Phil Jones, the United Kingdom scientist who was targeted in the “ClimateGate” affair, now says global warming since 1995 is statistically significant, a year after telling BBC News that post-1995 warming was not significant.
He noted that a year worth of data had pushed the trend past the threshold typically used to assess whether trends are in fact “real.” Jones said this shows the importance of using longer records for analysis.
Scientists generally use a minimum threshold of 95 percent to assess whether a trend is likely to be down to an underlying cause, rather than emerging by chance. If a trend meets the threshold, it generally means that the odds of it being down to chance are less than one in twenty.
Jones said last year’s analysis, which went back to 2009, did not reach this threshold — but adding data for 2010 puts it over that line.
“The trend over the period 1995-2009 was significant at the 90% level, but wasn’t significant at the standard 95% level that people use,” Jones told BBC News.
“Basically what’s changed is one more year [of data],” he noted. “That period 1995-2009 was just 15 years – and because of the uncertainty in estimating trends over short periods, an extra year has made that trend significant at the 95% level which is the traditional threshold that statisticians have used for many years.”
“It just shows the difficulty of achieving significance with a short time series, and that’s why longer series – 20 or 30 years – would be a much better way of estimating trends and getting significance on a consistent basis,” he added.
Jones’ 2010 comment in a BBC News interview, is routinely quoted inaccurately — as demonstration that the Earth’s surface temperature is not rising.
HadCRUT3, one of the main global temperature records used by bodies such as the Intergovernmental Panel on Climate Change (IPCC), is compiled by a joint effort between the Climatic Research Unit (CRU) at the University of East Anglia (UEA), where Jones is based, and the UK Met Office.
HadCRUT3, which Jones helps compile, shows warming 1995 – 2010 of 0.19C — consistent with the other major records, which all use slightly different ways of analyzing the data in order to compensate for issues such as the dearth of measuring stations in polar regions.
Shortly before the Copenhagen Climate Summit in December 2009, Jones found himself at the center of the affair that came to be known as “ClimateGate,” which saw the release of more than 1,000 emails taken from a CRU server.
Many critics alleged that the emails showed CRU scientists attempting to undermine the usual processes of science, and of manipulating data in order make global warming seem much worse. Subsequent inquiries found the scientists did fall short of best practice in some areas, but found no evidence of manipulation.
Since then, nothing has emerged through mainstream science to challenge the IPCC’s picture of a world warming through greenhouse gas emissions. And a new initiative to develop a global temperature record, based at Stanford University in California whose funding includes “climate skeptical” organizations, has reached early conclusions that match established records closely.
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