The stabilisation myth

Although politicians and policy-makers are keen to believe that if we stabilise carbon emissions we can also stop global warming, new research suggests that this might not be the case. Clive Hamilton exposes the disturbing truth
The belief that we can stabilise the climate at a specified concentration of greenhouse gases in the atmosphere, with an associated increase in average global temperature, has underpinned all international negotiations over global warming. The idea that greenhouse gas emissions must be limited to prevent ‘dangerous’ warming is embodied in the 1992 Framework Convention on Climate Change. The official European and Group of Eight goal of aiming to keep warming below 2°C is based on this idea, as are greenhouse gas concentration targets such as 450 parts per million (ppm) or 550 ppm advocated in the Stern report and Australia’s Garnaut report.

But the belief that humans can adopt policies that stabilise the climate rests on assumptions that aren’t well founded in the science. Stabilisation requires that annual emissions are eventually reduced to ‘the level that balances the Earth’s natural capacity to remove greenhouse gases from the atmosphere’. The problem is that global warming is likely to trigger its own ‘natural’ sources of new emissions and interfere with the Earth’s capacity to remove carbon from the atmosphere.

Policy knobs
The Earth’s climate is not like a machine whose temperature can be regulated by turning some policy knobs; it’s a highly complex system with its own regulatory mechanisms. Humans cannot regulate the climate; the climate regulates us. For several years, climate scientists have understood that some of the relationships among variables are non-linear, so that a slight increase in warming can cause a large shift in other aspects of the climate. Paleoclimatologists have known this for a long time, but it’s only recently that the idea has been linked explicitly to today’s global warming.

If we look at a chart showing the Earth’s climate history stretching back over many millennia, we don’t see smooth transitions from ice ages to ‘interglacial’ or warm periods (such as the one we are now in). The transitions are sometimes dramatic, with sharp changes in climate occurring over mere decades, probably due to amplifying feedback effects. So climate states can end abruptly once certain thresholds are crossed, setting off accelerated warming that is stopped only when a natural limit is reached, such as the disappearance of ice from the Earth.

There are numerous tipping points that could induce positive-feedback effects that amplify warming and its effects, including the disappearance of summer sea-ice in the Arctic, the melting of the Greenland ice sheet, the melting of the West Antarctic ice sheet, the release of carbon from melting permafrost, and large-scale dieback of the Amazon rainforest. As they occur, these changes will be effectively irreversible, at least for thousands of years.

A recent paper has destroyed any idea we might have that we can take radical corrective action once things become intolerable. It reaffirms that a large proportion of the CO2 we are putting into the atmosphere will still be there in 1,000 years, so the level at which emissions peak makes a huge difference. Both the warming and the sea-level rise associated with that peak will not decline, even if emissions fell to zero, but will stay virtually constant for more than a millennium. The authors conclude: ‘It is sometimes imagined that slow processes such as climate change pose small risks, on the basis of the assumption that a choice can always be made to quickly reduce emissions and thereby reverse any harm within a few years or decades. We have shown that this assumption is incorrect…’

The lag between emissions and their effects on climate and the irreversibility of those effects make global warming a uniquely dangerous and intractable problem for humanity. Among other things, these features of climate change render standard economic analysis of the problem hopelessly inappropriate. Indeed, it is positively dangerous.

Private panic
Recognition of the non-linear nature of climate change has radically transformed the climate-science debate in the past few years, although the message is still to filter out of the scientific community and into policy deliberations. It is the reason many climate scientists are no longer merely worried but panicked, although the panic is sometimes suppressed by a practised detachment. As late as 2007, the IPCC was still writing as if stabilisation were feasible, although buried in its report was a muted but ominous warning: ‘The risk of climate feed-backs is generally not included in the above analysis. Therefore, the emission reductions to meet a particular stabilization level reported in the mitigation studies assessed here might be underestimated.’

After their 2008 review of the dangers of climate tipping points, a group of leading climate scientists wrote: ‘Society may be lulled into a false sense of security by smooth projections of global change.’ This is typical of the cool understatement of so much climate science. The extent to which policy-makers and their advisers have been lulled into a false sense of security is apparent from the sudden emergence of ‘overshooting’ strategies, now adopted explicitly or implicitly by almost every government in the world.

The rot set in around 2005 when key policy advisers seem to have decided that aiming to stabilise atmospheric concentrations of greenhouse gases at 450 ppm of carbon dioxide equivalent (CO2-e), the level associated with ‘dangerous’ warming of 2°C, would be too difficult. The capitulation was announced by the UK’s chief scientist, David King, who declared that aiming for 450 ppm would be ‘politically unrealistic’. The same conclusion was drawn by Nicholas Stern, who wrote in his 2006 report that aiming for stabilisation at 450 ppm ‘would require immediate, substantial and rapid cuts in emissions that are likely to be extremely costly’.

Instead, the world should aim to stabilise at a politically achievable 550 ppm, a target also taken up by Ross Garnaut in his 2008 report for the Australian government. After all, the reasoning goes, we are already at 430 ppm CO2-e, and stopping at 450 would meet fierce opposition from industry and voters. So we must aim instead for a concentration of 550 ppm and then bring it back down to 450 ppm in the following decades.

This is the path adopted by the Obama administration, too. Rich-country emission cuts of 25–40 per cent below 1990 levels by 2020, which are necessary if the world is to aim for a target of 450 ppm, were immediately declared politically impossible by the new US special envoy for climate change, Todd Stern. The ‘most ambitious’ proposal the USA could aim for would be to return emissions to 1990 levels by 2020 – a ‘zero per cent’ reduction instead of 25–40 per cent – although the climate change legislation passed last year by the House of Representatives subsequently set a nominal target of four per cent below 1990 levels. ‘At the same time, we are being guided by the science and doing the math,’ said Stern, ‘we cannot forget that we are engaged in a political process and that politics, in the classic formulation, is the art of the possible. Of course we cannot afford to be passive in our understanding of that principle – we need always to push the envelope of what is possible.’ The British and American Sterns were at one.

No turning back

Faith in our ability to overshoot then return to a safer climate simply fails to understand the science – whatever we do, we will be stuck with the results for a very long time. If CO2 concentrations reach 550 ppm, after which emissions fell to zero, the global temperature would continue to rise for at least another century. Moreover, once we reach 550 ppm, a number of tipping points will have been crossed, and all the efforts humans then make to cut their greenhouse-gas emissions may be overwhelmed by ‘natural’ sources of greenhouse gases. In that case, rather than stabilising at 550 ppm, 550 will be just another level we pass through one year on a trajectory to who knows where – 1,000 ppm perhaps.

In September 2008, two scientists from the Scripps Institution of Oceanography in the USA published an analysis arguing that the world is already committed to 2.4°C of warming above pre-industrial levels. With that degree of warming, the Earth would pass at least three climate tipping points – the disappearance of Arctic summer sea-ice, the melting of the Himalayan–Tibetan glaciers and the melting of the Greenland ice sheet.

The analysis was challenged by another eminent scientist, Hans Schellnhuber, who argued that the claim that we cannot avoid at least 2.4°C of warming depends on two pivotal assumptions: that the world will not be able to reduce global greenhouse gas concentrations below 2005 levels, and that developing countries will implement the sorts of ‘clean air’ policies the West has used to reduce urban air pollution. The latter policies are expected to reduce the ‘atmospheric brown cloud’ made up of aerosols that mask the effect of warming. When the skies are cleared of the particles that create global dimming, the full effects of the enhanced greenhouse effect will be felt.

Schellnhuber believes that global greenhouse gas emissions can be halved by 2050. This depends, however, on assuming that developing countries do not move too quickly to clean up air pollution, for if they do, temperatures would indeed shoot up close to 2.4°C before coming down to perhaps below 2°C a century or so later. Schellnhuber’s argument asks us to be optimistic about policies to reduce greenhouse-gas emissions and pessimistic about the implementation of policies to reduce air pollution. Even he concedes that the possibility of keeping temperatures at or below 2°C depends vitally on the world ensuring that emissions peak in the period 2015–20.

This is an edited extract from Requiem for a Species: Why We Resist the Truth About Climate Change by Clive Hamilton (Earthscan, £14.99)

August 2010

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