Another round of claims and counter-claims about climate is underway as natural variation takes its course. Talk of records often relates only to the satellite era.
Global average temperatures over land have plummeted by more than 1C since the middle of this year – their biggest and steepest fall on record, reports David Rose in The Mail on Sunday.
According to satellite data, the late 2016 temperatures are returning to the levels they were at after the 1998 El Niño. 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 Niño – 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 Niño, 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 Niños always have an immense impact on world weather, triggering higher than normal temperatures over huge swathes of the world. The 2015-16 El Niño 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It has now been replaced by a La Niña event – when the water in the same Pacific region turns colder than normal.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 Niño and La Niña. 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 Niño 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 Niño 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 Niño.
‘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.
Dr Schmidt also denied that there was any ‘pause’ or ‘hiatus’ in global warming between the 1998 and 2015 El Niños…However, both his own position, and his Nasa division, may be in jeopardy. US President-elect Donald Trump is an avowed climate change sceptic, who once claimed it was a hoax invented by China.
Last week, Mr Trump’s science adviser Bob Walker said he was likely to axe Nasa’s $1.9 billion (about £1.4 billion) climate research budget.
Other experts have also disputed Dr Schmidt’s claims. Professor Judith Curry, of the Georgia Institute of Technology, and president of the Climate Forecast Applications Network, said yesterday: ‘I disagree with Gavin. The record warm years of 2015 and 2016 were primarily caused by the super El Niño.’
The slowdown in warming was, she added, real, and all the evidence suggested that since 1998, the rate of global warming has been much slower than predicted by computer models – about 1C per century.
David Whitehouse, a scientist who works with Lord Lawson’s sceptic Global Warming Policy Foundation, said the massive fall in temperatures following the end of El Niño meant the warming hiatus or slowdown may be coming back.
‘According to the satellites, the late 2016 temperatures are returning to the levels they were at after the 1998 El Niño.
The data clearly shows El Niño for what it was – a short-term weather event,’ he said.