Can a 4°C Earth Support 10 Billion People? - by Joe Romm

I personally doubt homo sapiens will go fully extinct. The more important question for me is whether the planet can support upwards of 10 billion people post-2050 given that we have already overshot the Earth’s biocapacity — and the overshoot gets worse every year.

Most significantly, we are in the process of destroying a livable climate upon which so many species, including our own, rely.  We are currently on a trajectory to warm the planet 4°C (7°F) or more this century and then continue warming in the next.  In 2011, the UK Royal Society devoted a special issue of one of its journals to “Four degrees and beyond: the potential for a global temperature increase of four degrees and its implications.”  The concluding piece warned:

“In such a 4°C world, the limits for human adaptation are likely to be exceeded in many parts of the world, while the limits for adaptation for natural systems would largely be exceeded throughout the world.”

In particular, “drought and desertification would be widespread” and we’d see “large areas of cropland becoming unsuitable for cultivation, and declining agricultural yields.”  At the same time, we’d “also rapidly be losing [the world’s] ecosystem services, owing to large losses in biodiversity, forests, coastal wetlands, mangroves and saltmarshes, and terrestrial carbon stores, supported by an acidified and potentially dysfunctional marine ecosystem.”

Can such a world support 10 billion people?

As for biodiversity, a 2015 study in Science said we may lose one-sixth of all species to extinction if we warm 4°C.  “Other experts said the real toll may turn out to be even worse,” reported the New York Times.  The paper quoted evolutionary biologist John Wiens warning the number of extinctions “may well be two to three times higher.”

As I reported a few weeks ago, another 2015 study in Science concluded that the Permo-Triassic extinction 252 million years ago (“the greatest extinction of all time”) happened when massive amounts carbon dioxide were injected into the atmosphere, first slowly and then quickly (driven by volcanic eruptions).  The researchers found “During the second extinction pulse, however, a rapid and large injection of carbon caused an abrupt acidification event that drove the preferential loss of heavily calcified marine biota.”  This extinction killed over 90 percent of marine life and wiped out some 70 percent of land-based animal and plant life.

A 2014 review article in the journal Science led by Duke conservation ecologist Stuart Pimm, “The biodiversity of species and their rates of extinction, distribution, and protection,” concluded, “Current rates of extinction are about 1,000 times the background rate of extinction. These are higher than previously estimated and likely still underestimated.”

The current mass extinction is due to a combination of factors, many driven by humans, including habitat destruction and over-fishing and over-hunting.  A number of aspects of climate change have begun contributing to species extinction, but what is of most concern to biologists today is that as the rate of global warming speeds up in the coming decades, the climate may well change too quickly for many if not most species to adapt.

Read more at Can a 4°C Earth Support 10 Billion People?