First climate tipping point hit after coral reef diebacks, scientists warn

High ocean temperatures have cost 80% of the world's coral reefs their colour, warn scientists, while melting ice and rainforest loss push global warming to near-critical levels. Solutions are within reach but we must act now. Rebecca Speare-Cole reports

- 

Hardy Reef, Great Barrier Reef, Australia. Coral reefs - on which nearly a billion people and a quarter of all marine life depend - are already passing their thermal tipping point

RISING temperatures are pushing several of Earth's systems dangerously close to thresholds beyond which their demise accelerates and the global impacts become increasingly irreversible, according to a landmark report released on Monday.

The paper, led by Professor Tim Lenton from the University of Exeter and coauthored by more than 160 scientists in 23 countries, found that warm-water coral reefs - on which nearly a billion people and a quarter of all marine life depend - are already passing their thermal tipping point.

The scientists put this threshold at 1.2°C warming above pre-industrial levels but the world has now hit 1.4°C, meaning the impacts of passing the tipping point are under way.

In the last two years, more than 80% of the world's reefs have been affected by the worst bleaching event on record, with corals losing their colours and turning white because of stress largely caused by high ocean temperatures.

This means that unless the planet cools, these marine ecosystems will be lost globally, the scientists warned, before adding that small refuges may survive and must be protected.

The world is also rapidly approaching further catastrophic tipping points for ice melt, Amazon rainforest dieback and vital ocean currents as it nears the key milestone of 1.5°C warming above pre industrial levels.