by the end of the century it will likely be hotter than at any point in the last two million years.”

The relationship between carbon dioxide buildup and the accelerating rise in the earth’s temperature is well established. It can seem almost binary–and therefore both predictable and controllable. It’s the kind of thing Americans have traditionally been good at: figure out the point at which the temperature rise becomes a problem, invent new technology, cut the levels of carbon emissions accordingly and presto, no more problem! But what renders the equation far more volatile are what Kolbert and Flannery refer to as “feedback loops,” a generic term for the many ways in which the simple carbon dioxide buildup tends to feed on itself within the larger, almost impossibly complex, climate system. These feedback loops include the fact that the Arctic ice sheet is melting and that the open water thus exposed absorbs more heat than the ice-covered ocean. The more the Arctic Ocean is exposed, therefore, the faster the heat rises. The resulting rise in Arctic temperatures has already begun to melt the Arctic permafrost, which is then likely to release enormously more carbon–frozen in place since the last ice age. An increasingly warmed atmosphere holds more water vapor (another greenhouse gas), and thus the cycle is further accelerated. As part of the general warming, the ocean too will warm, which will result in alterations to prevailing currents that are expected to cause regional droughts. One such drought is predicted for the Amazon, where, in some climate models, rainfall will decline by more than 60 percent, the temperature will rise ten degrees centigrade and the world’s largest rain forest will be transformed into an arid savannah. This in turn will release the carbon suspended in the forest into the atmosphere, further accelerating what seems like a distressingly unstoppable cycle. In other words, even if the relationship between atmospheric carbon dioxide and temperature is well established, the ways in which it plays out over the entire climate system are not. Kolbert notes that much of the interaction between the almost infinite variables involved in climate prediction can only usefully be examined in computer models of such complexity that running a single climate simulation can occupy a supercomputer for a month. The knowledge that derives from such modeling is necessarily esoteric, and it has left the scientists who run these computer studies tremendously concerned. A Princeton engineering professor, Robert Socolow, tells Kolbert that “in most of the cases, it’s the lay community that is more exercised, more anxious…. But, in the climate case, the experts–the people who work with the climate models every day…they are more concerned. They’re going out of their way to say, ‘Wake up!’ ”

What specifically worries global-warming specialists is that because the overall process is so inadequately understood, the effects of the change already set in motion may become irreversible before we’re even aware of it. The earth could soon reach a tipping point at which we might inadvertently bust our ways out of our 10,000-year cocoon of climate stability and into something else altogether. A scientist with whom Kolbert speaks likens the process to that of rocking a large boulder on the side of a hill: “So you start rocking it…and finally it starts moving. And then you realize, Maybe this wasn’t the best idea. That’s what we’re doing as a society. This climate, if it starts rolling, we don’t really know where it will stop.”

There is ample evidence that such tipping points have occurred in the past. Flannery notes that Greenland ice cores contain a record from 8,200 years ago of a period in which the temperature suddenly dropped five degrees centigrade and stayed that way for the next 200 years. This was, Flannery and Kolbert speculate, the result of a temporary collapse of the Gulf Stream–an ocean current that channels tropical waters to the North Atlantic and keeps the Northern Hemisphere warm. The flow of the Gulf Stream is intimately connected with the behavior of the Arctic ice caps, and evidence shows that the Gulf Stream has collapsed in the past. Researchers in England have already detected a weakening of Gulf Stream currents that may or may not be connected to the recent increased melting of Arctic ice.

Lest even raising this prospect seems alarmist, let it be known that the Pentagon, according to Flannery, has already made a Gulf Stream-collapse study of its own. Not surprisingly, the study, published in 2003, found national security implications. In addition to the Northern Hemisphere turning sharply colder, the Pentagon anticipated such a collapse leaving large swatches of the tropics much warmer. The study fears this could require the United States to seal its borders against a flood of desperate immigrants. Mere predictions? Maybe, maybe not. Part of the fascination of the debate over global warming is the contrast between the direness of such predictions and the underlying incompleteness of knowledge. This is not a point that either Kolbert or Flannery emphasize (although neither do they hide it). Because of the urgency of the situation and the well-known intransigence of the White House, industry groups and their political affiliates (Senator James Inhofe of Oklahoma famously referred to global warming as “the greatest hoax ever perpetrated on the American people”), both authors tend to make the case for global warming–to emphasize what’s known at the expense of what’s not. This is entirely understandable–virtually everything that’s known about global warming is alarming, and each new incremental bit of knowledge seems to make it more so–but it raises an interesting question that is perhaps close to the heart of why Kolbert and Flannery seem to fear that the global warming phenomenon may, ultimately, be an impossible one for us to cope with.

Kolbert quotes a 2005 statement by James Connaughton, head of the White House Council on Environmental Quality, as saying of global warming that “we are still working on the issue of causation, the extent to which humans are a factor.” This, in turn, is a polite variation on Inhofe’s argument when he refers to global warming as “an article of religious faith” for “alarmists.” You can dismiss such statements as classic Bush Administration disingenuousness, or you can admit that they have a root connection to legitimate epistemological questions surrounding the implications of climate change. Flannery quotes Jack Hollander, emeritus professor of Energy and Resources at the University of California, Berkeley, who is skeptical about the accuracy of climate modeling systems, which he thinks “do not provide an adequate basis for the catastrophic generalizations about future climate.” Even Robert Socolow, referring to the changes he feels will be necessary to stabilize the warming climate, tells Kolbert that “the earth is a twitchy system. It’s clear from the record that it does things that we don’t fully understand. And we’re not going to understand them in the time period we have to make these decisions.”

The important thing is to admit that the incompleteness of knowledge, the very difficulty in describing the complex relationship between cause and effect, is a factor in the global-warming debate. Flannery observes that climate change has “deep political and industrial implications” that arise from “the core processes of our civilization’s success.” The truth is that in order to address it, people are going to have to make radical adjustments not just in the ways they live but also in the ways they understand their roles in the world. This will cut a lot deeper than just trading in the Hummer for a hybrid. Ultimately, the process of accommodating to global warming is likely to demand the transformation of our dispersed suburban existences, our automobile and international-trade-based shopping malls, our coal-based electrical generation, our petroleum-based agriculture and food-distribution systems. What’s interesting is that at least some of the scientists Kolbert and Flannery interviewed think that technologically such transformations are within reach. Socolow tells Kolbert that a carbon tax that might add $15 to the average American utility bill would create a sufficient incentive to begin to turn people away from at least carbon-based electricity–the single greatest generator of atmospheric carbon dioxide. Marty Hoffert, the New York University physicist, argues that a $10 billion or $20 billion budget for primary research into new energy sources would be enough to at least jump-start a serious alternative-energy research program. But Hoffert also marvels at the peculiar logic that makes such an expenditure a political impossibility while the Bush Administration’s Star Wars missile defense system is entirely acceptable, even though it has already cost the public close to $100 billion and has yet to produce a workable system.

The problem is that the very complexity of the cause-and-effect relationship is a major factor in global warming politics. In the prevailing profoundly anti-science, anti-intellectual climate in this country, will Americans–who produce a quarter of the world’s greenhouse gases–be able to follow the complex chain of causality to connect global-warming-induced changes to their patterns of consumption? The melting of the polar ice caps may be something that the voting public can easily associate with global warming. So will the disappearance of polar bears from the wild and the disappearance of glaciers from Glacier National Park, but will voters who have been bombarded with cynicism toward “liberal elites” be willing to listen to the country’s scientists and make radical changes based on an increased frequency of Category 5 hurricanes, or persistent and ever-more severe droughts in the Amazon, the African Sahel or even the American West? The alternative, which in some ways seems more likely, is that these phenomena, which are certain to increase in a complex relationship to global warming, will result in a new isolationism, more demagoguery and perhaps more millennial religious thinking–as new and better reasons to despair of the rest of the world, close our borders and retreat into gated communities. You can’t sign off on global warming, however, without returning to the central question: If the world has frequently been as warm or warmer than it is likely to be in the near future, why is the increased warmth such a problem? Tim Flannery points to the several-thousand-year period at the end of the last ice age when the world’s temperature rose by five degrees centigrade. This was the fastest recorded rise, he notes, in recent earth history. It also happens that five degrees centigrade is the same degree of temperature rise that many climatologists expect the earth to have experienced between the beginning of the industrial revolution–the late eighteenth century–and perhaps the middle of this century. The difference, of course, is that our five-degree rise is happening–as Flannery points out–thirty times faster than the one at the close of the last ice age.

There are many problems that will result from this extreme rise in the earth’s temperature, but high among them is the difficulty that many of the earth’s living things will have in adjusting. Flannery points out, for example, that 14,000 years ago, toward the end of the last ice age, the types of forests that now grow around Montreal grew in Florida. The geologically rapid change in temperature that led to an ecological migration from Miami to Montreal nevertheless took place over several thousand subsequent years. At that point, such migrations were biologically possible. Flannery points out that “trees, birds, insects–indeed entire biotas–would migrate the length of continents as they tracked conditions suitable for them.”

But in today’s world and on the greatly accelerated time scale of modern global warming, is such adaptation still a possibility? In 2005 the United Nations published a “Millennium Ecosystem Assessment,” a study that noted that as the human population topped 6 billion, the demands it was placing on the natural world had degraded, isolated or eliminated many ecological systems. Human actions, it observed, were “fundamentally, and to a significant extent irreversibly, changing the diversity of life on Earth.” The study notes the key role that biological diversity plays in allowing ecological systems to adapt and concludes that most of the human-induced changes “represent a loss of biodiversity.”

Flannery observes that much biodiversity on today’s earth is concentrated in national parks. Many of these parks, however, are surrounded by what he refers to as “human-modified landscapes”–agricultural fields, monoculture forests, superhighways, industrial, suburban and urban sprawl, malls–that will act as barriers to the types of ecosystem migrations that took place during earlier periods of temperature rise. Will these parks turn into biological traps? Will whole ecological systems, locked into island parks, be doomed to extinction? Both Kolbert and Flannery cite a recent British study, published in Nature, which surveyed 1,103 species of plants and animals drawn from regions covering 20 percent of the globe and looked at how they’d fare by the end of this century under different temperature-rise scenarios. Depending on the scenario, the study anticipated rates of extinction of 20 to 33 percent–at least one in five species. For species that are locked into place and at the high end of predicted temperature rise, the study projects a much higher extinction rate–58 percent.

Should we be concerned about this? We should be if only for one good reason. Chris Thomas of the University of York, the principal author of the extinction study, points out that crops are biological species, as are diseases. If there’s overwhelming evidence that species are changing their distribution, he explains to Kolbert, “we’re going to have to expect exactly the same for crops and pests and diseases.” In other words, areas that are already likely to be afflicted by temperature rise and drought may soon also be afflicted by regionally new diseases and regionally new agricultural pests–afflictions to which they will have little or no immunity. Flannery anticipates a tripling of the percent of the world’s population at risk for food shortage. Kolbert notes that shifts in monsoon patterns and ocean currents could produce streams of refugees numbering in the millions.

Even reading about such propects can seem overwhelming. The gravity of the subject clearly gets to Flannery, who, in a coda to his book, suggests the creation of a corps of international United Nations-like green-helmeted carbon police. This is a non-starter if there ever was one. Kolbert, by contrast, expresses her opinions through the many scientists she’s interviewed and seems to have arrived at a deep fatalism. She quotes Marty Hoffert: “I’m not sure we can solve the problem. I hope we can. I think we have a shot. I mean, it may be that we’re not going to solve global warming, the earth is going to become an ecological disaster, and, you know, somebody will visit in a few hundred million years and find there were some intelligent beings who lived here for a while, but they just couldn’t handle the transition from being hunter-gatherers to high technology.”