The awful arithmetic of global warming

With all the debate and the headlines around broken promises, increased costs, lost jobs and displaced industries, it is sometimes easy to forget what everyone was arguing about in the first place – the science of climate change.

The science is the subject of Professor Ross Garnaut’s 5th update of his 2008 Climate Change Review and his general conclusion is bleak. He says he wishes it wasn’t so, but the science of climate change as underlined by the 2007 report from the International Panel on Climate Change has been confirmed by subsequent observations and reports, and merely strengthen the case of rising global temperatures, and of man’s contribution to it.

These including measurements of the rise in average global temperatures, which are tracking at the mid point of the IPCC forecasts - and show no evidence of of a weakening or reversing trend, as suggested by some commentators – and of sea levels and the impact on the physical and biological environment, which are all developing at the top end of the IPCC forecasts.

In Australia since 1910, annual average temperatures have increased by 0.9°C,and while 2005 is still the hottest year on record, based on the mean annual temperature across Australia, 2009 was the second-warmest year. “The decade ending in 2010 has easily been Australia‘s warmest decade since record keeping began and continues a trend of each decade being warmer than the previous that extends back to the 1940s," his report says. The milder year in 2010 demonstrates that individual years can still be relatively cool even as the warming of Australia‘s climate continues.”

The Garnaut update concludes that the oceans are warming, with more than 90 per cent of the extra heat stored by the earth's systems in the last 50 years is found in the ocean; sea levels are continuing to rise at a rate considerably higher than the average rate over the 20th century; the acidity of oceans has increased by 30 per cent since pre-industrial times; and the area and mass of melt from the Greenland Ice Sheet is continuing to increase.

“The awful reality is that no major developments of science hold out realistic hope that the judgment (of the IPCC) over-estimated the risks,” Garnaut says.

If anything, the estimates and predictions shown in that report will prove to be conservative, he says, and there could be a case for aiming at a bolder target than limiting greenhouse emissions at 450 parts per million – the figure that it is generally agreed will lead to average global temperature rises of around 2°C.

Garnaut spends much time talking about the “scholarly reticence” in the science community and their tendency to “pull their punches” because of the risk of undue public criticism. He said it is considered “more scholarly” to be conservative and wrong rather than radical and right. "There must be a possibility that scholarly reticence, extended by publications lags, has led to understatement of the risks," he writes.

He cites the issue of Antarctic and Greenland ice sheets, which have not been included in the IPCC predictions of sea level rises. “It was disconcerting to find the specialists in both hemispheres, to whom I spoke personally, expressing private opinions that there would be a contribution from Greenland and west Antarctica to sea level rise this century of uncertain, but substantial and possibly greatly disruptive, dimension,” he writes. “All declined to put private views on the public record, because the views were not yet reflected in the peer-reviewed scientific literature.”

Of course, no such inhibitions have afflicted those who contest the science. Garnaut says the increased doubts expressed in the public domain, particularly in Australia, the US and some European countries, have come from the prominence of sceptical and dissenting views, and the support they receive in the popular press. “If you take our mainstream media it will often seek to provide some balance between those who base views on the mainstream science and those who don’t,” Garnaut says. “It’s a strange sort of balance. It’s a balance of a number of words and not of scientific authority.”

The issue about global targets is an interesting one. Garnaut argues that the extra costs of going to 450ppm rather than the 550ppm scenario – as entertained under the government’s bipartisan commitment to 5 per cent cut in emissions from 2000 levels by 2020 – would be well justified against the costs of not doing so.

He also says there is a strong argument for trying to achieve a cap of 350ppm – as recognised in a clause included under the Cancun agreement, and vigorously promoted by some environmental groups and the most exposed island and African nations. But he says here is little point in aiming for such a target when there is still not a credible path agreed for 450ppm. Indeed, the world is on a path to overshoot the 450ppm target by a considerable margin.

For the world to hold emissions concentrations to 550 ppm carbon dioxide equivalent would require an “achievement of international cooperation and national economic policy innovation of large dimension”. To achieve 450 ppm carbon dioxide equivalent with only the degree of overshooting envisaged in the Review would be an “international relations and national public policy achievement of historic dimension.”

“This is the awful arithmetic of strong mitigation of climate change. To have any chance of achieving a goal tighter than 450 ppm carbon dioxide equivalent requires the international community (with Australia playing its proportionate part) soon to define a credible path to that goal. The discussion in the science of 350 ppm sits there as a warning of danger, but with no prospect of serious adoption as a goal of concerted international policy action.”