Global average temperature could temporarily cross a 1.5-degree Celsius (2.7 Fahrenheit) threshold next year, Britain's Met Office said on Friday, a milestone in climate history that could raise alarm at the COP28 summit being held in Dubai.

The Met Office said this year is almost certainly the warmest on record and 2024 could be even warmer.

The average global temperature for 2024 is forecast to be between 1.34C and 1.58C above the average for the pre-industrial period of 1850-1900, it said.

While hitting the 1.5C level in a single year does not mean the world will cross the long-term average warming threshold, the forecast is bound to add impetus to those calling for urgent action at the COP28 talks to curb climate-warming emissions.

"The forecast is in line with the ongoing global warming trend of 0.2C per decade, and is boosted by a significant El Niño event," said Nick Dunstone, who led the forecast at the Met Office.

"Hence, we expect two new global temperature record-breaking years in succession, and, for the first time, we are forecasting a reasonable chance of a year temporarily exceeding 1.5C...It's important to recognise that a temporary exceedance of 1.5C won't mean a breach of the Paris Agreement," he added.

The World Meterological Organization said last month that this year could reach warming of around 1.4C above pre-industrial records and extreme weather and record ice loss have provided a taste of what a long-term breach of the limit could be like.

In November, a team of scientists, including from NASA and Columbia University, said the world could cross the 1.5C threshold this decade.

Most emissions models under the United Nations Intergovernmental Panel on Climate Change (IPCC) show that the world could breach 1.5C during the 2030s.