Next year will be one of the hottest on record and even warmer than 2022, the Met Office warned.
It will be the 10th year in a row that global temperatures have been at least 1C above pre-industrial levels, with a rise of between 1.08C and 1.32C forecast.
And experts said there is only a slim chance of a white Christmas on Sunday.
The UK recorded a 40.3C high in Coningsby, Lincs, last July as people hit resorts such as Blackpool in the summer.
It smashed the record of 38.7C set in Cambridge Botanic Garden in 2019.
The hottest year was 2016 when the El Nino climate pattern pushed up global temperatures. For three years the Pacific has had the opposite La Nina effect, leading to cooler weather.
The Met Office’s Dr Nick Dunstone said climate models predict this will end, adding: “This shift is likely to lead to global temperature in 2023 being warmer than 2022.”
It was also warned that UK heatwaves might regularly be above 40C even if global warming is limited to 1.5C.
Meanwhile, the chances of a white Christmas are low as the Met Office predicted showers for most parts.
Temperatures are forecast to be mild, although becoming colder across the far north, with snow at the end of the week.
The last widespread white Christmas in the UK was in 2010.
As Britain thaws from its coldest start to December in more than 100 years, South America will experience an extreme divide this week. Argentina and parts of Brazil will be at least 10C above or below the norm, respectively.
In Paraguay, the mercury will be up to 20C above average, with a 40C daytime maximum.
Parts of Central and Eastern Brazil are to receive up to 20cm of rain, a month’s worth, in a week.
