While much of the world has been bickering over whether climate change is real or not, climate scientists have been going about their research as usual. But what they have been discovering is revolutionary. Not only is human-driven climate change real; it's even more serious than we thought.
Until now, most views of future temperature trends have been limited to this century, as if 2100 AD marked the outer edge of a world beyond which we dare not probe. The latest research pushes past that arbitrary temporal boundary to ask "what happens next?" According to investigators such as David Archer, an oceanographer and climate modeler at the University of Chicago, the heat-trapping gases that we release now will linger for tens of thousands of years, long enough to interfere with future ice ages. From that perspective, global warming is essentially forever—at least in human terms.
How can this be? Earlier studies have suggested that we're tracing a trail of carbon footprints just a few centuries long, but more sophisticated models and analyses now clearly show otherwise. The logic behind this is surprisingly simple, amounting to common sense combined with a truly long-term perspective. Carbon dioxide doesn't just disappear when it leaves our tailpipes and smokestacks—it has to go somewhere. And people like Archer follow the invisible tracks of that carbon to find out where it eventually goes.
"The main destination is the oceans," he explained over the phone. "Carbon dioxide dissolves in seawater, and that's where most of it will go within the next several millennia." Unfortunately, when CO2 dissolves into seawater it forms carbonic acid, thereby threatening everything with acid-soluble hard parts, from clams to crabs to corals. Such ocean acidification is already happening, and it will grow progressively worse the more CO2 we pump into the air.
"The oceans can only absorb so much carbon dioxide, though, so roughly a fifth of our emissions will be marooned in the atmosphere. It will then take many thousands of years for chemical reactions with rocks and sediments to scrub the rest of it away."
The work of Archer and others show that we have an important choice to make during this century. If we switch to carbon-free fuels quickly, our greenhouse gas emissions will keep the world slightly warmer than today for as long as 100,000 years. As unsettling as that may be, the alternative is even more severe. If we burn all remaining fossil fuels, including our huge coal reserves, the warming will be five to ten times more extreme and last five to ten times longer.
In short, we've become a shockingly powerful force of nature. I liken this revelation to the first NASA photos of Earth, from which we learned that we ride a delicate blue bubble through deep space. This equally transformative view of our place in deep time shows that we are also incredibly important. We're now so numerous and our technology so powerful that the effects of our collective actions in coming decades will echo on down through the ages.
And there's more. Near-term global warming will be followed by entirely different environmental challenges. "After our carbon emissions peak and begin to fall back down," Archer continued, "temperatures will also peak and begin to drop, first rapidly as the oceans do their work, and then more slowly as the rocks finish the job." Most of the recovery from our carbon legacy will therefore involve global cooling, albeit from temperatures higher than those of today. And that will bring reversed versions of environmental problems that worry us here and now, including sea level retreat, re-shuffling of rainfall patterns, and eventual re-freezing of formerly ice-free regions.
An ice-free Arctic may seem unthinkable to us now, but by 100,000 AD it will have become normal, even ancient. When climates once again begin to resemble those of today, the re-freezing of the open polar sea may be equally unsettling to our distant descendants who will have come to depend on it. As far-sighted elders notice the first skim of ice forming along some shoreline, perhaps they'll whisper, "I don't remember seeing that before. If this continues, the whole place might freeze over—what a disaster!"
Fortunately, such dark views of our deep future also reveal a few bright spots. For one thing, we've stopped the next ice age. Natural cycles were scheduled to launch it around 50,000 AD, but our lingering fumes will keep the world just warm enough then to save the northern halves of North America and Europe from being bulldozed by mile-thick slabs of ice. Feel better now?
More importantly, we still have time to decide which path we're going to take. If we switch soon to carbon-free energy sources, most cultures, habitats, and species may manage to adapt to the relatively moderate changes that will result over the next 100,000 years. But an uncontrolled carbon-burning spree will melt all polar ice, hoist sea levels by hundreds of feet, and stretch massive warming-then-cooling disruptions over the next half a million years or more.
What's at stake in this big picture? Admittedly, climates and sea levels will eventually recover in either scenario, and Homo sapiens may be resourceful enough to survive somehow as a species. But the free migration that helped animals and plants to adjust to natural climatic shifts of the past will not be so freely available with our settlements, roads, and farms in the way. And if we take the extreme path, there may be no refuge at all for polar bears or other cold-loving creatures, not to mention marine life trapped in the acidifying oceans.
Global warming will last a long time in comparison to the lifespan of a short-sighted human. But extinction is truly forever.
Curt Stager is an ecologist, paleoclimatologist, and science journalist with a Ph.D. in biology and geology from Duke University. His new book is DEEP FUTURE: The Next 100,000 Years of Life on Earth (St. Martin's Press, March 2011).