Tim Flannery’s radio statement: “If the world as a whole cut all emissions tomorrow, the average temperature of the planet’s not going to drop for several hundred years, perhaps over 1000 years” comes following 30 years since pioneering peer-reviewed climate scientists, such as Wally Broecker, James Hansen and Barrie Pittock, began to warn the world of the consequences of open-ended carbon emissions.

According to the fourth ICCP “about 50% of a CO2 increase will be removed from the atmosphere within 30 years and a further 30% will be removed within a few centuries”.

However, in more recent publications climate scientists of the University of Victoria state, among other:  “…While a few centuries may be an appropriate absorption time scale for relatively low levels of emissions, recent studies show it may take thousands of years to absorb half of the CO2 we could potentially emit in the next few hundred years.”

And: “…for emissions similar to known fossil fuel reserves (~ 5000 Pg [= 5000 billion ton]), the time to absorb 50% of the CO2 is more than 2000 years.”

And “We also find that the maximum surface air temperature anomaly is even longer lived than anthropogenic CO2 and that two thirds of the maximum temperature anomaly may persist for more than 10,000 years. For ecosystems that have adapted to a warmer world, slow cooling may be beneficial. Nevertheless, it is sobering to consider that the carbon we emit over a handful of human lifetimes may significantly affect the earth’s climate for tens of thousands of years.”

The paper Lifetime of Anthropogenic Climate Change: Millennial Time Scales of Potential CO2 and Surface Temperature Perturbations by Eby et al. 2009 states:

“It is found that the time required to absorb anthropogenic CO2 strongly depends on the total amount of emissions; for emissions similar to known fossil fuel reserves, the time to absorb 50% of the CO2 is more than 2000 yr. The long-term climate response appears to be independent of the rate at which CO2 is emitted over the next few centuries. Results further suggest that the lifetime of the surface air temperature anomaly might be as much as 60% longer than the lifetime of anthropogenic CO2 and that two-thirds of the maximum temperature anomaly will persist for longer than 10,000 yr. This suggests that the consequences of anthropogenic CO2 emissions will persist for many millennia.”

Instrumental measurements of CO2 and temperatures for the period 1800-2000 suggest consistent overall rise in these parameters, sharply rising from about 1965-1970 (Figure 1).

Historical changes in CO2 and Surface Air Temperature

Model CO2 rise projections, depending on emission scenarios, suggest the rise of CO2 to ~700-800 parts per million for “low” total emission of 1920 billion ton CO2 and to 2200 ppm for extreme emission scenario of 5120 billion ton CO2 (Figure 2).

Model simulation of future changes in atmospheric CO2 composition under differentemission scenarios (1 Pg = 1 billion ton CO2)

In Eby et al’s  projections peak temperature anomalies will range between 2.5 and 8 degrees above the present for different emission scenarios (Figure 3), representing sharp shifts of the atmosphere/ocean system to conditions which existed about 3 million years ago and before 40 million years ago, respectively.

Model simulation of future changes in Surface-Air Temperature (SAR) under different emission scenarios (1 Pg – 1 billion ton CO2).

Claims as if the atmospheric residence time of CO2 is about five years apply for individual molecules within the ~200 billion ton annual atmosphere-ocean-biosphere cycle, but neglect the cumulative effect, manifested by the rise in CO2 from 280 ppm early in the 19th century to 391 ppm at present.

Claims as if CO2 rise is driven by temperature apply within the context of the amplifying feedback effects of current global warming but ignore the fact that, whereas glacial terminations were driven by orbital forcing, ice melt and CO2 feedbacks, current climate change is driven by the more than 320 billion ton carbon emitted by human industry. Figure 4 indicates where this carbon now resides:

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Peter Fray
Peter Fray
Editor-in-chief of Crikey
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