Britain's Climatic Research Unit (CRU), which for years maintained that 1998 was the hottest year, has published new data showing warmer years since, further undermining a sceptic view of stalled global warming.
The findings could helpfully move the focus from whether the world is warming due to human activities – it almost certainly is – to more pressing research areas, especially about the scale and urgency of human impacts.
After adding new data, the CRU team working alongside Britain's Met Office Hadley Centre said on Monday that the hottest two years in a 150-year data record were 2005 and 2010 – previously they had said the record was 1998.
None of these findings are statistically significant given the temperature differences between the three years were and remain far smaller than the uncertainties in temperature readings.
Yet contrarian scientists and others who doubt the mainstream view that humankind is warming the world have used the notion of a post-1998 plateau to urge policymakers to ease targets on renewable energy and cutting carbon.
Some 16 scientists (some retired and not specialist in the climate field) in an opinion article published in the Wall Street Journal in January used it at the core of their "no compelling scientific argument for drastic action".
"Perhaps the most inconvenient fact is the lack of global warming for well over 10 years now," they wrote.
Sceptics have pointed to a levelling off of temperatures since a very strong, natural (El Nino) weather pattern produced a record warm year worldwide in 1998.
The article drew a riposte from scientists pointing out that the last decade was the warmest on record. Experts have long urged not to focus on individual years but periods of a decade or more when trying to show trends.
CRU drew fire during the 2009 ‘Climategate’ scandal which derailed UN talks in Copenhagen and tripped up efforts at a US climate bill.
It was sparked after leaked emails showed CRU scientists, led by Phil Jones, sniping at rivals. The CRU was criticised in subsequent public enquiries for not sharing data but exonerated of any manipulation.
Nevertheless, it was the most cautious major climate research centre, in cooperation with the Met Office Hadley Centre, holding the view that 1998 was the hottest year in an observation record dating back to around 1850.
Its peers are the US-based National Oceanic and Atmospheric Administration, and NASA's Goddard Institute for Space Studies.
Both had already found that 2005 and 2010 were warmer than 1998. They used an approach which gave more weight to the Arctic, where temperatures have risen faster than the rest of the world, but where there are also fewer observations.
They expanded Arctic coverage by statistically inferring warming in areas without weather stations, using neighbouring observations.
Now the CRU-Hadley Centre team have included more than 400 extra actual Arctic observations from Russia and Canada, as these countries have made these available, leading to the change in the annual ranking, which is based on fractions of a degree.
All three research centres estimate global warming of about 0.8 degrees Celsius since 1900, and nearly 0.2 degrees per decade since 1979.
This story was originally published by Reuters. Reproduced with permission.