I’d like to write an article on the children’s climate strike, but such a topic will take time to do well–and today is my wedding anniversary. So I’m giving you another excerpt from the essay at the back of my next novel, since that is already written. I’ll cover the children later this week if I have time, or next week.
In the meantime, you enjoy the following, while I enjoy dinner with my husband.
Essay Excerpt 2: Predicting the Future of the Climate
Readers familiar with New England may notice that the weather in this book seems odd. It is hot in May, the people are preoccupied with the possibility of flooding, and there are a lot of storms. The characters think it all normal. Am I, the writer, trying to depict climate change? Yes and no.
Yes, I had climate on my mind when I wrote this book. The New England climate in the story is not the one that exists today, and I wanted readers to notice. Fiction in the present Age of Rapid Climate Change needs to acknowledge climate as a function of time as well as space: no writer would give Seattle the same climate as Miami, so why depict the past or future with the same climate as the present?
Climate is the set of patterns that weather makes over time, and this story takes place over less than a year: not enough time for any patterns to become clear. That the characters think hot weather in May is normal—not the hot weather itself—suggests the climate has changed, and even that is a poor indicator. Humans are notoriously bad at identifying trends based on personal experience; that is one reason why record keeping and statistics were invented.
It is just as well that the story does not give the reader a good view of the climate. Constructing a scientifically plausible fictional climate—which I would sorely like to have done—is fiendishly difficult if not ultimately impossible. The problem is that climate cannot be predicted by ballpark estimations and back-of-the-envelope calculations. One of the curious traits of complex systems is that no detail can be guaranteed to be too small to matter. The phrase “butterfly effect” describes how the flap of an insect’s wings could cause a hurricane on the other side of the planet. In a picturesque way, the phrase describes a problem that cropped up with the earliest weather simulations: two simulations with nearly identical starting numbers often yielded radically different results (Curtin & Allen 2018). Attempting to simulate a climate without the aid of a supercomputer and a lot of data is, at best, an exercise in fantasy.
If the story were set in a version of the future that climatologists consider likely, my job would be rather more straightforward: just look up the climate projections that have already been done and attempt to synthesize. I did just that for a piece I published online several years ago. But the abrupt, near-term end of fossil-fuel use in my novel has not been subject to much in the way of simulation because no one thinks it likely.
Since I could neither invent nor look up a scientifically plausible climate to use as setting for the story—and since the plot does not allow for depicting the climate directly anyway—I simply wrote any scenes involving weather with three adjectives in mind: “warmer”, “wetter”, and “more extreme”. These are consistent with contemporary predictions for the region over the next century (see e.g. van Oldenborgh et al. 2013), as well as loosely plausible for the various scenarios implied by my story.
Science can’t tell us what the climate for the setting of the book should be, but it can shed light on what Andy thinks it is doing—an important part of his emotional landscape, given who he is. Remember that the field of climatology in his time is very limited. Most of what he understands about the climate is what he remembers from Before.
The reader might think that, since fossil fuel use has stopped, levels of greenhouse gases and average temperatures should both fall—but what might seem obvious is not necessarily true.
As of 2010, combustion of fossil fuels was responsible for about two-thirds of total greenhouse-gas emissions by weight. There are other sources of carbon dioxide however, and there are other greenhouse gasses: notably methane (a much more powerful greenhouse gas than carbon dioxide), but also nitrous oxide and two related groups of gases, the chlorofluorocarbons (CFCs) and hydrofluorocarbons (HCFs) (Edenhofer et al. 2014). In my scenario, carbon emissions from fossil-fuel use are over and have been for twenty years. That does not mean, however, that other kinds of emissions, such as methane from landfills or melting permafrost, stop – at least, not instantly. For reasons I will go into later, some could increase.
To understand the total concentration of each gas in the atmosphere—and how it is likely to change over time—it is not enough to know emission rates. One must also look at rate of loss, which will be different for each gas. Picture running a bathtub with the drain open; whether the tub fills or empties depends on inflow versus outflow.
For most greenhouse gasses, loss (“outflow”) is primarily by chemical degradation occurring at a more or less set rate per gas (Ehhalt 2001). Carbon dioxide is a little more complicated, because it does not degrade this way. Rather, it is absorbed through a number of processes, each with its own rate and capacity.
The fastest way for carbon dioxide to leave the atmosphere is absorption by the oceans’ surface waters. A large amount can be absorbed in just a few decades. Unfortunately, water can only absorb so much, and the oceans’ surface waters have already absorbed a lot; that is why they are becoming increasingly acidic. Of course, a lot more water lies beneath the surface, but the ocean mixing required for it to absorb carbon dioxide does not happen on a human timescale.
After ocean surface waters reach capacity, the next fastest way out of the atmosphere is the chemical weathering of rock, but that, too, does not play out on a human timescale. A big carbon dioxide spike takes tens or even hundreds of thousands of years to flatten out (Ciais et al. 2013).
Scientific articles on potential recovery from climate change tend not to mention absorption of carbon by organisms, even though it is organisms that sequestered the carbon in fossil fuels in the first place. I would guess this is because the sequestration process—including the accretion of new oil, gas, and coal deposits—is so very, very slow.
Andy confidently asserts that carbon dioxide levels are falling—quickly enough that he expects to be able to study the ecological results of the change himself. He is very excited. Presuming he is right, that could be taken to mean that ocean surface waters have not, in fact, reached capacity; but another possibility presents itself.
While the formation of fossil-fuel deposits takes place on a geological timescale, living plants are a different matter. They, too, sequester quantities of carbon, and many of them, including large trees, can grow relatively quickly. Individual plants are not considered carbon sinks because, when the plant dies, all that carbon is released again; but entire plant communities can, indeed, be carbon sinks. Where one tree in a forest dies, another can grow and take up the carbon in turn. Indeed, deforestation is considered an important source of carbon dioxide emissions—so, logically, the growth of large, new forests should have the opposite effect.
I have never heard reforestation suggested as a way for carbon dioxide levels to drop, but perhaps that is because relevant discussions typically assume that the human population is going to stabilize—not fall. With so many people and associated agriculture and infrastructure in the way, there is not much room for new forests to grow. But Andy has experienced a radical reduction in the population—the reader learns that, at least in the US, the population is about one tenth of what it had been; the rest of the world is presumably similar. Per capita resource use also appears to have fallen. That leaves a lot of room for new trees.
Could continental-scale reforestation cool the climate? There may be precedent.
When Europeans first came to the Americas, they brought along diseases to which the Americans1 had no immunity. This was not germ warfare (that came later), but the result was dramatic, continent-wide population loss and widespread societal collapse (Wessels 1997). Forests grew in places that had previously been cleared. The idea that North America was a pristine wilderness prior to European conquest is partly due to the overgrown, depopulated mess that colonial explorers found in the wake of the terrible pandemics (Wessels 1997).
The post-contact pandemics are history’s closest analogue to the present story. Contagious disease really did cause the end of a world. It also caused a large-scale reforestation event coincident with changes in atmospheric carbon-dioxide levels and a global drop in temperatures (Dull et al. 2010), the second, more severe, phase of the so-called Little Ice Age. The first phase may be partially attributable to the Black Death in Europe, another pandemic that triggered large-scale reforestation (Hoof et al. 2006).
The timing of events does not support either pandemic as the sole cause of cooling. Other explanations and possible contributing factors have been advanced, and it is far from clear what role—if any—each played. Nevertheless, respected experts have taken seriously the idea that continental-scale reforestation could be enough to cool the planet, suggesting that global reforestation now could change the climate.
Of course, carbon sequestration by reforestation only works if the forests that once existed can grow back. History offers examples of cleared forests that did not return, despite apparent opportunity, for reasons like soil loss (Curtin & Allen 2018), and forests all over the world are starting to die from climate change itself, or from stresses made worse by climate change. Some forests—notably in the tropics—already have become net producers of carbon dioxide, and many more across the world may follow suit as climate change worsens and dieback exceeds growth (Allen 2009). Dying forests could even release enough carbon dioxide to speed climate change and kill even more forest, but whether we have reached that nightmare bifurcation point, or might reach it soon, is unclear.
So, in Andy’s time, the global greenhouse effect may or may not be weakening, depending on various interacting factors—some of which I have mentioned and some not. Several of the relevant questions might well be answerable by anyone with the appropriate mathematical skill and enough data. Others are only answerable with a supercomputer. Still others might not be answerable at all.
Even assuming that the greenhouse effect is weakening in Andy’s time, whether the planet is cooling yet is another question. If greenhouse gas levels simply stabilize, warming will continue for several decades, perhaps 30 to 50 years (Mann & Kump 2015), because the climate needs time to adjust to a stronger greenhouse effect. If the greenhouse gas levels then drop, cooling will occur—but I have not been able to learn how quickly that cooling happens. Logic suggests that if the greenhouse effect weakens before the temperature stabilizes, cooling will begin sooner than it otherwise would, but I have not found confirmation of that principle, either.
But even the onset of cooling will not necessarily undo the damage done by rapid warming. In fact, Earth may continue to deteriorate for some time. Biodiversity loss, like climate change, has a time lag. Evidence from Europe suggests that extirpations peak at least a hundred years after major habitat loss, a delay referred to technically as extinction debt (Curtin and Allen 2018). Ice, likewise, requires time to melt, as anyone knows who has ever enjoyed a drink with ice on a hot day. Big chunks of ice take longer than small ones, and so the massive glaciers of Greenland and Antarctica could go on melting for a very long time before the “melting debt” already accumulated is paid. Undoing such damage might not be possible on any time-scale—when complex systems change, the change is often permanent.
But the irreversibility of change is not the same thing as hopelessness. The sooner the greenhouse effect weakens, the less debt will accumulate and the sooner the new anti-entropic phase can begin. We cannot go back, but we can go on.
So here is Andy, twenty years after the collapse of the world he once knew, in a climate that seems vaguely consistent with the predictions he remembers, but it’s hard to be sure. He knows that soon the world must diverge from prediction, if it hasn’t diverged already. Perhaps the planet will cool, wildlife habitat will expand dramatically, and he will live to see the beginnings of regrowth. Then all Andy’s losses, all the personal tragedy and tumult he has been through, will mean something: the unavoidable side effects of repairing the world that he loves. Alternatively, forest die-back, or some other destructive feedback loop, could render rapid climate change self-perpetuating. The sacrifice of nine-tenths of humanity might yet prove to be too little, too late.
Andy is aware of these possible alternatives, but in the year in which we meet him, he does not yet know which scenario is playing out.
Allen C.D. 2009. Climate-induced forest dieback: an escalating global phenomenon? Unasylva 60: 231—232, 43—49.
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