Nov 27, 2019 1:00 PM

Our Planet May Be Barreling Toward a Tipping Point

A thawing Antarctica, a transforming Amazon, and other devastating changes may be more likely than scientists previously believed.

a melting ice sheet in Greenland from above

When we’re talking about social justice, a tipping point is a beautiful thing—a court case that shifts public opinion, for example. For a species, a tipping point can spell doom, as an environmental catastrophe pushes a population to the brink. When it comes to climate change, there isn’t just one tipping point but many that scientists are increasingly pulling into view.

Today in the journal Nature, a group of researchers argues that we're closer to tipping nine climate demons than previously believed, and that we're already starting to see some associated effects. “We argue that the intervention time left to prevent tipping could already have shrunk towards zero, whereas the reaction time to achieve net zero emissions is 30 years at best,” they write. “Hence we might already have lost control of whether tipping happens.”

We can still, however, act to lessen the damage. The bet we have to make is clearer than ever, but time is running out. “How are we going to look back in half a century’s time and regret the fact that we've built a more sustainable, flourishing future for many more generations to come?” asks lead author Tim Lenton, director of the Global Systems Institute at the University of Exeter. “Instead of just hanging in there with finite reserves of fossil fuels, and sort of embracing the apocalypse.”

The tipping points are grouped into three main categories.

Ice

Think of a climatic tipping point, like the accelerating melting of Greenland’s ice sheet, as a chair. In its normal, stable state, the ice sheet is intact—a chair standing upright. “If you balance the chair backwards, you can find a sort of tipping point, where a little nudge in one direction or the other can determine whether the chair falls,” says Lenton. On its back is the alternate state, in which Greenland’s ice sheets melt until the system reaches a new equilibrium, and the chair just lies there sadly.

Such a tipping is already underway in both East and West Antarctica, argue Lenton and his colleagues. Here, ice and ocean and bedrock meet at so-called grounding lines. These lines are collapsing, and “it could destabilize the rest of the West Antarctic ice sheet like toppling dominoes,” the researchers write, “leading to about 3 metres of sea-level rise on a timescale of centuries to millennia.”

Land

On land, matters are equally grim. Deforestation in the Amazon leads to a terrifying cascade of ecological consequences: Chopped-up forests dry out along their exposed edges, providing ample fuel for wildfires set intentionally by ranchers clearing land. Thus we simultaneously lose the Amazon as a sequesterer of carbon, and the atmosphere takes on more carbon from the smoke. A tipping point of runaway effects could come once between 20 and 40 percent of the forest cover is lost, the researchers say, as the system switches from wet to dry, more like a savanna.

Up in the Arctic, which is warming twice as fast as the rest of the planet, wildfires are raging like never recorded before. Boreal forests are dying off, potentially tipping from a net carbon sink into a net carbon source. Peatlands, which store massive amounts of carbon in the ground, are drying out and burning, releasing still more CO₂. Thawing permafrost is doing the same, only with methane, a far more potent greenhouse gas. More emissions means more warming, as tipping sets in around the world.

Sea

In the oceans, climate change is stressing coral reefs to their limits. When temperatures climb, the corals release the symbiotic algae that help them produce their energy, thus bleaching themselves. Combined with ocean acidification and pollution, an increase of 2 degrees C in the global average temperature could mean the loss of 99 percent of tropical corals.

Offshore, circulation in the Atlantic Ocean has slowed by 15 percent since the middle of last century. Ice melting in Greenland could be slowing the circulation, leading to the destabilization of the West African monsoon, which in turn could trigger droughts. This could also further dry the Amazon and lead to the buildup of warm water in the Southern Ocean, which could further melt ice in Antarctica. Basically, a tipping point triggering a plethora of knock-on effects.

These tipping points don’t exist in isolation; many of them interact and reinforce one another. Given their interconnected nature, modeling them requires making assumptions, since there’s just no way to perfectly capture systems this monumentally complex. That introduces uncertainty into the predictions.

As a result, not all researchers embrace the idea of tipping points. The term suggests a particular number or threshold dividing two worlds, when in reality the before and after aren’t always that clear. “That's where the controversy starts,” says Janos Pasztor, executive director of the Carnegie Climate Governance Initiative, who wasn’t involved in the research. “If it's the clear, black-and-white—yes, it will happen, no, it will not happen—that's fairly easy. But if you say that it is likely that we've already passed the tipping point, that's a difficult concept. And it's very difficult for public communication.”

But, Pasztor says, these researchers have built a solid case that tipping points aren’t a far-off catastrophe—we’re already living them. “The evidence that it might actually be happening, that it might be true, is so high, that honestly this is just another very big reason why we need to get our act together and do everything that we could possibly do to fix the problem,” he says. “This is an article that just pulls together many, many good reasons why there is a real emergency, a real urgency here.”

Which is not to say all is lost. The faster we drastically cut emissions, the slower sea levels will rise. We must stop deforestation the world over, particularly in the Amazon. The long-term health of civilization depends on it.

And tipping points don’t have to be signs of trouble. “In the social realm, there are lots of tipping dynamics as well,” says Lenton. “Like you could argue that now we're seeing an accelerating uptake of renewable energy technology and electric vehicles.” People are waking up, and Greta Thunberg is leading a movement that’s growing more ferocious by the day.

As politicians and capitalists double down on the apocalypse, the more sensible among us are betting on change. Perhaps that’s the most critical tipping point of all.