The year 2018 is likely to have been the fourth warmest year on record, a scientific group said yesterday - and joins a quartet of extra-hot years since 2015 that suggest a leap upward in warmth that the Earth may never return from in our lifetimes.
The warmest year on record for the Earth's land and oceans was 2016 - by a long shot, thanks to a very strong El Nino event. That's followed by 2017, 2015, and now 2018, said Zeke Hausfather, a research scientist with Berkeley Earth, which released the findings.
Hausfather said: "2018 is consistent with the long term warming trend. It's significantly warmer than any of the years before 2015. There's still this big bump up after 2014, and 2015, 2016, 2017, and 2018 are all in a class of their own."
While expert groups have sometimes divided on such annual temperature rankings - and not all assessments are yet in - Berkeley Earth's findings appear unlikely to be disputed.
The Copernicus Climate Change Service, a European Union body, has also proclaimed 2018 the fourth warmest year on record.
And Kevin Cowtan, a researcher at the University of York who also keeps an influential temperature dataset, agreed with the ranking, though he noted by email that he is only able to track data through to November of last year due to the US government shutdown, leaving his assessment one month short at present.
"The 11 hottest years on record have all occurred since 2005," he said.
Amid the government shutdown the two top US keepers of temperature records - Nasa and NOAA - have not yet released their findings.
Hausfather said a co-ordinated release had been planned for January 17 with his organisation and the US government agencies - before the shutdown, that is. Once that happened, he said, Berkeley Earth decided to go ahead and release its own numbers.
Twenty-nine countries had their hottest years on record, Berkeley Earth found, including European countries like France and Germany but also Middle Eastern nations like Oman and the United Arab Emirates.
Notably, Antarctica also saw its warmest year on record, the group found.
The year yet again featured an odd cold anomaly in the seas to the southeast of Greenland, which some scientists think may represent a slowing down of the "overturning" ocean circulation in the Atlantic. Clearly, this region is bucking the overall warming trend.
From a political and policy perspective, the last several extra warm years are highly significant. That's because they appear to be at or above a 1C increase above so-called "preindustrial" temperatures, or temperatures from the later part of the 19th century.
In Berkeley Earth's dataset, the past five years are all above 1C; in two other datasets the past four years are expected to be above that threshold, according to data provided by Hausfather. In the National Oceanic and Atmospheric Administration dataset, 2018 is trending slightly under it.
Either way, this matters because scientists have outlined increasingly dire consequences as soon as the Earth reaches 1.5C or 2C, temperature targets that are both flagged in the 2015 Paris climate agreement.
The arrival of 1.5C could happen in under two decades. In fact, it has in effect already happened for many land areas, since land surfaces are warming quicker than the ocean at this point. But the oceans are warming too - they may have been the warmest on record in 2018.
Berkeley Earth projects that this year may well be warmer than every year so far except for 2016 - and thus will once again be above 1C.
"It's unlikely at this point that we'll have a situation where temperatures dip back below that, at least for the globally complete datasets," said Hausfather. He termed the current temperature range - which has seen more extreme heat events, major coral bleaching and death around the world, and alarming wildfires, among other climate-linked occurrences - a "new normal".