The world will fail to meet the Paris agreement’s ambitious climate target

In its initial “assessment reports”—lengthy tomes of scientific knowledge on the climate, published every eight years or so—the Intergovernmental Panel on Climate Change conveyed what the future might look like through a range of “scenarios”. Each ended up with a different amount of global warming, based on different assumptions about policies, technologies, energy use and population size. But this approach proved hard for non-scientists to understand, let alone act upon.

By the time of the fifth report in 2013, however, it was clear the relationship between cumulative carbon-dioxide emissions and temperature rise was very linear. This meant all the complex nuance could be expressed as a simple “carbon budget”: if you want to limit warming to a specific level, there’s only so much CO₂ you can emit. For a 50% chance of limiting warming to 1.5°C above pre-industrial levels, the carbon budget was calculated to be 2,890bn tonnes. Human activity had already caused emissions of 2,390bn tonnes by 2019, so that left 500bn.

It now seems that 2026 will be one of the world’s last years in the black. The latest estimate is that, at the start of 2025, there were just 130bn tonnes of CO₂ left in the budget; and for a 67% chance of staying under the 1.5°C threshold, the remaining budget was just 80bn tonnes. So at the current rate of emissions, roughly 42bn tonnes a year, there is a 33% chance that the threshold will have been exceeded by the end of 2026, and warming of more than 1.5°C will be more likely than not by the end of 2027. The conclusion that humanity is heading for a post-1.5°C world seems inescapable.

Ideally, this should focus minds. Baked into the Paris agreement of 2015 was a tacit acknowledgment that countries could not (or would not) slash emissions fast enough to stop dangerous amounts of warming. So all practical trajectories for staying below 1.5°C or 2°C (the agreement’s looser, more realistic target) by the end of the century allowed for a period of “overshoot”, after which temperatures are brought back down.

The length and severity of this overshoot depends on how quickly emissions can be reduced to near-zero, and on the speed with which “negative emissions” technologies that suck up carbon dioxide, and thus compensate for the budgetary overshoot, can be deployed. (Such carbon-removal technologies exist, but only on a small scale and at eye-watering cost.)

So governments in 2026 and beyond face some hard choices. Once the 1.5°C threshold is passed, either reducing the temperature (via negative emissions), or stabilising it at a higher but not catastrophic level (ie, less than 2°C of warming), will still require dramatic emissions cuts. The future, as Homer Simpson exclaimed when a loan came due, has a habit of turning into the “lousy, stinking now”. ■