By David Wallace-Wells
Just two years ago, amid global fanfare, the Paris climate accords were signed — initiating what seemed, for a brief moment, like the beginning of a planet-saving movement. But almost immediately, the international goal it established of limiting global warming to two degrees Celsius began to seem, to many of the world’s most vulnerable, dramatically inadequate; the Marshall Islands’ representative gave it a blunter name, calling two degrees of warming “genocide.”
The alarming new report you may have read about this week from the UN’s Intergovernmental Panel on Climate Change — which examines just how much better 1.5 degrees of warming would be than 2 — echoes the charge. “Amplifies” may be the better term. Hundreds of millions of lives are at stake, the report declares, should the world warm more than 1.5 degrees Celsius, which it will do as soon as 2040, if current trends continue. Nearly all coral reefs would die out, wildfires and heat waves would sweep across the planet annually, and the interplay between drought and flooding and temperature would mean that the world’s food supply would become dramatically less secure. Avoiding that scale of suffering, the report says, requires such a thorough transformation of the world’s economy, agriculture, and culture that “there is no documented historical precedent.” The New York Times declared that the report showed a “strong risk” of climate crisis in the coming decades; in Grist, Eric Holthaus wrote that “civilization is at stake.”
Because the numbers are so small, we tend to trivialize the differences between one degree and two, two degrees and four. Human experience and memory offers no good analogy for how we should think about those thresholds, but with degrees of warming, as with world wars or recurrences of cancer, you don’t want to see even one.
At two degrees, the melting of ice sheets will pass a tipping point of collapse, flooding dozens of the world’s major cities this century. At that amount of warming, it is estimated, global GDP, per capita, will be cut by 13 percent. Four hundred million more people will suffer from water scarcity, and even in the northern latitudes heat waves will kill thousands each summer. It will be worse in the planet’s equatorial band. In India, where many cities now numbering in the many millions would become unliveably hot, there would be 32 times as many extreme heat waves, each lasting five times as long and exposing, in total, 93 times more people. This is two degrees — practically speaking, our absolute best-case climate scenario.
At three degrees, southern Europe will be in permanent drought. The average drought in Central America would last 19 months and in the Caribbean 21 months. In northern Africa, the figure is 60 months — five years. The areas burned each year by wildfires would double in the Mediterranean and sextuple in the United States. Beyond the sea-level rise, which will already be swallowing cities from Miami Beach to Jakarta, damages just from river flooding will grow 30-fold in Bangladesh, 20-fold in India, and as much as 60-fold in the U.K. This is three degrees — better than we’d do if all the nations of the world honored their Paris commitments, which none of them are. Practically speaking, barring those dramatic tech deus ex machinas, this seems to me about as positive a realistic outcome as it is rational to expect.
At four degrees, there would be eight million cases of dengue fever each year in Latin America alone. Global grain yields could fall by as much as 50 percent, producing annual or close-to-annual food crises. The global economy would be more than 30 percent smaller than it would be without climate change, and we would see at least half again as much conflict and warfare as we do today. Possibly more. Our current trajectory, remember, takes us higher still, and while there are many reasons to think we will bend that curve soon — the plummeting cost of renewable energy, the growing global consensus about phasing out coal — it is worth remembering that, whatever you may have heard about the green revolution and the price of solar, at present, global carbon emissions are still growing.
None of the above is news — most of that data is drawn from this single, conventional-wisdom fact sheet. In fact, nothing in the IPCC report is news, either; not to the scientific community or to climate activists or even to anyone who’s been a close reader of new research about warming over the last few years.