Surpassing 1.5°C of warming can be undone at a later date – using tech, land and resources that don’t exist.

De facto, what they said was this: staying below a temperature limit is the same as first crossing it and then, a few decades hence, using methods of removing carbon from the atmosphere to dial temperatures back down again.

From some corners of the scientific literature came the assertion that this was nothing more than fantasy. A new study published in Nature has now confirmed this critique. It found that humanity’s ability to restore Earth’s temperature below 1.5°C of warming, after overshooting it, cannot be guaranteed. Many impacts of climate change are essentially irreversible. Those that are might take decades to undo, well beyond the relevant horizon for climate politics. For policy makers of the future, it matters little that temperatures might eventually fall back again; the impacts they will need to plan for are those of the overshoot period itself.