[Merrill]

The article in Nature published as a "Comment" is "Climate tipping points — too risky to bet against" - https://www.nature.com/articles/d41586-019-03595-0

For the ice sheet collapses, it takes 100s or 1000s of years for the effects to be realized. Others such as permafrost melting or Amazon forest disappearance are faster, but time scales are not given. For example -

>The Greenland ice sheet is melting at an accelerating rate3. It could add a further 7 m to sea level over thousands of years if it passes a particular threshold. Beyond that, as the elevation of the ice sheet lowers, it melts further, exposing the surface to ever-warmer air. Models suggest that the Greenland ice sheet could be doomed at 1.5 °C of warming3, which could happen as soon as 2030.

>Thus, we might already have committed future generations to living with sea-level rises of around 10 m over thousands of years3. But that timescale is still under our control. The rate of melting depends on the magnitude of warming above the tipping point. At 1.5 °C, it could take 10,000 years to unfold3; above 2 °C it could take less than 1,000 years6. Researchers need more observational data to establish whether ice sheets are reaching a tipping point, and require better models constrained by past and present data to resolve how soon and how fast the ice sheets could collapse.