Thursday, January 17th 2013, 10:11 AM EST
The GWPF has been right all along. In a new report Hansen, Sato and Ruedy (2013) acknowledge the existence of a standstill in global temperature lasting a decade.
This is a welcome contribution to the study of global temperature. When others reached the same conclusion they have been ridiculed; so this admission should provide some pause for reflection by those who have attacked the very idea of a recent temperature standstill, often without understanding the data, focusing on who was making the argument and their alleged non-scientific motives.
According to Hansen et al. the Nasa Giss database has 2012 as the ninth warmest year on record, although statistically indistinguishable from the last 12 years, at least. Noaa says it’s the tenth warmest year. The difference is irrelevant.
Hansen discusses the possible contributions to global temperature in the past decade from stochastic variability and climate forcings. Personally I don’t think that the variations are demonstrably stochastic.
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Very early in the report Hansen makes the statement; “Global temperature thus continues at a high level that is sufficient to cause a substantial increase in the frequency of extreme warm anomalies.” To say that such an assertion is debatable is an understatement.
La Nina Years
Hansen has an explanation as to why the year was only the ninth warmest. He says that much of 2012 was affected by a strong La Nina that kept temperatures down. In fact less than half of the year was so affected. In addition, the warming El Ninos and the cooling La Ninas of the past decade or so are not responsible for the standstill in global temperatures. Rather they provide quasi-oscillations around a constant mean. Such is the lack of a trend in global temperatures that a moderate El Nino is enough to push an individual year’s mean temperature to be a record, though still statistically indistinguishable from previous years.
Hansen says; “Comparing the global temperature at the time of the most recent three La Ninas (1999-2000, 2008, and 2011-2012), it is apparent that global temperature has continued to rise between recent years of comparable tropical temperature, indeed, at a rate of warming similar to that of the previous three decades. We conclude that background global warming is continuing, consistent with the known planetary energy imbalance, even though it is likely that the slowdown in climate forcing growth rate contributed to the recent apparent standstill in global temperature.”
I don’t think this is a safe conclusion. Looking at the last three La Nina’s (1999-2000, 2008 and 2011-2012) I think it unwise to use the first one for any comparison. It occurred immediately after the very unusual El Nino of 1998 (said by some to be a once in a century event) and clearly the two subsequent La Nina years must be seen as part of that unusual event. It would be safer not to include 1999-2000 in any La Nina year comparisons. Which leaves us with two, 2008 with a temperature anomaly of 0.49 and 2010-11 which has 0.66 and 0.54. That’s not a great difference, and besides one shouldn’t look for trends with just two datapoints. You cannot conclude anything about background warming from this data.
In addition there is no similar effect in El Nino years; 2002-04 is 0.60 – 0.59, 2006-07 is 0.59 – 0.62 and 2009 is 0.59.
Hansen says that the continual warming since the mid-70s has been associated with greenhouse gasses. His attribution of the global temperature standstill between about 1940 – 1980 as being due to a balance between aerosol cooling and greenhouse gas warming is not as well established as he portrays it; he also contradicts himself when he adds that there is no satisfactory quantitative interpretation of this period because we just don’t know enough. It is also not the explanation that the IPCC attributes to this period which says it can be explained by solar and volcanic effects.
The bottom line is that the recent global temperature standstill is a real event. It is explained in a hand-waving way as due to natural climatic variations masking the long-term trend, even if we do not understand those natural variations. Some believe the standstill might be pointing the way to a deeper revision of our understanding of climate. One thing is clear the stuff you heard until very recently about mankind’s signal of warming being the strongest (and getting stronger) is wrong. The standstill has already taught us that.