Sea temperatures also broke April and May records.
Global average sea surface temperatures hit 21C in late March and have remained at record levels for the time of year throughout April and May.
Australia's weather agency warned that Pacific and Indian ocean sea temperatures could be 3C warmer than normal by October.
Though this year's high sea temperatures are caused by a "perfect combination" of circumstances, the ecological impact could endure, she said.
The Worldwide Fund for Nature, however, warned of a "worrying lack of momentum" during climate talks in Bonn this month, with little progress made on key issues like fossil fuels and finance ahead of November's COP28 climate talks in Dubai.
Persons:
Kerry, Sarah Perkins, Kirkpatrick, Piers Forster, El Nino, Annalisa Bracco, Li Shuo, John Kerry, Li, David Stanway, Ali Withers, Gloria Dickie, Jamie Freed
Organizations:
EU, Australia's University of New, U.S ., World Meteorological Organization, El Nino, University of Leeds, Georgia Institute of Technology, DUBAI, The, Nature, Thomson
Locations:
Beijing, SINGAPORE, Bonn, Australia's University of New South Wales, United States, North America, Canada, U.S . East Coast, India, Spain, Iran, Vietnam, Paris, 1.5C, California, Africa, November's, Dubai, China, Copenhagen, London