Warm-water reefs reach tipping point, signaling irreversible change

A major international scientific assessment published this week concludes that warm-water coral reefs have passed their thermal tipping point, marking the first identified climate tipping point and signaling a new phase of climate-driven, hard-to-reverse ecosystem change. The Global Tipping Points report, compiled by 160 scientists from 23 countries and led by researchers at the University of Exeter, warns that rising ocean temperatures together with acidification, overfishing and pollution have driven widespread bleaching and mortality that put many reef systems at risk of large-scale loss unless global temperatures are brought back toward preindustrial levels.

The authors define a tipping point as a threshold beyond which changes become self-perpetuating and difficult to reverse. The report identifies a central estimate of about 1.2 degrees Celsius of global warming as the thermal threshold for extensive warm-water reef dieback. Global average temperatures are currently around 1.3 to 1.4 degrees Celsius above preindustrial levels, and the World Meteorological Organization projects the world could cross 1.5 degrees Celsius within the next five years. Those conditions make...