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Stabilization targets
Our goal is to stabilize the Earth's climate system. The question is, at what temperature? How much warming can we have before we reach dangerous levels of interference in the climate?
As you can see from the chart, taken from the British government's Stern review, even a few degrees of warming puts us at risk of very serious consequences. With 2° C of warming we are expected to lose most mountain glaciers (threatening water supplies), have mass extinction of species, and possible onset of melting of the large ice sheets. Based on these risks, should we not stabilize temperature as close to pre-industrial levels as possible? According to the latest IPCC report, at 1.9° C, we run a significant risk of irreversible loss of the Greenland ice sheet. Other studies suggest that at 2° C we risk losing the entire Amazon rainforest. These aren't certainties, but they are real risks. Based on these risks, we believe it is imperative to stabilize the Earth's climate system below 2° C of warming -- as far below as possible. This is similar to but stronger than the official policy of the European Union, which is to not exceed 2° C. What does this temperature target mean in terms of emission cuts? There is a good deal of uncertainty here, because the relationship between greenhouse gas concentrations and temperature rise is not known with precision. However, we know that doing nothing will lead to such high levels of greenhouse gases that we are nearly certain to exceed 2° of warming by a large margin. A common estimate is that we need to cut emissions 80% below current levels by 2050. Although we need emissions targets such as this, there are two major caveats: 1. This figure applies to global emissions, not just U.S. and Europe. China will be the world's largest emitter by 2010, and emissions from developing nations will exceed those from developed nations by 2015. Unless we figure out how to get the developing nations onto a clean energy path, we can't possibly meet these targets. 2. This figure assumes that the land and oceans will continue to absorb about half our emissions (thus keeping them out of the atmosphere), as they do currently. But recent research strongly suggests that this effect is likely to weaken as concentrations rise, possibly quite substantially. This means that we may need cuts that are even steeper. Any serious effort to meet this stabilization target will therefore not rely on a fixed level of emissions cuts, but insist that these emission targets be regularly updated by the best available science. Sources
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