Mainstream climate scientists have attacked the interpretations drawn by a new analysis of the effect of the El Nino-Southern Oscillation (ENSO) on global temperatures, which finds that most of the global warming observed in the past 50 years is due to natural occurrences.
The paper, by climate change contrarians John McLean and Associate Professor Bob Carter of the Australian Climate Science Coalition and New Zealand climate scientist Associate Professor Chris de Freitas, describes a close link between the Southern Oscillation Index (SOI) and the temperature of the troposphere, the lower 17-20km of the Earth's atmosphere.
The authors establish that tropospheric temperatures respond to changes in the SOI after a lag of 5-7 months.
They argue that analysis of this link demonstrates that most of the warming—about 70 per cent—observed over the past 50 years can be attributed to the SOI.
"… this study has shown that natural climate forcing associated with ENSO is a major contributor to variability and perhaps recent trends in global temperature, a relationship that is not included in current global climate models," the authors concluded.
The peer-reviewed paper was published on July 23 in the respected Journal of Geophysical Research (JGR).
The paper, and the claims made within and about it, are likely to stir up strong debate in the scientific community, as appears to be the authors' intention.
In a press release issued by the Australian Climate Science Coalition this week, the authors cast aside scientific moderation and take a more direct political line.
"Our paper confirms what many scientists already know: which is that no scientific justification exists for emissions regulation, and that, irrespective of the severity of the cuts proposed, an emissions trading scheme will exert no measurable effect on future climate," said Prof. Carter, one of Australia’s most prominent dissenters against the theory of human-induced global warming.
"The close relationship between the Southern Oscillation and mean global temperature, as described in the paper, suggests future global temperatures will continue to change primarily in response to ENSO cycling, volcanic activity and solar changes."
Scientific responses to the paper will take some time to appear in the JGR, but the preliminary reaction suggests any response will be vigorous.
Professor David Karoly of the University of Melbourne, a lead author on two Intergovernmental Panel on Climate Change (IPCC) reports, said that as far as it goes, the analysis that the paper presents appears sound, but the interpretations the authors have drawn from it are not.
While the analysis describes how the SOI affects short-term year-to-year variations in global mean temperature—a relationship that Prof. Karoly said has been understood in the climate science community since the 1970s—he observes that the paper's notes and press release talk about long-term trends.
"The analysis method used in this paper specifically removes any long-term variations in global mean temperature and in the SOI, and only assesses the year-to-year variations. It then finds that the SOI can explain 70 per cent of the year-to-year variations in global mean temperature after ignoring the effect of volcanoes.
"Using these methods, the paper is unable to make any assessment of the effect of the SOI on long term trends in global mean temperature."
That effect, in Prof. Karoly’s opinion, is "very small".
He also takes exception with the authors' claim that the effects of ENSO are not factored into the global climate models.
"That’s wrong," Prof. Karoly said. "Climate models well represent the relationship between global temperature and SOI, including the lag found in the analysis."