The current record for the hottest year is likely to be broken again within the next five years, the Met Office says. As it stands, the hottest year on record was in 2016, when 1.16C of warming was recorded.
Analysis shows the five-year period from 2020 to 2024 is expected to be the hottest five years on record globally, as temperatures over the period are predicted to be between 1.15C and 1.46C above pre-industrial levels.
Global temperatures for each individual year are likely to exceed pre-industrial levels by between 1.06C and 1.62C.
The research reflects rising global temperatures, as the previous five years were the warmest such period on record, showing an average warming of 1.09C.
Scientists have warned of the dangers of allowing global warming of more than 1.5C, and countries have committed under the Paris climate deal to prevent reaching that threshold.
The Met Office forecast has estimated there is a less than one in 10 chance any single year in the next five years will reach 1.5C of warming.
The head of long-range prediction at the Met Office, Adam Shaife, said: "Barring a large volcanic eruption, these predictions show that we are rapidly approaching the point where we will see temporary excursions of global temperature above the 1.5C threshold."
But Professor Stephen Belcher, Met Office chief scientist, said reaching 1.5C of warming in an individual year would not breach the Paris agreement as the focus is on long-term temperature rises.
But he warned: "However, with our forecast showing a further warming trend, the window of opportunity continues to narrow."
Dr Doug Smith, a Met Office fellow and expert on decadal prediction, said the forecast suggests "continued warming, consistent with sustained high levels of greenhouse gases".
"Uncertainties exist within the forecast, but most regions are expected to be warmer and forecast patterns suggest enhanced warming over land, especially northern parts of Europe, Asia and North America - extending the ongoing trend," he added.
According to the forecast, temperatures in the north Atlantic are expected to rise, which could exacerbate warming over Europe.
Last year, the UK recorded its hottest ever temperature, reaching 38.7C (101.66F) in Cambridge Botanic Garden on 25 July.