G8 climate target questioned—Is a commitment to prevent global temperatures from rising more than 2…

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http://www.nature.com/news/2009/090715/full/460313a.html

Published online 15 July 2009 | Nature 460, 313 (2009) | doi:10.1038/460313a

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G8 climate target questioned

Is a commitment to prevent global temperatures from rising more than 2 °C enough?

Quirin Schiermeier

The path to a meaningful deal at the Copenhagen climate summit in December seems more treacherous in the wake of last week's meeting of the G8 nations.

Leaders gathered in the quake-struck Italian town of L'Aquila promised to try to prevent global temperatures from rising more than 2 °C above pre-industrial temperatures. They also said that rich countries would cut their aggregated greenhouse-gas emissions by 80% by 2050, and, with other countries, would cut global emissions by 50% over the same period. But they made no commitment to reducing emissions any earlier and did not agree on a base year against which to measure national emissions cuts.

The choice of base year "matters a great deal", says Gwyn Prins, an economist at the London School of Economics. A recent year, say 2005, would make targets easier to achieve for countries such as Canada, Japan and the United States, whose economies and emissions have grown constantly over the past 20 years. It would be even more attractive for booming countries such as China and India. But the European Union would benefit from a 1990 baseline — as emissions there have fallen since then — as would Russia, which saw a dramatic industrial decline in the 1990s.

Others argue that the 2 °C limit is, in fact, a crucial commitment because it marks the first time G8 countries have agreed on what constitutes 'dangerous' climate change. Two degrees warming translates with "mathematical clarity" into the required "decarbonization" of the global economy, says Hans Joachim Schellnhuber, director of the Potsdam Institute for Climate Impact Research in Germany. A study earlier this year, for example, suggested that there is a 50% chance that global warming will exceed 2 °C by the end of the century if around 1,400 billion tonnes of carbon dioxide is emitted during the period 2000–50 (http://www.nature.com/uidfinder/10.1038/nature08017">M. Meinshausen et al. Nature 458, 1158–1162; 2009). Emissions for 2000–06 alone amounted to around 234 billion tonnes.

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