Global average temperatures over land have plummeted by more than 1C since the middle of this year.
Revealed by NASA satellite measurements, it is the biggest and steepest fall on record, with temperatures returning to levels not seen since 1998.
The drop intemperatures has been caused by the end of El Niño – the warming of surface waters in a vast area of the Pacific Ocean, and has nothing to do with humans.
That El Niño has now been replaced by La Nina – when waters in the same Pacific region turn colder than normal.
The 2015-16 El Niño was probably the strongest since accurate measurements began, with the water up to 3C warmer than usual.