Average annual global temperatures could soon cross the 1.5-degree Celsius (2.7 Fahrenheit) mark for the first time, the UN weather agency said on Thursday.

There is a one-in-five chance that the world will experience average temperatures 1.5 C higher than the pre-industrial average in at least one year between now and 2024, the Geneva-based World Meteorological Organization said. It said the chance that this threshold would be exceeded in a single month in those years was 70%.

The average temperatures around the world are very likely to be at least 1 degree above the 1850-1900 average in each of the five years, according to the WMO.

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Targeted limit

The 1.5 C mark is the ideal cap for global heating targeted by countries in the Paris Agreement of December 2015to minimize the effects ofclimate change.

Even if cooler years followed one in which the threshold was surpassed, experts say, exceeding it would still be an indication that current efforts to reduce global heating are not working.

The forecasts are contained in an annual climate outlook put together under the leadership of the UK's Met Office.

Read more: Nigeria's Bayo Akomolafe: We aren't 'in control' of climate crisis  

'Sustained and coordinated climate action' needed

WMO chief Petteri Taalas said the forecasts highlighted the "enormous challenges" faced by countries who signed the accord.

He said that although the computer models used for the forecasts did not factor in the impact the coronavirus pandemic might have on emissions of greenhouse gases, the pandemic-induced slowdown was not likely to lead to any significant reduction of CO2 atmospheric concentrations.

"The industrial and economic slowdown from COVID-19 is not a substitute for sustained and coordinated climate action," Taalas said.