Next five years set to be hottest period ever: UN

It is near-certain that 2023-2027 will be the warmest five-year period ever recorded, the United Nations warned Wednesday as greenhouse gases and El Nino combine to send temperatures soaring.

Global temperatures are soon set to exceed the more ambitious target set out in the Paris climate accords, with a two-thirds chance that one of the next five years will do so, the UN's World Meteorological Organization said.

The hottest eight years ever recorded were all between 2015 and 2022 – but temperatures are forecast to increase further as climate change accelerates.

"There is a 98% likelihood that at least one of the next five years, and the five-year period as a whole, will be the warmest on record," the WMO said.

The 2015 Paris Agreement saw countries agree to cap global warming at "well below" two degrees Celsius above average levels measured between 1850 and 1900 – and 1.5C if possible.

The global mean temperature in 2022 was 1.15C above the 1850-1900 average.

The WMO said there was a 66 percent chance that annual global surface temperatures will exceed 1.5C above pre-industrial levels for at least one of the years 2023-2027, with a range of 1.1C to 1.8C forecasted for each of those five years.

'Uncharted territory'

While this does not mean that the world will permanently exceed the Paris benchmark, "WMO is sounding the alarm that we will breach the 1.5C level on a temporary basis with increasing frequency", said the agency's chief Petteri Taalas.

"A warming El Nino is expected to develop in the coming months and this will combine with human-induced climate change to push global temperatures into uncharted territory.

"This will have far-reaching repercussions for health, food security, water management and the environment. We need to be prepared."

El Nino is the large-scale warming of surface temperatures in the central and eastern equatorial Pacific Ocean. The weather phenomenon normally occurs every two to seven years.

Conditions oscillate between El Nino and its opposite La Nina, with neutral conditions in between.

The WMO said earlier this month that the chances of El Nino developing were 60 percent by the end of July and 80 percent by the end of September.

Typically, El Nino increases global temperatures in the year after it develops – which in this cycle would be 2024.

Despite the cooling influence of La Nina conditions over much of the past three years, the warmest eight years on record have all been from 2015 onwards, with 2016 the hottest.

Heat gets trapped in the atmosphere by so-called greenhouse gases, which are at a record high.

The three major greenhouses gases are carbon dioxide, methane and nitrous oxide.

Temperatures rising since 1960s

Global land and sea mean near-surface temperatures have increased since the 1960s.

The chances of temperatures temporarily exceeding 1.5C above the 1850-1990 average have risen steadily since 2015, a year when they were considered close to zero.

Britain's Met Office national weather service is the WMO's lead centre on yearly to 10-yearly climate predictions.

While there is a 66 percent chance that one year between 2023 and 2027 will exceed the 1.5C threshold, there is now a 32 percent chance that the entire five-year mean will do so, the Met Office said.

"Global mean temperatures are predicted to continue increasing, moving us away further and further away from the climate we are used to," said Met Office expert scientist Leon Hermanson.

Temperatures in 2023 are likely to be higher than the 1991-2020 average in almost all regions except for Alaska, South Africa, South Asia and parts of Australia, the WMO said.

Parts of the South Pacific Ocean are likely to be cooler than average.