Late 20th century warming not primarily man made

A new research paper has been published by local ACM heroes Bob Carter, John McLean and Chris de Freitas which argues that the majority of the late 20th century warming was caused by factors other than man. I guess the pollies will ignore this like they ignore any other research that doesn't obediently suck up to the "consensus" of man-made global warming [surely "climate change" - Ed]. And anyway, the science is settled, right? Debate's over, you denier you.

Nature not man responsible for recent global warming

Three Australasian researchers have shown that natural forces are the dominant influence on climate, in a study just published in the highly-regarded Journal of Geophysical Research. According to this study little or none of the late 20th century global warming and cooling can be attributed to human activity.

The research, by Chris de Freitas, a climate scientist at the University of Auckland in New Zealand, John McLean (Melbourne) and Bob Carter (James Cook University), finds that the El Niño-Southern Oscillation (ENSO) is a key indicator of global atmospheric temperatures seven months later. As an additional influence, intermittent volcanic activity injects cooling aerosols into the atmosphere and produces significant cooling.

"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" says corresponding author de Freitas.

"We have shown that internal global climate-system variability accounts for at least 80% of the observed global climate variation over the past half-century. It may even be more if the period of influence of major volcanoes can be more clearly identified and the corresponding data excluded from the analysis.”

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. 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.

"When climate models failed to retrospectively produce the temperatures since 1950 the modellers added some estimated influences of carbon dioxide to make up the shortfall," says McLean.

And Bob Carter, a vehement opponent of any ETS in Australia sums up the effect of this on policy:

“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, ETS will exert no measurable effect on future climate.”

But don't expect Rudd, Wong or Turnbull to take the slightest bit of notice.

Read the full abstract here (h/t Climate Depot)