Humanity’s greatest risk – Triggering climate tipping points.
Humanity is increasing climate-heating gases at the fastest rate in the geological record, the whole history of the planet as far as we can understand it. The result is the most rapid heating we can detect. What took centuries now occurs in decades. The growing risk is that we will set off a cascade of tipping points that drive the climate into chaos, potentially realizing something like those Exeter scenarios. This graphic depicts them:

A master tipping point is the AMOC, the Atlantic Meridional Overturning Circulation, the place in the North Atlantic where warm currents coming from the south sink to the depths, weighed down by their salt content. That opens space drawing the current north. But meltwater from a warming Greenland has been diluting the saltiness and slowing the sinking with knock-on effects reaching back into the entire oceanic circulation. A study published in April found a 90% probability the AMOC will slow 51% by 2100, putting it on a path to eventual shutdown. Impacts could extend to Antarctica and the Pacific. African and Indian monsoons could weaken. This might be happening already with slowing. Shutdown threatens to dry out Amazonia and the African Sahel. It would cool and dry Europe, elevate U.S. east coast sea levels, and pile up heat in southern latitudes.
“I have personally researched this for 35 years,” says Stefan Rahmstorf, one of the world’s leading scientific experts on the AMOC. “For the first 30 years we considered this a low likelihood event. I would have said a 5 percent chance of occurring. It’s more like 50/50 now. I would even say more likely than not.”
A recent study from Utrecht University offers perhaps the first ray of daylight in the otherwise grim picture. It showed that the AMOC could collapse at as little as 2° C heating. But if the rate of heating is slowed, the current might remain stable even at 5° C heating.
The Utrecht study brings home the most important message of this piece. Everything depends on the rate of change. Given time to adjust, the Atlantic Ocean can potentially fend off AMOC collapse even under extreme heating. This message applies across the range of climate impacts. We must slow the rate of climate heating as much as possible to avert the worst impacts. That is most important project humanity now faces. It is why, contemplating tipping points dangers some years ago, I revised my climate mission to leaving a planet with which our kids can cope.
Unfortunately, the world is still tracking at a higher rate, heating around 0.3°C per decade. We are bumping up against the 1.5°C target set by the 2015 Paris Climate Summit. A new report from the United Nations Environment Program admits we have blown the 1.5°C goal. The best we can expect is to peak at 1.8-2° C. The report holds out hope that humanity can bring temperatures back down with strong action.
“There are no good outcomes if we remain above 1.5°C. Across the globe, extreme heatwaves are already proving that climate impacts will strike faster, hit harder, and last longer, costing more lives and causing deeper disruption,” said Inger Andersen, executive director of UNEP. “Now is the time we must double down on climate action. We can and must get on the right path by cutting greenhouse gas emissions, strengthening resilience and adaptation, and ensuring exceedance of 1.5°C is as small and short as possible.”

But overshooting 1.5° escalates risks of setting off tipping points, as this graphic from the Global Tipping Points 2025 report shows. The range between 1.5-2°C is crucial. Nearing the low end danger signs are already showing. Coral reefs have already tipped over. Glacier loss from West Antarctica is increasing. The North Atlantic subpolar gyre is destabilizing for the same reasons as the AMOC and could collapse faster. Risk to mountain glaciers gained a bold underscore in Nepal. The Amazon rainforest may be tipping from carbon soaker to emitter. Earth is crossing critical thresholds beyond which dangers radically increase. That’s one reason 1.5°C was targeted in the first place.
Science Daily’s report on the Utrecht study offers a caution on overshoot strategies that might well apply to the range of tipping points. “Much of current climate policy, including the Paris Agreement, focuses on limiting the eventual peak in global temperature. Some strategies involve so-called overshoot pathways . . . The new findings suggest that the path taken toward a given temperature may matter alongside the temperature itself. The faster global warming occurs, the less time the Atlantic Ocean has to adjust, potentially increasing the vulnerability of one of the planet’s most important circulation systems.”
I know people who have made seminal contributions to the cause of the climate and the Earth who have looked at this picture and thrown up their hands in despair. But I’m not there yet. I know that every tenth of a degree could spell the difference between worst-case scenarios and more survivable outcomes. I helped bring a child into the world 30 years ago to the day I am writing this. So I have a direct investment in future generations. But even if I didn’t I could not accept even the remote possibility of billions dying if I could possibly do anything about it.