Global temperatures in the lower troposphere were +0.21C above the long term average in September, according to data from US company Remote Sensing Systems (RSS).
This means that the so called pause, or hiatus, in global warming has now lasted for exactly 18 years on the basis of the RSS data. The temperature trend from October 1996 to September 2014 is flat.
September 2014 ranks as the 15th warmest in the RSS satellite measured temperature record which dates back to 1979. It follows an anomaly of +0.19C in August which ranked as the 14th warmest August in the RSS record despite announcements from both NASA and NOAA that global surface temperatures – as opposed to tropospheric temperatures – in August were the hottest ever recorded.
The September and August figures from RSS suggest that the rapid warming seen in troposphere the first half of the year, and linked to a nascent El Nino Pacific Ocean warming event, has peaked.
The 18th anniversary of the pause as measured by RSS data has no special scientific significance. In September a paper was published with a statistical analysis of global temperature data that indicated that, statistically speaking, the pause actually dates back 26 years on the RSS data set once the uncertainties in the data are taken into account.
Ross McKitrick from the Department of Economics at the University of Guelph in Canada, who wrote the paper, is seen as skeptical about global warming, and in the past he has been highly critical of the statistics behind the “hockey-stick” graph which shows global temperatures remaining broadly flat for much of the last 1,000 years before rising sharply during the 20th century.
McKitrick used surface temperature data from the HadCRUT 4 series maintained by the UK Met Office as well as the two series of satellite measurements of the temperature of the lower troposphere that are maintained by the University of Alabama in Huntsville (UAH) and by RSS of the US.
In the conclusion to the open-access paper, McKitrick wrote that in the Met office surface data “we compute a hiatus length of 19 years, and in the lower tropospheric data we compute a hiatus length of 16 years in the UAH series and 26 years in the RSS series”.
The existence of the pause in global warming was acknowledged by the Intergovernmental Panel on Climate Change last year but there has been significant debate about the actual duration of this hiatus with some commentators alleging that the length is exaggerated by cherry-picking the start date as 1998 – a particularly warm year.
McKitrick says that the statistical analysis technique he used avoids potential biases and is immune to the charge of cherry-picking.