1Climate scientists increasingly warn that the Earth system contains thresholds which, once crossed, may prove impossible to reverse.
2These tipping points include the collapse of great ice sheets, the death of coral reefs, and the thawing of frozen northern soils.
3The Greenland ice sheet alone holds enough frozen water to raise global sea levels by several metres over the coming centuries.
4Beneath the Arctic tundra, vast stores of carbon lie locked in permafrost that has remained solid for thousands of years.
5As the frozen ground warms, this carbon escapes as methane, a gas far more potent than carbon dioxide.
6The released methane then accelerates the warming, which in turn thaws even more permafrost in a dangerous self-reinforcing loop.
7Researchers stress that such loops operate largely beyond human control once they have gathered sufficient momentum of their own.
8Nevertheless, the same science offers hope, because rapid and deep emission cuts can still keep most thresholds beyond reach.
9Every fraction of a degree of warming we prevent meaningfully reduces the probability of triggering these irreversible planetary changes.
10The window for effective action is undeniably narrow, yet most experts agree that it has not yet closed entirely.
11What we do in this decade will shape the climate of the planet for countless generations to come.