Every other Friday on Morning Edition, the Outside/In team answers a question from a listener about the natural world. Right now, the theme is “What if?”
David, from Fairbanks, Alaska, is wondering:
“What if Earth’s atmosphere reaches a CO2 concentration of 1,200 ppm? My understanding is that this will be a critical tipping point for life on Earth. I’d like to know what changes in our behavior will be absolutely necessary for survival. What should governments, corporations, communities, and individuals and their families expect to do about it?”
SSP5
Bear with me for a moment, because I’m going to have to throw some numbers at you to help answer this one.
The Intergovernmental Panel on Climate Change, or IPCC, has outlined a handful of possible climate futures. Each one depends on world leaders (governments, corporations, etc.) taking action to curb emissions and drive global temperatures back down toward pre-industrial levels. The most aggressive scenario, where we successfully reduce emissions, is called ”SSP1.” And the worst-case scenario, where we essentially do nothing, is called “SSP5.”
SSP stands for “Shared Socioeconomics Pathway.” SSP5 isn’t so much what scientists think will happen — it’s a baseline to help measure what we can and should do to prevent it from happening. And even then, there are built-in assumptions that are a matter of robust debate.
Regardless, there’s a chance that a scenario like this would see atmospheric carbon dioxide doubling to 1200 ppm (parts per million) or more. But what does that actually mean?
Ironically, I can’t give you a precise picture. Nobody can.
Worst case scenario
Luke Kemp is a research affiliate at the Center for the Study of Existential Risk, in Cambridge, England.
“Currently, worst-case scenarios are dangerously understudied,” he said.
Past a certain tipping point, there simply aren’t many studies that model how bad global conditions could get. The few that do exist are highly theoretical. Kemp said there is a scientific incentive to focus on lower emissions. He also thinks there is a good reason to entertain doomsday scenarios as well.
“With better science, we can actually have better discussions about these worst-case scenarios," he said. "Right now, people often revert to this doomsday talk because they can't rely upon good evidence and good studies. So I think this actually improves the discourse rather than just reverting back to climate doomerism.”
Okay, so let’s talk about it — and, remember, this is theoretical.
In a worst-case scenario, the polar ice caps would melt completely, ushering in 65 meters of sea level rise over a few thousand years. That’s enough to reshape coastlines around the globe. (The entire state of Florida would basically be underwater.)
On a shorter time scale, we’d see mass extinctions worse than the worst mass extinctions Earth has ever seen. For comparison, the Permian-Triassic Extinctionwiped out some 90 to 95% of all species on the planet.
Extreme heat becomes the norm, and growing crops across huge swaths of the globe would become virtually impossible.
Heat and runoff would make oceans more acidic and anoxic (lacking oxygen) and very inhospitable to supporting marine life.
Scientists have theorized about other (again, hypothetical) climate feedback loops that trigger some truly nightmarish images. Lightning strikes could trigger explosions of methane gasmore powerful than nuclear weapons, for example. If ocean temperatures exceed 120 degrees, we could see a new class of storm called a “hypercane” many times more powerful than the worst hurricanes on record.
“What you get,” Kemp said, “is a fairly silent, life-depleted, hellish landscape made up of purple oceans and a slightly green-tinged sky as well.”
So. Could humans survive?
Algae, seaweed and rats
If humans went extinct, Kemp doesn’t think it would be the climate that put the nail in the coffin. It would be the knock-on effects: financial disruption, the collapse of industrial processes, war and social unrest.
But those things aside, there are a few adaptations that we’d have to make to survive a much hotter world. First, Kemp said, we’d migrate to places like Canada, the Arctic, and maybe even Antarctica. Problem is, we don’t actually know whether the soil in some of those places will be any good for food production.
“The wackiest thing one can imagine,” Kemp said, “is that we actually start relying upon other staple food sources, in particular things like algae, seaweed, and potentially even actually growing mushrooms en masse…and potentially eating things like rats, much more kind of hardy species."
Depending on where they live, Kemp thinks people might be housed in bunkers or underground systems. They could bioengineer their bodies to better survive extreme conditions, or invent new cybernetic implants. Kemp thinks desalination plants to make fresh water could become more common.
All this is to say, we have squarely entered the realm of science fiction. As for governments, corporations, and families, who’s to say? Looking towards dystopian movies and books (like "Mad Max" or "The Road") you might think humans will be pretty much at their worst in this scenario.
Kemp disagrees.
“I think that's unlikely, and I think particularly based on my study of previous societal collapses, if anything, there's a good chance that you might even see more pro-social democratic forms of governance happening," Kemp said.
It’s important to remember that, while most experts don't’ really dispute the basic facts about climate change, there is a lot of uncertainty around these more extreme hypotheticals. For now, the most important thing scenarios can do is push us to make changes, so that’s all they’ll ever be.
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