The world warmed more rapidly than previously thought over the past decade, according to a Met Office report published today, which finds the evidence for man-made climate change has grown even stronger over the last year.
The report comes ahead of the first major UN climate negotiations since the Copenhagen summit last December, which begin on Monday in Cancún, Mexico, and as scientists predict that 2010 could be the hottest year on record.
The Met Office report includes a new study which shows that sea surface temperatures were higher than initially thought because of a change in the way the temperatures were measured after 2000. The new analysis significantly increases the warming scientists think was seen globally over the past decade.
The work is significant because the rate of global warming from 2000-2009 is lower than the 0.16C per decade trend seen since the late 1970s, a fact climate scientists have been keen to explain. Including the new sea surface temperatures, which push up global temperatures by 0.03C, the warming rate for the past 10 years is estimated at 0.08-0.16C. The new analysis of sea surface temperatures adjusts underestimates which arose from the change from predominantly ship-based temperature measurements before 2000 to mostly buoy-based measurements afterwards.
The Met Office’s Dr Vicky Pope added that there were good explanations why warming had slowed over the past 10 years. Natural variation alone in the chaotic climate system would produce such a slowing every eight decades, even with the long-term warming trend seen. Other factors include changes in solar activity, the increased water vapour that can be held by warmer air and soot and other particles produced by fossil fuel and wood burning in Asia.
Dr Pope said there was no doubt that the past decade was on average hotter than the 1990s. On the apparent contradiction between the faster loss of sea ice and the less rapid rise in temperatures this decade, she said: “This is entirely consistent with our understanding of how the climate behaves and with our model projections.”
She noted that nine different indicators of climate change, from temperature to sea level to humidity to snow cover, all showed a warming trend that can only be explained by the increase in greenhouse gas emissions from human activities. Multiple datasets are available for each of these indicators, she said.
The global average temperature for 2010 could be the highest since records began in the 1850s, Pope said. Of the three major independent records of global temperature, one puts 2010 on track to exceed the previous peaks in 1998 and 2005, while the other two appear set to run those records very close. The records, from the Met Office, NOAA and Nasa, have small differences due to how they deal with gaps in data from remote parts of the world, in particular the Arctic where warming is faster than at lower latitudes.
Even with a possible cool end to the year, 2010 is expected to be no lower than third in record temperatures. “I would not be surprised if most or all groups found that 2010 was tied for the warmest year,” said Nasa’s Dr James Hansen. The 2010 temperature will be revealed by the World Meteorological Organisation, which includes all the records in its estimate, on Thursday 2 December at the UN talks in Mexico.
