As the curtain fell on the first year of the ‘tenties’, you may have found yourself perusing one of the dependable ‘year in review’ features. Any such selection of major events from 2010 would have no doubt included the Haiti earthquake, the Wikileaks revelations, and the protests – reported with redefined impartiality – against the UK Government’s own shock doctrine. Hopefully trivia items – perhaps including Christine O’Donnell, James Naughtie’s possible Freudian slip and blue-sky thinking from the Foreign Office – would have provided welcome respite. As memorable as they were however, for the world’s climate scientists, these stories are likely to have been eclipsed by early indications that 2010 was the hottest year on record.
Last year has now been confirmed as winner of joint pole position – tied with 2005 – in the global average temperature hall of fame, which spans the last 131 years. So what? Well, first, it is worth acknowledging that the revelation that 2010 was a record global sizzler of a year, might be greeted with surprise or even disbelief by many of the people who had their Christmas plans blighted by snow, and by ‘sceptical’ elements of the media. Does heavy UK snowfall mean global warming has stopped? Unfortunately not, and recent research suggests that unusually cold European winters could be caused both by lower sunspot activity and by a loss of sea-ice due to Arctic warming.
This colourful temperature map shows that, for much of the UK and Northern Europe, temperatures in December 2010 were at least 4°C colder than the 1951-1980 average for that month. However, because Europe is not the world, the European cold snap did not prevent the global average surface temperature for December from being almost half a degree warmer than the 1951-1980 average that provides context for NASA temperature measurements. Nor did it prevent large swathes of Canada and the Arctic from registering temperatures at least 4°C warmer than the historical average for December.
Readers may recall that the winter of 2009-10 was also unusually cold, however when compared with historical data, it seems that particularly cold winters have become the exception not the rule. According to data from NASA’s Goddard Institute for Space Studies, although the European winter of 2009-10 had a mean temperature of about 0.8°C below the 1951-1980 average, it was only one of four winters since that of 1986-87 that were colder than the average. The other 19 winters had above-average temperatures. Looking at European summer temperature anomalies is more concerning; only one summer in the same 23 year period had a below-average temperature; that of 1993.
To understand the significance – in terms of global warming – of yet another year being declared as the hottest on record, it is essential to consider the event in the context of long-term trends, a process far more informative than looking at temperature records broken in a given year. That being said, it is worth noting that 2010 received the dubious accolade of (joint) hottest year on record despite a strong episode of La Niña – the phenomenon which results in unusually cool sea-surface temperatures in the central and eastern tropical Pacific Ocean – in the second half of the year. Low levels of solar activity provided a further cooling effect. Go figure as they say in the US of A.
Let’s return to temperature trends considered over decades, which climate scientist James Hansen has described as “far more important than any particular year’s ranking”. The decade of 2001-2010 was the warmest on record, with an average global surface temperature of 0.56°C above the 20th century average, and with only one year (2008) that didn’t feature in the 10 warmest years ever recorded. According to data from the National Climatic Data Centre, December 2010 was the 310th consecutive month with a global temperature above the 20th century average. The graph below, which displays global surface temperatures from four temperature monitoring institutions, clearly indicates that temperatures have been above historical averages since the late 1970s, with a strong trend of increasing variation from the average.
Rising global surface (land and sea) temperatures – as depicted in a recent NASA animation – represent only two of ten established indicators of global warming. Unfortunately, the other 8 indicators also strongly suggest that our planet is warming. It seems clear that, if the trends in these indicators continue, 2010 is unlikely to hold its record as the warmest year for long.
