New paper: Net zero could put global temperatures on a long, slow decline

Net zero – the point at which human-caused greenhouse gas emissions are balanced by removals – remains a goal for many companies and countries. Reaching that goal is far from guaranteed, and current policies still leave the world well off track.

But what would happen to global temperatures if we did get there?

In a new paper published this week in Nature Climate Change, Nathaniel Tarshish of the Harvard University Center for the Environment and his co-authors estimate that hitting the 2015 Paris Agreement target of net zero this century ushers in a global average temperature decline of at least 0.6°C (about 1.1°F) over the following centuries. The Paris target emerged from idealized experiments in which carbon dioxide is the only greenhouse gas – a world where net zero merely holds temperature steady. Real emissions, however, also include shorter-lived gases such as methane, whose warming impact fades after net zero. Hence, that plateau turns into a decline.  

The projection comes with caveats. It assumes that net zero is reached and sustained. Moreover, the decline it describes is a global average unfolding over centuries, not a rapid or uniform cooling. Even as temperatures fall, sea levels keep rising as the ocean takes up heat, and the ocean keeps acidifying as it takes up carbon dioxide. Still, the findings suggest that achieving net zero would do more than halt warming – it could begin to reverse it.