If every nation that has so far pledged to cut down on its carbon emissions made good on its promises, the global average temperature would still rise 3.5˚ Celsius by the end of the century. According to a new study from MIT Sloan and Climate Interactive, even with the hard-won commitments from nations around the world, we're still on track for "catastrophic" levels of planetary heating. If, that is, the governmental targets aren't stepped up, or paired with other aggressive efforts.
In advance of the upcoming climate talks in Paris this year, which many consider the world's best shot at cementing an agreement to limit global warming, nations have begun submitting what are known in UN-speak as Intended Nationally Determined Contributions (INDCs).
These are basically declarations of intent for how a given country aims to reduce or mitigate its carbon emissions—Norway, for instance, is pledging to reduce its carbon emissions by 40 percent by 2030. The US is aiming for a 28 percent CO2 reduction by 2025. China, meanwhile, again made waves when it announced it would match the US's fuel efficiency standards and launch a new cap-and-trade system for reducing pollution as part of its plan.
It should speak to the scope of the climate problem that even with all those reduction commitments on the books, we're headed for what scientists say are civilization-threatening levels of warming. To reach that conclusion, MIT rounded up all such pledges that are on the books, and analyzed the total impact they'd have on temperature rise.
The study concludes that the commitments, if fulfilled, will indeed make a serious difference—they will prevent an entire 1˚C of temperature rise—but that they won't prevent the global thermostat from spiking past 2˚C; the benchmark that's long been considered the threshold for dangerous warming.
The breakdown, according to MIT and CI, looks roughly like this:
There at the bottom is the "2˚C Path"—that's the target scientists say we should be aiming for to prevent major destabilization of the climate system. It's still a lot of temperature rise, and a lot of locked-in pain—we've already got nearly 1˚C under our belts, as of now—but it would, hopefully, mitigate the worst impacts of global warming. If we hit 2˚C, which we probably will, there will major problems—coastal flooding, worsened droughts and exacerbated flooding, human migration, and up to 30 percent of the world's species dying off.
But passing 3˚C is much, much worse. The middle graph models the temperature rise of the world in nations stick to their pledges and start drawing down carbon emissions in earnest. And at 3.5˚C (6.3˚F), it's well beyond the threshold.
Skeptical Science, a scientist-run compendium of climate science, offers a grim synthesis of what would likely happen in that scenario:
"At 3–4°C warming, widespread coral mortality will occur (at this point corals are basically toast), and 40–70% of global species are at risk as we continue on the path toward the Earth's sixth mass extinction," the environmental scientist Dana Nuccitelli explains. "Glacier retreats will threaten water supplies in Central Asia and South America. The possibility of significant releases of CO2 and methane from ocean hydrates and permafrost could amplify global warming even further beyond our control." Those so-called feedback loops could then rapidly accelerate warming at a rate as of yet unseen.
"Sea level rise of 1 meter or more would be expected by 2100, with the possibility of destabilization of the Greenland and West Antarctic ice sheets, which would cause much more sea level rise and flooding of coastal communities."
It's a full-scale planetary disaster, basically.
Worst of all, of course, is business as usual. The talks fail, there's no treaty, and we go on burning fossil fuels like it's 1999. That lands us at 4.5˚C, or 8.1˚F, worth of temperature rise by the end of the century, if we maintain the status quo trajectory. That's also a nightmare scenario.
The World Bank, not exactly a liberal institution, did a report analyzing the outcome of a 4˚C+ world: "4°C scenarios are potentially devastating: the inundation of coastal cities; increasing risks for food production potentially leading to higher under and malnutrition rates; many dry regions becoming dryer, wet regions wetter; unprecedented heat waves in many regions, especially in the tropics; substantially exacerbated water scarcity in many regions; increased intensity of tropical cyclones; and irreversible loss of biodiversity, including coral reef systems." More of the same, more of the worse.
Of course, some scientists say even 2˚C of warming would be a "disaster."
But it's worth honing in on the silver lining here—1˚C worth of reductions, the amount nations have already pledged to uphold—is a major achievement, and a serious step forward from what has in the past been a tortured, laborious, and unproductive negotiation process. There's reason to believe, with the costs of renewable power falling fast, and a spirit of international cooperation slowly coalescing around the climate problem, that a 2˚C target isn't out of reach.