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2010 Temperature Update: Earth’s Second Warmest 12 Months on Record

23 October 2010

NOAA’s National Climatic Data Center (NCDC) have just updated their global surface temperature anomalies to include this September, so I thought it was time I updated my 2010 temperatures page, which was becoming rather neglected.

To recap, the year began with an unusually cold winter in northern land areas which had a disproportionate impact on public opinion. Yet while conservative commentators chattered about the cold winter, the global temperature soared. Globally January 2010 was a relatively warm month, and February 2010 was the warmest February on record in the Southern Hemisphere. March 2010 was not only the warmest March globally, but also the third warmest month of all time (seasonally adjusted), after February 1998 and January 2007. April 2010, May 2010, and June 2010 were the warmest April, May, and June respectively.

As predicted, during July 2010 the El Niño Southern Oscillation (ENSO) shifted to a La Niña phase, causing global temperatures to begin dropping. Nevertheless, it was still the second warmest July on record (after July 1998), at 0.66°C above the July average of 15.8°C. (Climatologists usually give temperatures as anomalies, in NCDC’s case anomalies relative to a 20th century average, because they are easier to compare than absolute temperatures.) In the Northern Hemisphere, it was the warmest July, with the warmest temperature anomalies in Europe, western Russia, eastern Asia, eastern North America, parts of Africa, and the Atlantic Ocean. There was a severe heat wave in Moscow, breaking the city’s nine-decade-old temperature record more than once. However, it was cooler than average in central Russia, southern South America, and the eastern Pacific Ocean (the latter obviously because of La Niña).

As La Niña strengthened, August 2010 tied for the third warmest August on record, at 0.58°C above the August average of 15.6°C. (August 1998 is the warmest, followed by August 2009.) Like July, this August was the warmest in the Northern Hemisphere (which this year had its warmest summer on record). Particularly warm temperatures were seen in eastern North America, most of Europe, northern Africa, parts of Asia, and the western Pacific. But there were again cool anomalies in central Russia and southern South America, as well as Australia and the UK, and of course the eastern Pacific.

September 2010 was the coolest month of the year to date (seasonally adjusted), at 0.49°C above the September average of 15.0°C. That makes it the tenth warmest September on record (warmest is September 2005). Although this is a cool month relative to the last decade, it is worth noting that it would have been a near-record-breaking anomaly as recent as 1989. The warmest anomalies were in most of North America, the North Atlantic Ocean, the Middle East, and northeastern Asia. Cooler anomalies were seen in Australia, central Russia, central Europe, and western Canada. La Niña conditions continued in the Pacific Ocean. The Southern Oscillation Index (SOI) was at its highest (most La Niña) value for any month since 1973, and the Australian Bureau of Meteorology (BoM) are currently predicting this La Niña will last until at least early 2011.

In my last temperature-related post three months ago, I mentioned the possibility of a new record being set for the 12-month mean global temperature in the NCDC analysis (which had already happened in NASA’s GISS analysis). So what happened? It turns out the 12 months ending in July 2010 registered an anomaly of 0.64°C, the second warmest of the 1,558 such periods on record. The 12 months ending in August 2010 came third at 0.63°C. The former fell only a hundredth of a degree short of the record-holder (September 1997 to August 1998, which occurred during a super El Niño) — well within the error bars, essentially a tie. You get the idea: those 12 months were pretty warm.

The year-to-date (which now means January-September) is no longer the outright warmest but is tied with the corresponding period in 1998. However, it has become clear that this year will not be, as I have speculated, a repeat of 2007 (which like 2010 had a record-warm beginning during an El Niño, but unlike 2010 cooled rapidly with the onset of La Niña). Comparing the global temperature anomalies for the first three-quarters of each year, 0.65°C for 2010 versus 0.57°C for 2007, we can now see that this year will be considerably warmer.

So all the indications are that current global temperatures are hot, hot, hot — but of most interest to the public is the warmest calendar year. Currently the record-holder is 2005, at 0.62°C above the annual average of 13.9°C, followed by 1998 (0.60°C). The years 2001-2009 are all among the top ten. Where 2010 fits in will depend on whether global temperature continues to drop or flattens out, but in any case it looks set to make the top three. Based on my own calculations, if the remaining three months of the year average about 0.53°C, then 2010 will set a new calendar year record in the NCDC analysis. If they average between 0.46°C and 0.53°C, 2010 will be second warmest; if between 0.39°C and 0.46°C, it will be third warmest. (For comparison, the final quarter of 2007 averaged 0.47°C; the end of 1998 0.44°C.)

NASA’s Goddard Institute for Space Studies (GISS) seem to be reasoning along the same lines. According to their discussion of current global temperatures:

The last four months of 2005 […] were unusually warm, so it is not possible to say yet whether 2005 or 2010 will be the warmest calendar year in the GISS analysis. It is likely that the 2005 and 2010 calendar year means will turn out to be sufficiently close that it will be difficult to say which year was warmer, and results of our analysis may differ from those of other groups.

Furthermore, GISS argue that 2012 could set a new record global temperature higher than 2010:

Projections of trends over the next few years are possible based on the following considerations:

(1) the planet is out of energy balance by at least several tenths of one W/m2 due to the rapid increase of greenhouse gases during the past decades, as confirmed by measurements of changing ocean heat content,

(2) inertia of energy systems that assures continuing growth of atmospheric CO2 by about 2 ppm per year for the next few years,

(3) expectation that the solar irradiance will climb out of the recent long-lasting solar minimum […]

(4) model projections suggesting that the current La Niña may bottom out near the end of 2010.

Given the dominant effect of El Niño-La Niña on short-term temperature change and the usual lag of a few months between the Niño index and its effect on global temperature, it is unlikely that 2011 will reach a new global record temperature.

In contrast, it is likely that 2012 will reach a record high global temperature. The principal caveat is that the duration of the current La Niña could stretch an extra year…

Whatever the exact outcome is, a record or near-record high global temperature is impressive when you consider that we are presently coming out of the lowest solar minimum in a century. Is there any chance that the Sun could save us from global warming? Although NASA are also predicting that the new solar cycle will be much quieter than usual, the GISS 2008 annual summation stated that even assuming

that the solar irradiance does not recover […] the negative forcing, relative to the mean solar irradiance is equivalent to seven years of CO2 increase at current growth rates. So do not look for a new “Little Ice Age” in any case.

Taking a broader view than 2010 temperatures, there is no sign that the long-term warming trend has changed. The 2000s are the warmest decade on record, followed by the 1990s and 1980s. Look at the anomaly map for any month in the last decade and you’ll see much more warmth than cold. In the NCDC analysis, the last month with a temperature below average was February 1985. The 25-year trend remains at around 0.17°C per decade. However you slice and dice it, there is no indication that global warming has been cancelled.

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