It is the latest red flag in a year already hit by climate extremes and rising greenhouse gas emissions, spurring fresh calls for more rapid action to limit global warming.

"The global average temperature for the last 12 months (June 2023-May 2024) is the highest on record... and 1.63 degrees Celsius above the 1850-1900 pre-industrial average", EU monitor Copernicus said, referring to the period before human-caused greenhouse gas emissions began warming the planet.

Copernicus made the announcement in a coordinated publication with the World Meteorological Organisation (WMO) and a speech by UN secretary-general Antonio Guterres in New York, in which he called for a ban on advertising of fossil fuels.

In May, the global average temperature was 1.52C above the pre-industrial average.

May was also the 11th consecutive month since July 2023 at or above 1.5C compared with the pre-industrial era, Copernicus said.

This doesn't mean the 1.5C warming limit agreed by world leaders in Paris in 2015 has been breached -- that is measured in decades, not individual years.

The El Nino natural weather phenomenon, which increases global temperatures and has accentuated the effects of global warming for the past year, "is showing signs of ending", the WMO said Monday.

The opposing cycle, La Nina, which lowers global temperatures, is expected to begin later this year, according to the WMO.

But scientists have warned the cooling effect could be miniscule compared to the effect human-caused global warming, which is already responsible for raising global temperatures by at least 1.2C since the end of the 19th century.