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Is 1.5 degrees a scientifically realistic target?

  • 13 Jun 2011, 17:00
  • Christian

We are currently half way through an interim meeting of the UN's Framework Convention on Climate Change (UNFCCC), the body that is supposed to be negotiating a sensible global climate deal. And once again, the disconnect between scientific and political reality is startlingly apparent.

As the world struggles towards some sort of agreement, the discussion about what shape a deal should take - and even what it should be aiming for - continues. The Copenhagen Accord [pdf], which the UNFCCC agreed to 'take note of' at the end of 2009, recognized

"the scientific view that the increase in global temperature should be below 2 degrees Celsius".

But at the beginning of last week, the executive secretary of the UNFCCC, Christina Figueres, went on the record saying

"Two degrees is not enough - we should be thinking of 1.5C. If we are not headed to 1.5C we are in big, big trouble."

Small island states - aware that their survival is threatened by climate change - have made repeated calls in the negotiations for the world to commit to keeping temperatures to 1.5 degrees above pre-industrial level. But their call has largely fallen on deaf ears.

This is perhaps unsurprising given that its taken 20 years to get the world to commit to two degrees as a target, even in principle. But it is worth pointing out how far away from the current scientific reality the 1.5 degree target is. 

Figueres' statement coincided with an IEA assessment that global emissions from the power sector are at an all-time high - as assessment which suggests that if current trends in emissions continue, a four degree rise by the end of this century looks likely.

A recent policy briefing from the Grantham institute and the Met Office detailed the challenges implicit in a 1.5 degree target, concluding that temperatures will now almost inevitably rise above 1.5 degrees. The best we can hope for, they suggest, is that with rapid emissions cuts it may be possible to end up with temperatures less than 1.5 degrees above pre-industrial - but only if temperatures 'peak and decline' following rapid cuts in emissions.

To have a more than 50% chance of achieving this, the report suggested immediate and very rapid emissions cuts would be necessary. The authors however note that

'The feasibility of such rapid rates of emissions reductions is an area of active debate.'

There are also large scientific uncertainties about the feasibility of whether it is possible to 'overshoot' on temperature rise - possibly for up to 100 years - and then bring temperatures down again.

Without putting too much weight on one study, this kind of essentially fairly simple budgeting analysis shows that two degrees is in danger of becoming a 'best case' scenario, rather than the 'must not be crossed' limit it still occupies in much of the discussion on this issue.

And that raises some pretty fundamental questions about the framing of a lot of current climate geopolitics from politicians and advocates. It may be that a fixation on 2 degrees and less is in danger of missing the increasingly obvious - that staying under even that limit already requires a great deal of extra ambition and delivery on emissions cuts, as well as a modicum of luck. Despite the fervent wishes of diplomats, activists and affected people around the world, the basic science of climate change isn't going to change anytime soon.

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