Slowing CO2 Growth Contradicts Consensus Claims
AVERAGE growth in atmospheric carbon dioxide has slowed since early last decade, at a time when reported emissions increased at an unprecedented rate, an Australian-led study suggests.
An Australian-led study suggests that averaging carbon dioxide measurements from a large number of sites is not the best way to determine global trends. Picture: Thinkstock
The international study, reported today in the journal Nature Climate Change, attributes the discrepancy to an early underestimate in reported global emissions.
The findings, based on over 20 years of observations from Cape Grim in Tasmania, suggest a reported “surge” in emissions between 2000 and 2008 reflects a bias in the early emissions.
The accumulation of atmospheric carbon between 1994 and 2002 was underestimated by some nine billion tons, the paper suggests.
It says post-2000 emissions are tracking in the middle of the range of emission scenarios produced by the Intergovernmental Panel on Climate Change.
Roger Francey, an honorary fellow with CSIRO’s Centre for Australian Weather and Climate Research, said the study provided an alternative method of verifying global CO2 emissions.
The conventional approach involves totalling “bottom-up” estimates of national energy production and use.
Anthropogenic emissions are added to the amount of carbon dioxide added or removed naturally by the oceans and the terrestrial biosphere, and the amount that accumulates in the atmosphere.
The total accumulation is usually derived by averaging CO2 measurements from up to 90 sites around the world. “This introduces large uncertainty in trends since many sites, particularly northern hemisphere sites, are influenced by regional [industry] and more complex meteorology,” Dr Francey said.
“There’s considerable error when you add that together to get a global total.”
He said the Cape Grim site was unique because of its access to the ‘clean’ air of the Roaring Forties.
It measured samples of air which had travelled thousands of kilometres across the Indian and Southern Oceans without being influenced by land or industry. This made it a reliable gauge of background CO2 trends.
Dr Francey said local measurements were essential to gauge regional and national emission reductions. “But that is not the best way to get global totals,” he said.
“What’s actually happening in terms of climate warming or ocean acidification depends on the average CO2 in the whole atmosphere.”