Global average temperatures over land have plummeted by more than 1C since the middle of this year – their biggest and steepest fall on record. According to satellite data, the late 2016 temperatures are returning to the levels they were at after the 1998 El Nino.
The news comes amid mounting evidence that the recent run of world record high temperatures is about to end.
The fall, revealed by Nasa satellite measurements of the lower atmosphere, has been caused by the end of El Nino – the warming of surface waters in a vast area of the Pacific west of Central America.
Some scientists, including Dr Gavin Schmidt, head of Nasa’s climate division, have claimed that the recent highs were mainly the result of long-term global warming.
Others have argued that the records were caused by El Nino, a complex natural phenomenon that takes place every few years, and has nothing to do with greenhouse gas emissions by humans.
The new fall in temperatures suggests they were right.
Big El Ninos always have an immense impact on world weather, triggering higher than normal temperatures over huge swathes of the world. The 2015-16 El Nino was probably the strongest since accurate measurements began, with the water up to 3C warmer than usual
It has now been replaced by a La Nina event – when the water in the same Pacific region turns colder than normal.
This also has worldwide impacts, driving temperatures down rather than up.
The satellite measurements over land respond quickly to El Nino and La Nina. Temperatures over the sea are also falling, but not as fast, because the sea retains heat for longer.
This means it is possible that by some yardsticks, 2016 will be declared as hot as 2015 or even slightly hotter – because El Nino did not vanish until the middle of the year.
But it is almost certain that next year, large falls will also be measured over the oceans, and by weather station thermometers on the surface of the planet – exactly as happened after the end of the last very strong El Nino in 1998. If so, some experts will be forced to eat their words.
Last year, Dr Schmidt said 2015 would have been a record hot year even without El Nino.
‘The reason why this is such a warm record year is because of the long-term underlying trend, the cumulative effect of the long-term warming trend of our Earth,’ he said. This was ‘mainly caused’ by the emission of greenhouse gases by humans.