Reducing greenhouse gases now may lower climate change risk

A new climate analysis by scientists at the Massachusetts Institute of Technology and elsewhere, which focuses on probability outcomes, finds that even moderate reductions in greenhouse gas emissions now will significantly lower the risks of dramatic, future climate change.

The analysis also indicates that, to avoid a temperature increase of more than 2 degrees C (3.6 degrees F.) above preindustrial levels — an oft-discussed goal — these emissions reductions had better come soon. If not, say the researchers, dramatic changes in climate driven by feedback loops will become difficult — and perhaps impossible — to control.

The analysis lays out climate salvation in terms of odds. We still have around a 50-50 chance, it says, of stabilizing climate and avoiding a temperature increase of much more than 2 degrees C. (That's supposed to be encouraging, by the way.) Generally, scientists think that keeping temperature increases to no more than that will avoid dramatic sea level rise, as well as a disruption of agriculture and natural ecosystems.

Here's what needs to happen in order to fall on the right side of that 50-50 odds ratio, say the authors:

In the US, we need to cut emissions at least by the amount laid out in the current versions of the climate bills before Congress. (The House bill aims to cut emissions by 17 percent by 2020; the Senate version by 20 percent in the same period.

Other rich nations need to follow suit. And then China and other large, developing countries need to jump on the bandwagon within a decade or two.

The scientists explain their "risk assessment" approach:

The scientists use a computer model called the MIT Integrated Global Systems Model. This model is unique in that it couples a climate model with a model of human economic activity and associated energy use.

In May, the same team of scientists released a study saying that "climate change odds" were "much worse than previously thought." Using their probabilistic approach, they found that, without major action, the median probability for warming by 2100 was 5.2 degrees C. That's significantly higher than the "best estimate" in the 2007 report by Intergovernmental Panel on Climate Change: a 4 degree C. increase by century's end if no carbon-curbing action is taken.

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