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By Sadhbh O’Neill.

In 2009, signatories to the UNFCCC met to agree new legally binding greenhouse-gas emission targets. The outcome, known as the Copenhagen Accord, singularly failed to meet high expectations for a legally-binding agreement but the Accord did specify for the first time that the objective of the international community was to “hold the increase in global temperature below 2 degrees Celsius”.

In the lead-up to the next big opportunity for a global climate agreement in Paris this December (COP-21), 2 degrees is repeatedly used as a reference point to frame a political deal. The 2 degree warming limit is essentially a political construct with a scientific basis for climate policy – but it is a tragically flawed approach.

In principle, the 2 degree threshold made sense back in 2009: it seemed to be a politically realistic target but the politics changed as it became clear that change would be too slow, and – even more importantly – the received science changed too.

As recently as 2007, scientists reasoned that CO2 concentrations could be safely allowed to reach 550 parts per million (ppm),  but more recent research produces a scientific consensus that “urges the world to reduce atmospheric carbon dioxide concentration CO2 to about 300 ppm by volume” to keep below 2 degrees warming. But crucially and shockingly it is already over 400 parts per million. The National Geographic noted that the concentration of carbon dioxide in the atmosphere is this high “for the first time in 55 years of measurement – and probably more than 3 million [others say 20 million] years of Earth history”.

In any event, the risks associated with even 2 degrees of warming have been vastly underestimated. The likes of former NASA climate scientist James Hansen are now saying that even 1 degree is not safe. Tyndall Centre scientists Kevin Anderson and Alice Bows-Larkin stated as far back as 2011 that the latest evidence suggested that 2 degrees “…now represents a threshold, not between acceptable and dangerous climate change, but between dangerous and ‘extremely dangerous’ climate change: in which the importance of low probabilities of exceeding 2 degrees Celsius increases substantially”.

The scientists argued that any assessment of climate policies should be framed in light of the likelihood of adhering to an emissions pathway that would stick to the 2-degree carbon budget. Yet they found that many of the models used to map out emissions-reductions scenarios showed that there was in fact a high probability of the 2-degree warming threshold being breached.

For one thing, the global climate regime requires an acceptance of a global carbon budget instead of future-oriented mitigation targets. It is cumulative global emissions that count; not just good intentions to reduce emissions in the future. According to one recent publication [Brad Plumer ‘2 degrees: How the world failed on climate change’ Vox, 22nd April 2014], one tenth of the total carbon budget allowable under a 2-degree warming scenario was emitted in 2012 alone. Moreover emissions are still rising: the only year since the base year of 1990 to report a global emissions reduction is 2008, when economies around the world ground to a halt in the grip of a global recession. That decrease only amounted to 1% and only for one year. Overall, since 1990 global emissions have risen by 57%  and show no signs of abating. Even the IPCC has warned that the narrow window of opportunity to take action on reducing emissions gradually has probably passed, and effective measures will now require drastic and sustained cuts by Annex I [ie rich] countries.

In 2011 and in more recent papers, Tyndall Centre scientists Kevin Anderson and Alice Bows-Larkin have looked at the realistic emission pathways required both to meet a 2-degree warming limit and fairly share the carbon budget between Annex I and non-Annex I countries, and conclude that developed nations are likely, based on ‘business as usual’ scenarios, to use up the remaining budget since they are ‘locked-in’ to fossil fuel and growth-dependent economies. Furthermore, the various emission pathway scenarios developed by Annex I countries to project a peak to their emissions and then reduce them whilst adapting to already-embedded climate change do not adequately assess the risks and probabilities of reaching or exceeding the 2-degree warming target.

If the international community is serious about backing up any limit to global warming with credible but fair policies, then scenarios will have to be developed that explicitly construct pathways for developing countries to grow, peak and then reduce their emissions, alongside radical cuts in emissions by Annex I countries. But effective climate policies need to be measured against scientific evidence and their likelihood of succeeding: not against wishful or magical thinking. •