The world isn’t currently on track to ramp down emissions fast enough to keep 1.5 degrees of warming from happening. That means we could be headed for an overshoot scenario: a future where the world blows by warming targets, but through emission reductions and removing carbon from the atmosphere, temperatures eventually get back within the safe zone.

Even if temperatures are brought back in line, the impacts of a hotter planet in the interim won’t be reversible. Species that go extinct won’t come back. Coral reefs that die won’t regenerate. Rising seas won’t recede into their prior ice formations. All of the human suffering from living in an overheated world with more extreme weather fluctuations won’t be magically undone. And once changes to natural systems start -- like the melting permafrost already underway -- eventually lowering temperatures won't necessarily stop them.

Why This Matters

Understanding the risks of an overshoot scenario demonstrates the imperative to take action now. The world is currently on track to hit 3 degrees Celsius of warming. Last month’s IPCC report encouraged global leaders to embrace "transformational” change to keep the world from going beyond the limits of adaptation. Even if that number eventually dropped back down below 1.5 degrees, the damage and irreversible changes would already be underway.

"Humans can control human actions, but humans cannot control the biosphere’s responses to climate change,” Camille Parmesan, an ecologist and professor at the French National Centre for Scientific Research, told Grist. And we’re witnessing responses that are going to make it harder and harder and harder for humans to get global warming down.”

Overshoot Scenarios Are Regular in Research

While the term "overshoot” hasn’t made its way into many headlines yet, it’s common in scientific papers and in climate policy discussions. A recent article in Nature Climate Change about meeting emission targets without overshoot begins with criticism of the current scenarios because "they feature strategies with pronounced overshoot of the global temperature goal, requiring a long-term repair phase to draw temperatures down again through net-negative emissions.”