Ocean heat hit a record high in 2018, the United Nations said Thursday, raising urgent new concerns about the threat global warming is posing to marine life.
In its latest State of the Climate overview, the World Meteorological Organization (WMO) reaffirmed that the last four years had been the hottest on record -- figures previously announced in provisional drafts of the flagship report.
But the final version of the report highlighted worrying developments in other climate indicators beyond surface temperature.
"2018 saw new records for ocean heat content in the upper 700 metres," a WMO statement said. Last year also saw new heat records for the ocean's upper 2,000 metres.
UN Secretary-General Antonio Guterres described the latest findings as "another strong wake-up call" for governments, cities and businesses to take action.
The United Nations is hosting a major summit on September 23 that is billed as a last-chance opportunity for leaders to tackle climate change, which Guterres has described as the defining issue of our time.
The UN chief has urged world leaders to come to the summit with concrete plans, instead of speeches, to reduce greenhouse gas emissions by 45 percent over the next decade and to net zero by 2050.
About 93 percent of excess heat -- trapped around the Earth by greenhouse gases that come from the burning of fossil fuels -- accumulates in the world's oceans.