These points are defined as a reinforcing feedback in a climate system that is so strong it becomes self-propelling at a certain threshold -- meaning even if warming stopped, an ice sheet, ocean or rainforest would keep changing to a new state.

While early assessments said these would be reached in the range of 3-5C of warming, advances in climate observations, modeling and paleoclimate reconstructions of periods of warming in the deep past have found the thresholds much lower.

The new paper is a synthesis of more than 200 studies to produce new estimates for when common tipping points might happen.

It identifies nine global "core" tipping elements contributing substantially to planetary system functioning, and seven regional tipping points, which contribute substantially to human welfare, for a total of 16.

Five of the 16 may be triggered at today's temperatures: the collapse of the Greenland and West Antarctic ice sheets; widespread abrupt permafrost thaw; collapse of convection in the Labrador Sea; and massive die-off of tropical coral reefs.

Four of these move from "possible" events to "likely" at 1.5C global warming, with five more becoming possible around this level of heating.

10 meters of sea rise

Passing the tipping points for the Greenland and West Antarctic ice sheets is "making a commitment eventually to an extra 10 meters of global sea level," said Lenton, though this particular change may take hundreds of years.

Coral reefs are already experiencing die-offs due to warming-induced bleaching, but at current temperatures they are also able to partly recover.

At a particular level of heating, recoveries would no longer be possible, devastating equatorial coral reefs and the 500 million people globally who depend on them.

The Labrador Sea convection is responsible for warming Europe and changes could result in much more severe winters, comparable to the "Little Ice Age" from the early 14th century through the mid-19th century.

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