Friday, November 30th 2012, 2:10 AM EST
It’s that time of year again when some call the global annual average temperature for the year, even though there are still two months of data remaining. Such a premature declaration is done for political reasons, such as the current UN climate meeting in Doha.
The UK Met Office, on the 28th November 2012, issued a ‘State of global temperatures in 2012,’ and it makes interesting reading.
The Met Office uses three “leading global temperature datasets” to conclude that the average temperature of 2012 is 0.45 +/- 0.10 deg C above the 1961-90 average. They add that these error bars mean that 2012 could be between the 4th and the 14th warmest year of the instrumental period, since 1850. Realistically though it’s going to be ninth or tenth. Fig 1 (left) shows the Met Office data.
The Met Office then adds that due to a La Nina 2012 is cooler than the average for the last decade. Statistically speaking that is not the whole story. According to the data we already have, taking the errors into account, 2012 is statistically identical to all the other years of the past decade and beyond. The recent global temperature standstill continues.
What is an obvious standstill to some – the global temperature hasn’t increased for 15 years – is to others a not so rapid warming, or as the Met Office puts it; “Although the first decade of the 21st century was the warmest on record, warming has not been as rapid since 2000 as over the longer period since the 1970s.”
The Met Office continues: “This variability in global temperatures is not unusual, with several periods lasting a decade or more with little or no warming since the instrumental record began. We are investigating why the temperature rise at the surface has slowed in recent years, including how ocean heat content changes and the effects of aerosols from atmospheric pollution may have influenced global climate.”
Now I beg to differ. Since instrumental temperature records began in about 1850 lengthy standstills, such as the one between 1940 – 80, are evident. But we are not in that regime. We are supposed to be in the era of anthropogenically-dominated global warming. The IPCC put the transition between natural and anthropogenic influence as 1960-80. Since the global temperature started to rise about 1980, and continued to 1997, this makes the lack of variability seen in global temperatures since 1997 highly unusual. Indeed, as we have said before, it is the recent warm periods major characteristic, and climate models strain to account for it.
The Met Office carries on: Interannual variations of global surface temperature are strongly affected by the warming influences of El Niño and the cooling influences of La Niña in the Pacific Ocean. These are quite small when compared to the total global warming since 1900 of about 0.8 °C but nevertheless typically reach about +/- 0.10 °C, and can strongly influence individual years.
True, but a more pertinent point is that El Nino and La Nina have no effect on the 15-year global temperature standstill. Individual years go up and down due to these effects, but there is no statistically significant trend since 1997. In fact looking at the post-1997 data the El Nino and La Ninas seem to be the only statistical cause of variations from year to year.
Last year the Met Office said that 2011′s placing near the top of temperature datasets, which go back to 1850, continues a long-term warming trend in global climate. (Actually 2011 was even cooler than 2012, last year the Met Office put it as 11th warmest).
Again, the long-term warming trend is true if you combine the natural and AGW era, but not if one just considers the AGW period. Taking away 2012’s temperature from the recent data doesn’t make much difference, yet at the end of 2011 we had “the warming trend continues”, but after just one more year of data we now have “temperature rise at the surface has slowed.” If there is evidence that at the end of 2012 it has slowed, then there was also evidence it had slowed at the end of 2011.
To summarise: There is no point in putting out conclusions about the global temperature for any year until all that year’s data is available. It is misleading to only say that the global temperature rise has slowed down since 1980, when the evidence is that it has remained unchanged for the last 15 years.
The 15-year standstill is a real feature in the data. Arguments that it has been cherry picked are irrelevant. The climate models give probabilities of global temperature standstills – the longer the standstill the lower the probability. Such models do not make any stipulation other than the duration of the standstill, not its place in the dataset. The standstill is El Nino-La Nina independent.
It seems that the release of a years global temperature before the year has ended is a statistical dance we have to go through every year. But those who make decisions based on the Met Office press release announcing the year’s temperature do so without a complete picture.