Deep Future

by Curt Stager

  These two factors together—the inherent weakness of the next cooling cycle and the longevity of our carbon pollution—lead to one astounding conclusion. Not only have we warmed the world during this century with our carbon emissions; we’ve also stopped the next ice age in its tracks.

  According to recent computer model studies, this may be only the beginning of our influence over the coming and going of ice ages, depending on what we do during the next century or two. If we hold ourselves to a relatively moderate sum total of fossil fuel emissions before switching to alternative energy sources, then we skip the next glaciation in 50,000 AD. But more of those natural cooling pulses will develop later on. When the next big one strikes the Northern Hemisphere some time around 130,000 AD, the greenhouse pollution legacy of a moderate-emissions scenario will have faded to insignificance, leaving nothing to resist glaciation. Once again, ice will bury the northern sectors of the northern continents. Or rather, it will do so unless we burn through all of our remaining coal reserves during the next century or so. If we go down that profligate path instead, there won’t be any ice ages for a very long time: not in 50,000 AD, not in 130,000 AD, and not during the other insolation minima of the next half million years.

  How should we react to this news? When I imagine our carbon footprint kicking the door closed on an ice age, my initial reaction is one of shock mingled with a twinge of fear. But a second, rather confusing response follows when I imagine our carbon emissions saving the northern United States, Canada, and much of northern Eurasia from being crushed under gigantic ice sheets.

  It would be stretching the bounds of credibility to say that greenhouse pollution is anything but a vexing problem. But on the scale of planetary disaster, an ice age is to global warming as thermonuclear war is to a bar brawl. We’re certainly justified in worrying about the environmental disturbances that are coming our way, but even this situation is arguably better than losing entire nations and ecosystems to total icy destruction. What if we had to choose between the two options?

  In fact, we do face that very choice as we weigh our possible responses to modern climate change. Most of the more extreme negative effects of today’s fossil fuel emissions will be felt within the next millennium or so, but what if those same fumes later go on to save much later generations from having to endure otherwise inevitable ice ages?

  At first, this ethical dilemma might seem outlandish, a silly kind of joke. Speaking of it too flippantly feels disrespectful of those who may suffer from the climatic changes of today and in the near future. It also feels like tossing raw meat to the habitual contrarians who seek any excuse to avoid controlling fossil fuel consumption. But the facts are plain, and I believe they’re worth considering carefully.

  Unfortunately, the large time scales involved in this subject complicate discussions of it. It’s much easier to imagine what climate change might do to ourselves or our grandkids than what it might do to people 130,000 years from now, and this can make it difficult for some individuals to take the matter seriously. For them, weighing the value of their own lifetimes against those of unknown citizens of the far future is as ridiculous as weighing the value of a living child against that of a cartoon character; such distant people and times are simply too remote to seem real.

  On the other hand, many of us do enter that deep pool of inquiry when we consider doing things for the sake of future generations, though our entrance is usually more of a toe dabble than a dive. In fact, thinking and acting on behalf of future-dwellers isn’t the simple endeavor that it may seem to be, especially if you don’t restrict your attention to those closest to us in space and time.

  For one thing, you have to decide who those beneficiaries will be. Does your list include everybody who will be alive in, say, 2500 AD or just a select subset of them? You might be willing to give up your gas-guzzling car in order to keep the climate of a direct descendant’s world similar to that of your own. But what if that choice also harms someone else, perhaps by making some future nation much wetter or drier than it would otherwise be: will you favor your own lineage over those of others? And if you choose to favor your own descendants, you still have to decide which ones to focus on because various generations will prefer different things at different places and times in the future.

  If we imagine the Anthropocene in its entirety, it gives us a very large and diverse collection of future people to consider. Many of them will inhabit a warming world, but most will live on the long cooling tail-off of atmospheric CO2 recovery. Perhaps citizens of 130,000 AD might decide that, after so many millennia of ice-free oceans and high-latitude commerce, they’d rather keep things the way they are rather than let CO2 concentrations return to preindustrial levels, particularly with a new ice age looming. Maybe by then our long-lived carbon emissions will have begun to seem less like pollution and more like insurance against global cooling.

  Then again, maybe not. But who are we to decide their fate, anyway?

  We will be messing with planetary temperatures for a very long time, well past the temporal limit of 2100 AD, but we still have time to head off the most extreme consequences if we choose to do so with a long-term view of the future in mind. One of the most important decisions that our generation will ever make is the critical choice between a relatively moderate scenario in which we quickly replace fossil fuels with other energy sources and an extreme one in which we burn through our remaining cheap petroleum and then go on to consume our coal reserves as well. But in either case, one thing is becoming increasingly clear. Humankind is going to face a long-lasting array of environmental challenges of its own making as the Anthropocene runs its course.

  2

  Beyond Global Warming

  Carbon is forever.

  —Mason Inman, Nature Reports Climate Change,

  November 20, 2008

  Fossil carbon threads a common causal link through the Anthropocene from long-term warming to sea-level rise, and it has already made some enormous environmental changes inevitable. But the details of exactly how they could play out are still largely up to us. As luck would have it, we who live in the twenty-first-century will be powerful decision makers in this new Age of Humans. Before us lie several possible routes, and we’re going to select one of them on the basis of how much fossil fuel we choose to burn during the next hundred years or so. As we struggle to make that choice wisely in the midst of our self-made carbon crisis, we need to understand as much as possible about the ways in which our actions today may influence the long-term future of the world.

  In these early days of human-driven climate change, global warming is on center stage. But that is only the foreword to an immensely long tale in which climate change will mostly come to mean global cooling, albeit from artificially boosted temperatures that will remain higher than those of today for thousands of years. According to an increasingly influential group of climate visionaries whom I’ll introduce shortly, the slow natural processes that must gradually erase our carbon footprints will take not just a few more centuries but many millennia to lower CO2 concentrations to their normal ranges. As they drop, artificially high greenhouse temperatures will also fall in response. But those changes will occur far more slowly than most of us yet realize. A full return to preindustrial conditions will take tens of thousands—perhaps even hundreds of thousands—of years.

  It’s not difficult to visualize the basic trajectory of things to come if you keep in mind the following maxim: What goes up must come down. I will assume here that you already know how increasing concentrations of greenhouse gases such as carbon dioxide (mainly from power plants, vehicles, and factories) and methane (farms, landfills, sewage, mines, pipelines) raise temperatures by trapping solar energy in the atmosphere as it re-radiates from Earth’s sunlit surface in the form of heat; detailed descriptions of that process are now ubiquitous online and in print. But greenhouse gas concentrations in the air can’t increase forever because there are only a finite number of accessible carbon atoms i
n the world. And temperatures can’t rise indefinitely, either; even the worst possible scenario won’t make the planet burst into flames. An eventual peak and turnaround in the modern warming trend are therefore inevitable.

  Most of us are still so focused on the present pattern of warming that it can be easy to forget the obvious, that entirely different modes of change must lie ahead. At some point, the direction of current trends will shift into reverse and produce a staggered climate whiplash effect. Coping strategies that have been developed in response to warming will become obsolete, or even liabilities, as the adaptive momentum gained in adjusting to rising trends pushes onward while the environmental setting itself lurches off in new directions. As future temperatures pivot into cooling mode, not only will Earth’s inhabitants have to adjust to environmental change; they’ll have to adjust to a complete reversal in the very nature of that change.

  But it won’t be quite as simple as a single episode of whiplash might be. The loose connections among various components of the air-land-ocean system will cause delayed reactions to the changes driven by the rise and fall of greenhouse gas concentrations. Those components will act like a string of mountaineers loosely roped together; if the lead climber slips from an icy crag, the remaining team members will be pulled one by one after intermittent moments of slack time.

  You need no computer program to predict the basics of this coming stage of global change; deducing its general outline is largely a matter of common sense, though the specifics of timing and intensity are another matter. Sooner or later, we’ll stop emitting so many greenhouse gases, either by choice or by running out of affordable fossil fuels. After our emissions rate peaks and begins to decline, the atmospheric CO2 curve will also crest and then begin to fall back toward preindustrial levels. All else will follow the lead of that CO2 pulse.

  The next wave of whiplash will come as global average temperatures peak at some thermal maximum and then drop back down in a delayed reaction to the CO2 reversal. The very idea of an end to global warming may come as a surprise if you have limited your thinking on this topic to the short term, but it simply can’t go on forever. The greenhouse effect will inevitably weaken in response to the future decline of fossil fuel pollution, and that will bring temperatures back down.

  Under the cooling-but-still-warm conditions that follow the thermal peak, polar ice sheets will continue to shrink and the heated oceans will continue to swell in their basins like yeasty dough in a warm kitchen. But eventually, the rising seas will reach some peak elevation and then begin to fall along with temperature. So, too, will the acidity levels of the oceans.

  To examine that bumpy road ahead more closely, we must look far beyond 2100 AD into the realm of reasonable speculation. And to put approximate dates and magnitudes on these coming waves of change, we can now be guided by pioneering scientists who probe the future with new breeds of global climate models.

  But how can we trust such models if forecasters can’t even predict local weather just a few weeks in advance? True, computer models are to real climate as model airplanes are to fighter jets, but we aren’t trying to make far-future predictions about weather, which is a short-term, localized, and rather chaotic phenomenon. Instead, we’re talking about basic, long-term, global-scale climate, which is averaged over many years and over large areas of the planet. We’re only asking for broad generalizations here, and ones that are based upon sound scientific principles. For example, no responsible climatologist would seriously proclaim that July 29, 5000 AD in New York City will be a bright and sunny day, but we can be reasonably sure that dawn will arrive from the east on that morning and that water will neither freeze nor boil under the conditions that July would be likely to bring to that location.

  A key concept underlying these projections is the conservation of matter. When we shut down the spigot of air pollution, our emissions won’t simply vanish. They may drift downwind, but they still exist somewhere on this bubble of a planet. We may watch chimney smoke dissipate, and we speak of throwing trash “away,” but the atoms in that smoke and that garbage are neither created nor destroyed by our normal daily behavior, even though we may have forgotten about them.

  Skilled modelers can follow the wanderings of our carbon emissions in computer-generated worlds like trackers on a fugitive’s trail. After all, there are only so many places for a carbon atom to go. It can drift freely in the air for many years, but it will eventually take up residence elsewhere. It might dive into the sea before reentering the air on the other side of the world. It might be sucked into the tiny pores of an oak leaf and spend a tree’s lifetime bound into the structures of bark or wood. Later still, it might dissolve into a raindrop that splashes against a granite boulder and works its way into the crystal lattice of a feldspar grain, helping it to crumble into dirt. And today it might be lodged in the fleshy tip of your nose, anticipating its next move to some other earthly destination. The best computer models take this shape-shifting into account as they probe the future.

  One of the earliest and most prolific sources of information on this topic is David Archer, a climate-savvy oceanographer at the University of Chicago with the professional resumé of someone with too much inquisitive energy to fit into a single lifetime’s work schedule. Using a new generation of sophisticated computer models with names like CLIMBER (Climate and Biosphere), GENIE (Grid-Enabled Integrated Earth System), and LOVECLIM (a composite of five other model names), Archer and a growing corps of like-minded investigators around the world are tracing and refining predictive templates for a future that is flooded with the vapors of combusted coal, oil, and natural gas.

  “The idea that a sizable fraction of our carbon dioxide could stick around for hundreds of thousands of years hasn’t reached mainstream consciousness yet,” he told me in a recent phone conversation. And that goes for most of the scientific community as well, although the idea is percolating in ever wider circles these days. This field of inquiry is so new that you can still count most of its foundational publications on your fingers. Kirsten Zickfeld, a climatologist and computer modeler at the University of Victoria, British Columbia, acknowledges Archer’s groundbreaking role in the field but adds one important reason why this kind of research was not being conducted earlier. “We simply didn’t have the right tools for it until just a few years ago,” she explained to me. “The models have to mimic the cycling of carbon in and out of various habitats along with the climatic changes. Older simulation systems weren’t fast enough to handle so much complexity.” These upgraded models, in turn, are rapidly upgrading the time scales that we imagine the future on. “We can now see the irreversibility of the impacts that we’re having on the planet today,” she continued. “Our carbon emissions won’t be gone nearly as quickly as we once thought. In fact, they’ll stick around pretty much forever.”

  Simulations of our near-term carbon future present such a diverse collection of twenty-first-century trajectories that it can be difficult to know which ones to focus on as we hitch them to the long-term outlooks that Archer, Zickfeld, and their associates are generating. Rather than try to sort through all of them here, I’ve selected a representative pair of carbon emissions scenarios from the last assessment report of the Intergovernmental Panel on Climate Change (IPCC), one of them relatively moderate and one extreme, to bracket the most commonly accepted range of paths that lie before us. They will provide the basics of what you need to know about our main options for the near future. I’ll then offer much longer-term views of what could follow these two opening acts, based upon the outputs of CLIMBER and other models. The results of those simulations vary somewhat in their specifics, but in general they are remarkably consistent.

  In the moderate scenario, we aggressively limit CO2 concentrations to a peak of 550 to 600 ppm. The IPCC calls this low-growth emissions scenario B1. The B1 scenario is “moderate” only in relation to the more extreme one that follows, and many climate activists are currently focused on holding greenhouse gas co
ncentrations to a much lower 350 ppm, a level which is considered likely to prevent societally disruptive human-driven climatic changes. I support and am inspired by 350.org and related movements, but we are already well past that preferred milepost on the rising carbon curve, and most of the climatologists I have spoken to believe that we won’t be going back to those concentrations any time soon. The choice of B1 for the low end of the scenario spectrum is based more on a sense of hard-core realism than on desire. The 350 ppm concentration is an excellent goal to aim for, but 550 to 600 ppm is probably what we’d really end up with after taking such aim.

  In this so-called moderate case, we switch to nonfossil fuels as soon as possible but still end up adding another 700 gigatons (Gton; I billion metric tons) of carbon pollution to the 300 Gtons we have already released since the Industrial Revolution, bringing us to a grand total of 1,000 Gtons. Although the environmental changes that are likely to follow such a release will be large and long-lasting, and even though it would be preferable to avoid such a path altogether, this hypothetical situation is meant to approximate a realistic best-case—or rather, least-unwelcome—scenario for our Anthropocene future.

  Scenario 1: A Moderate Path

  We can’t realistically expect fossil fuel consumption to stop everywhere all at once, so let’s say that our rate of CO2 emissions reaches its peak around 2050 AD and finally fades out altogether by 2200 AD.

  In that case, atmospheric CO2 concentrations climb from today’s value of 387 ppm to a peak of 550 to 600 ppm, roughly twice the preindustrial level of the 1700s, some time between 2100 and 2200 AD. The oceans gradually absorb much of that excess CO2, which becomes carbonic acid in solution and changes the chemistry of seawater, making it increasingly corrosive to the limy shells of many marine organisms, especially in colder waters at high latitudes and great depths.