The Temperature Of 2012
2012 started off remarkably coolly due to a lingering La Nina. According to the global temperature dataset Hadcrut3 January was the 15th warmest January on record, February the 22nd, and March the 15th warmest. The same unusual coolness is also seen in the NasaGiss database which has January the 17th warmest on record, February the 15th and March the 15th warmest.
In both datasets the Northern Hemisphere Spring was considerably warmer, though not a record in these combined land and ocean datasets. In Hadcrut3 April was the 5th warmest April, May the 4th warmest and June the 5th warmest. In NasaGiss April was the 5th warmest April on record, May the 2nd and June the 4th. July data is so far only available from NasaGiss and it was the 11th warmest July on record.
Even though the transition to El Nino conditions began a few months ago the elevated temperatures it will bring will probably not be enough to put 2012 among the record warm years of 2005, 2010 and 1998. Noaa has released a graph showing its estimates of the global temperature this year and it is obvious that the remainder of the year is highly unlikely to make 2012 a record breaker.
The land only data is interesting. Currently only the analysis from Noaa is available. Like the global datasets mentioned previously the first three months of the year were cool – 28th,37th and 18th warmest months for January – March. But May and June were records (due to the Northern Hemisphere) and July the 4th warmest July on Noaa’s database.
Noise In The System
Month to month variations are of course the noise in the system. We live in the warmest decade of the instrumental record but also a decade in which the global temperature has not changed significantly so such noise is important because it can result in a temperature record being broken even in the absence of an underlying rise. But what does a broken record mean in such a situation? Quite a lot according to Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research, writing in the New Scientist.
Rahmstorf points out that the start of the EL Nino could mean that 2013 might set a global temperature record. Because of this possibility he maintains that now is the time to sort out the anthropogenic signal from the noise in the global temperature records.
Rahmstorf is incorrect in my view when he states that for the past 30 years the global temperature has shown a linear warming trend. True, you can draw a straight line between the start of the recent warming spell – about 1980 – and the latest measurements, and declare the data follows a linear trend. But a straight line does not best represent the data in Hadcrut3, NasaGiss and certainly not in what we have of Hadcrut4. Many scientists have pointed out that there is structure in the temperature data beyond the El Nino/La Nina and the volcanic dips, in particular the standstill in temperature seen in the past 15 years.
Rahmstorf is repeating what happened in 2009 when an El Nino was anticipated for 2010. Nasa’s James Hansen said repeatedly that 2010 could be a record, and in NasaGiss it was, but by only one hundredth of a degree and so statistically insignificant. However the reason for the record was portrayed as anthropogenic global warming and not the temporary, naturally-induced El Nino upward fluctuation above the constant temperature of the past decade or so.
If 2013 is a record year it will prove nothing except that El Ninos drive temperature upward a little bit. To be sure the world is warming again, and after about 15 years of a temperature hiatus the AGW effect must soon start to be greater than the noise in the system very soon, we must see a sustained warming with the majority of the next five or ten years being at first more than two standard deviations and then increasing above the 1997 – 2011 temperature level.
One record year, especially if it’s just a small increase of less than the errors of measurement would, as I am sure Prof Rahmstorf would agree, not prove anything.