Reflections on Copenhagen – 2 degrees the target, but 3.5 more likely

07 Jan 2010 by Peter

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One of the more positive outcomes from the Copenhagen Accord – and let’s face it, we weren’t inundated – was the acknowledgement by both developed and developing nations that increases in global temperature need to limited to no more than 2 degrees by 2100 if we’re to avoid the worse effects of global warming.  See paragraphs 1 and 2 of the Accord for the details.

For those of you not familar with the IPCC complied science, that translates to atmospheric greenhouse gas levels of no more than 450 ppm, which in turn will require a global reduction of around 13Gt of CO2-e  per year by 2020. So if 2 degrees represents the target, how far does the current global response go to achieving it?

The guys at Climate Action Tracker have been busy translating the range of commitments made by the world’s largest carbon polluters into likely scenarios in terms of global CO2 concentrations and associated warming. The news is not great. The two images below, borrowed from the CAT website, demonstrate in simple terms that, based on the most likely current commitments from major industralised and developing nations, we’re on course for warming in the region of 3.5 degrees by 2100.

climate action trackerhp_thermometer

Delving a little deeper, the graph shows annual global GHG emissions out to 2050, with the gray line representing business as usual and the solid black line representing a 450ppm / 2 degree warming scenario.  Finally, the red line shows forecast GHG emissions based on the most likely range of commitments and pledges made by major carbon polluters, including Australia.

The thermometer to the right represents what these commitments translate to in terms of likely global temperature increase by 2100. The higher number relates to the least ambitious of the range of comittments made and conversely the lowest number to the most ambitious. Even under the most abitious reduction scenario currently on the table warming is likely to be in the range of 2.8 degrees.

This all paints a rather bleak picture, particularly when you take things a step further and look at projected sea level rise associated with 3.5 degrees of warming. A recent report, published in the scientific journal Nature and discussed in some detail on the Guardian website, suggests a warming of this magnitude could lead to sea level rise of around 1.5m by 2100 and up to 8m 0r 9m beyond that.

With developed nations due to confirm their final emissions reduction commitments by the end of this month, we’ll have a better idea of just how far off the mark we’re likely to be. One thing is clear though, global climate change politics is no nearer finding a solution that the science demands.

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