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2010 not 'warmest year ever' - close but no banana

By John McLean - posted Monday, 24 January 2011


The ABC headline screams "2010 the hottest year on record" and News Corp says "2010 warmest ever year says UN weather agency". Forgive me if I'm not excited. Not only did the World Meteorological Organization (WMO) actually headlined its media release, "2010 equals record for world's warmest year" but there are plenty of other reasons not to attach much significance to the claim.

There's a huge difference between "hottest year" and "equal warmest", especially when the difference between 2010 temperatures and 1998, 12 years earlier, was not statistically significant. The WMO states that two-hundredths of a degree separated 2010, 2005 and 1998, and that means that these high points are rather well spread over the 12 years, so much so that you would think the temperature was nearly flat.

The WMO media statement says that the data came from the UK's Hadley Centre and two other sources, but data directly from the Hadley Centre tells a different story. It shows the 2010 average temperature anomaly (the variation from the 1961-90 average) as being +0.468. It gives 2005 as +0.474 and 1998 as +0.529, leaving 1998 as still the peak temperature after 12 years and incidentally after the addition of plenty of carbon dioxide to the atmosphere. So much for claims of accelerated warming driven by a common greenhouse gas.

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The Hadley Centre data reveals something else that's important too. Temperatures for the first 3 months of 2002, not even 2005, were higher than in the corresponding months of 2010. For the remainder of the year, temperatures in 1998 were higher than 2010. So 2010 was just a combination of monthly data that happened to exceed the combinations of most other years.

Even if it was a record it would be none too impressive. Average global temperatures have only been calculated back to 1850 and on top of that, the data was obtained from less than 75% of the Earth's surface prior to 1959. A record over 60 years compared to the planet's lifetime of over 4 billion years sounds little to crow about.

Temperature records derived from Greenland ice cores suggest that the Little Ice Age, the 600 years to 1850, had almost the coldest temperatures and was the longest spell of virtually unchanged temperatures during the last ten thousand years. Despite the warming that has probably occurred since 1850 it's not even clear that temperatures today are above the average since the last Ice Age ended.

The WMO media statement specifically mentions warm conditions in Arctic Canada, Greenland, much of Africa, and parts of southern and western Asia. We might reasonably ask how the WMO knows this when almost all monitoring stations in northern Canada have been closed, Greenland's stations are around the coast - don't let map projections fool you into thinking either area is huge - and Africa is seriously deficient in monitoring stations.

Arctic sea ice is mentioned as being 10% lower than average in December and a record low in September, but again the records are very short and there's good evidence to suggest that even less ice was present in the 1930s. The minimum Arctic ice in 2010 was greater than the minimum in 2007 and the maximum was greater than that in 2005, 2006 and 2007. But should we really be very alarmed about this when the Earth seems to be still recovering from the Little Ice Age?

WMO Secretary-General Michel Jarraud said "The 2010 data confirm the Earth's significant long-term warming trend. The ten warmest years on record have all occurred since 1998." His statements are merely hype.

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Flat temperatures since 1998 don't confirm a long-term warming trend but they do suggest a plateauing. Similarly the five metres either side of the top of a hill usually contain the highest ten metres, so let's not get excited by the number of recent warm years.

I'd put Jarraud with the people who were happily to claim that a temperature hiatus of 15 years is too short to be meaningful and that cold days, weeks and months mean nothing, but conversely given warm weather across periods of matching length are quick to claim that it is evidence of man-made warming. According to them, natural forces cause cooler weather but never warmer weather.

Jarraud talks of a long-term warming trend but when temperatures have risen then plateaued and are now higher than near the start of the data, of course there will be a warming trend.

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About the Author

John McLean is climate data analyst based in Melbourne, Australia.

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