"There is a 98-percent 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 United Nations World Meteorological Organization said.
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 U.N. added.
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.
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.
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.
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," he said.
"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.
Britain's Met Office national weather service is the WMO's lead center on yearly to 10-yearly climate predictions.
"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.
