Published online 2 April 2008 | Nature | doi:10.1038/news.2008.728

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Climate challenge underestimated?

Technology will not automatically come to our aid, experts warn.

The challenge of creating technologies to battle climate change may seem smaller than it really is.Getty

Claims that the Intergovernmental Panel on Climate Change (IPCC) has seriously underestimated the challenge and costs of stabilizing greenhouse-gas emissions in the 21st century are fuelling controversy among climate and energy researchers.

Climate policy expert Roger Pielke Jr, climatologist Tom Wigley, and economist Christopher Green lay out in a commentary article published in Nature1 today why they think that the emission scenarios the IPCC produced nearly a decade ago, which are still widely used, are overly optimistic. They note that most of the IPCC’s 'business as usual' emission scenarios assume a certain amount of 'spontaneous' technological change. The size of this assumed change is unrealistic, they argue, and deceives policy-makers and the public about the crucial role policy must have in encouraging the development of technologies to prevent dangerous climate change.

Such a large chunk of the needed energy-efficiency improvements is built in to these 'business as usual' scenarios that the degree of change requiring special effort seems artificially small, they argue. According to the authors' own calculations, IPCC scenarios make it seem as if the technical challenge of stabilizing greenhouse-gas emissions at around 500 parts per million — a concentration which scientists think will prevent average global temperatures from rising more than 2 °C — is a quarter of its true size.

“The paper is a bombshell.”

Marty Hoffert

Richard Tol, an energy and environmental economist at the Economic and Social Research Institute in Dublin, Ireland, also says that the IPCC has underestimated the cost of technology, and notes that the cost of mitigating against climate change increases as time goes on. If Pielke and colleagues are correct, the cost of controlling global warming could go up by a factor of 16, argues Tol.

Going up, going down

“The paper is a bombshell,” says Marty Hoffert, former chair of the Department of Applied Science at New York University. “It explodes the idea that sufficient technology exists to solve the climate and energy problem, and that global warming can be dealt with by market incentives.”

Critics of this argument say that the notion of spontaneous technological change is realistic. They point out that the 0.6% annual improvement in energy intensity that the majority of the IPCC’s business as usual scenarios assume will happen autonomously does match historic trends. On average, global energy intensity has improved by more than 1% per year during the past three decades — and mostly in the absence of noteworthy climate policies.

“The assumptions about the rate of technological change in the scenarios have been thoroughly reviewed and are accepted by the community of technological change experts,” says Bert Metz, who co-chairs the IPCC’s Working Group III on mitigation of climate change.

But there has been little or no improvement in energy intensity during the current decade, and in the past few years the global average has actually worsened. This is largely because of increasing energy demand in countries such as India and China, where cheap, dirty energy is widely used. The jury is out as to whether this decline in energy intensity is the start of a long-term trend, or only temporary, until rising fossil-fuel prices and air-quality problems force Asian nations to modernize their energy systems.

Metz says he is aware that actual economic growth and energy use may develop differently from the IPCC's assumtions, and that this could make it more difficult to reach low stabilization levels. In 2006, the IPCC started to develop new long-term emission scenarios, which will be produced over the coming years.

Heated argument

The IPCC scenarios published in 2000, and still used in the panel's latest 2007 report, encompassed 35 different emissions possibilities. The various scenarios arrive at very different cumulative emissions (and temperature change) by 2100. Actual emissions from 2000–2008 fall within only the highest emission scenarios, the so-called 'A1 scenarios' of booming economic development.

Pielke and colleagues' argument could explain why emissions worldwide are growing faster than ever, and why many industrialized countries are failing to meet their relatively modest Kyoto targets, Hoffert says.

“It's deeply ironic that the IPCC, which has been accused in the past by climate change deniers of exaggerating the threat of adverse climate change, has diminished, or at the very least obscured, the difficulty of controlling it,” says Hoffert.

But others argue that this may not matter, because technological change is now being embraced. “There’s no question that we need deep emission cuts and aggressive action on technology innovation,” says Robert Socolow, co-director of the Carbon Mitigation Initiative at Princeton University in New Jersey. Most OECD (Organisation for Economic Co-operation and Development) countries and US states, if not the US federal government, are already committed to that, he says. So worrying about what happens if technological change isn’t kicked into gear is obsolete, he argues. 

For more views and comments on this story, see 'Are the IPCC scenarios 'unachievable'?' and the assumptions.html">climate feedback blog. Read the commentary and the Nature editorial, and listen to the podcast interview.

  • References

    1. Pielke, R. Jr, Wigley, T. & Green, C. Nature 452, 531-532 (2008)
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