The opening statement of Garnaut’s Review (Supplementary Draft Report, 5.9.08) states:

“There are moments in the history of humanity when fateful choices are made. The decision over the next few years on whether to take strong action to mitigate human-induced climate change is one such moment.”

This stands in stark contrast to the Review’s recommendation “The only option for Australia at this time is to pursue global agreement to stabilise atmospheric greenhouse gas concentrations at 550 ppm.” A 10% cut relative to 2000 in Australian carbon emissions by 2020 is recommended as “First Best conditional offer”.

Atmospheric CO2 levels about 550 ppm are well above the level at which the polar ice sheets formed, estimated as 450 ppm by leading US climate and paleo-climate scientists.

These authors state:

Decreasing CO2 was the main cause of a cooling trend that began 50 million years ago, large scale glaciation occurring when CO2 fell to 425±75 ppm, a level that will be exceeded within decades, barring prompt policy changes. If humanity wishes to preserve a planet similar to that on which civilization developed, paleoclimate evidence and ongoing climate change suggest that CO2 will need to be reduced from its current 385 ppm to at most 350 ppm. The largest uncertainty in the target arises from possible changes of non-CO2 forcings. An initial 350 ppm CO2 target may be achievable by phasing out coal use except where CO2 is captured and adopting agricultural and forestry practices that sequester carbon. If the present overshoot of this target CO2 is not brief, there is a possibility of seeding irreversible catastrophic effects.

The Garnaut Review has generally accepted the scientific judgments of the IPCC, “on a balance of probabilities”, as a reasonable source of scientific knowledge on climate change. The IPCC 2007 4th Assessment report essentially assumes linear climate trajectories and equilibrium climate sensitivity, albeit with proviso “Feedbacks can amplify or dampen the response to a given forcing.”

However, the magnitude of feedback effects as triggers of climate tipping points has been underestimated in the IPCC reports and the Garnaut Review.

New studies of the recent history of Earth indicate feedback mechanisms, including ice sheet melt, loss of ice albedo, warm water effects on ice melting, carbon cycle feedbacks and methane release, act as major forcing for climate tipping points and extreme atmospheric events, occurring over short periods of several decades to several years (e.g. Steffensen et al., Science Express, 19 June 2008; Kobashi et al., 2008, Earth Planet. Sci. Lett., 268, 397–407).

The fast disappearance of Arctic Sea ice (23% spring melt reduction in 2006-2007), heralding an opening of open water ocean and a new climate regime for the northern hemisphere, and mid-winter break-up of the West Antarctic Wilkins ice shelf, suggest the IPCC’s and Garnaut’s time tables are superseded by the pace of climate change.

For a government elected on the promise of effective measures of climate mitigation, even global leadership in emission control and clean energy technologies, Kevin Rudd’s recent statements “there is always going to be argy-bargy in the political debate” and “my experience is not all scientists agree and you can have people who have different views”, sounds like a familiar echo of a previous Prime Minister’s statements.