|Land temperatures, December 2010|
BBC Environment correspondent
US researchers say new evidence casts doubt on the idea that global warming has "slowed" in recent years.
A US government laboratory says the much talked about "pause" is an illusion caused by inaccurate data.
Updated observations show temperatures did not plateau, say National Oceanographic and Atmospheric Administration (Noaa) scientists.
The warming rate over the past 15 years is "virtually identical" to the last century, they report in Science.
Dr Thomas Karl of NOAA, who led the new analysis, said: "We would hope that it would inform the general public that the temperature today really is continuing to warm."
One begins to suspect that the 'hiatus' or pause in global warming was a problem for climate change scientists. It shouldn't be; a pause should have been expected, perhaps even a brief drop in the earth's temperature. This is the kind of thing that makes me suspicious.
The idea of a global warming "hiatus" arose from questions over why the trend of warming temperatures appeared to be stalling recently compared to the later part of the 20th Century.
|There are still gaps in data, such as in the Arctic|
The new analysis corrects for ocean observations made using different methods as well as including new data on surface temperatures.
Dr Peter Stott of the Met Office Hadley Centre said the results "still show the warming trend over the past 15 years has been slower than previous 15 year periods" and "global temperatures have not increased smoothly".
Curious! Dr Stott is not quoting the NOAA report but rather is referring to IPCC data. As you will see, immediately below, NOAA has decided that the rate of global warming has increased over the past 15 years. Has Stott rejected NOAA's findings? Unfortunately, the BBC reporter did not seem to pick up on the discrepancy.
Dr Stott's comment is quite reasonable - one would not expect global warming to be smooth and consistent. There are so many factors that influence global temperatures that a smooth trend line can't be possible. NOAAs smoothing of that trend-line by the addition of 'new' data and the rejection of some old data, is therefore suspect and should be scrutinized very thoroughly, if not completely dismissed.
"This means natural variability in the climate system or other external factors has still had an influence and it's important we continue research to fully understand all the processes at work," he said.
|"NOAA - how long can you tread water?"|
This compares with an average of 0.12 per decade between 1951 and 2012.
The new analysis suggests a figure of 0.116 per decade for 2000-2014, compared with 0.113 for 1950-1999. An actual, though slight, increase in the warming trend! Who saw that coming?
"The IPCC's statement of two years ago - that the global surface temperature 'has shown a much smaller increasing linear trend over the past 15 years than over the past 30 to 60 years' - is no longer valid," said Dr Karl, the director of Noaa's National Climatic Data Center.