A study by three Australasian researchers just published in the Journal of Geophysical Research shows that most of the late 20th century global warming and cooling can be attributed to natural climate processes.
The research paper by Associate Professor Chris de Freitas, a climate scientist at the University of Auckland in New Zealand, and two science advisors to the Australian Climate Science Coalition, John McLean and Professor Bob Carter, finds that the Southern Oscillation is a key indicator of changing global atmospheric temperatures seven months later.
The findings follow research released earlier this month by US scientists which shows that maximum solar activity and its aftermath have impacts on earth that resemble La Niña and El Niño events in the tropical Pacific Ocean.
In a statement to the media, lead author John McLean said that when climate modellers could not accurately determine historical temperatures "they added a 'human influence' to their models".
"This paper shows that the missing component was the El Niño-Southern Oscillation (ENSO)," Mr McLean said.
"The difference in output when using these two factors is that one predicts a continuing rise in temperature and the other predicts fluctuations according to the ENSO.
"The data particularly over the last 10 years indicates that the latter is correct.
"The IPCC acknowledges in its 4th Assessment Report that ENSO conditions cannot be predicted more than about 12 months ahead so until that situation improves projected global temperatures are likely to be quite inaccurate."
The group says that the surge in global temperatures since 1977 can be attributed to a 1976 climate shift in the Pacific Ocean that made warming El Niño conditions more likely than they were over the previous 30 years and cooling La Niña conditions less likely.
"We have shown that internal global climate-system variability accounts for at least 70 per cent of the observed global climate variation over the past half-century," Associate Professor de Freitas said.
Climate researchers have long been aware that ENSO events influence global temperature, for example, causing a high temperature spike in 1998 and a subsequent fall as conditions moved to La Niña.
The groups says it is also well known that volcanic activity has a cooling influence, and as is well documented by the effects of the 1991 Mount Pinatubo volcanic eruption.
The new paper draws these two strands of climate control together and shows by demonstrating a strong relationship between the Southern Oscillation and lower-atmospheric temperature, that ENSO has been a major temperature influence since continuous measurement of lower atmospheric temperature first began in 1958.
According to the three researchers, ENSO-related warming during El Niño conditions is caused by a stronger Hadley Cell circulation moving warm tropical air into the mid-latitudes.
During La Niña conditions the Pacific Ocean is cooler and the Walker circulation, west to east in the upper atmosphere along the equator, dominates.
Professor Bob Carter, one of four scientists who recently assisted Senator Steve Fielding in questioning the justification for the proposed Australian emissions trading scheme, says that this paper has significant consequences for public climate policy.
"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," Prof. Carter said.
"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."
* The research paper abstract can be viewed by clicking here.