After record heat, could the Atlantic make Britain's weather even more extreme?

Watson's instinct is to keep the uncertainty visible. For him, caution is not complacency. It is a demand for precision.

Rahmstorf draws a different lesson from the same uncertainty. He sees a risk that is low enough to remain debated, but severe enough to demand action.

"We will not have certainty before it's too late," Rahmstorf says. "So we will have to act on our uncertainty."

The science does not offer a neat ending. It offers probabilities, warnings, caveats and arguments between experts who weigh the same clues differently.

But they agree on what is driving the risk.

The AMOC is being stressed by the warming of the planet. The more greenhouse gases humanity releases, the greater that stress becomes.