One of the ongoing debates in Poznan is whether to enumerate some kind of goal for emissions reductions, at least in the short term. The usual number that comes up for Annex I countries – the industrialized world – is 25-40 percent below 1990 levels by 2020, and the EU has been pushing for a 50-percent reduction by mid-century in order to limit global warming to 2 degrees Celsius. The scientific basis for this, however, is unclear at best.
The United Kingdom’s Martin Parry, who co-chaired the impacts and adaptation group for the International Panel on Climate Change’s 2007 assessment, reiterated his position that the policymakers are aiming too low. “The 50-percent pathway won’t do what they think it will, and that’s a pity,” Parry said after his presentation this afternoon. “The problem is they are working with old information.”
Parry crunched some numbers before the conference and determined that the odds of staying under 2 degrees of warming are only slightly better than 50/50 even if emissions peak in 2015 and then decrease to 60 percent below 1990 levels by mid-century. (Because the climate takes time to respond to greenhouse gases, the full impact of warming in this scenario does not occur until 2100; Parry addressed this issue in Nature Reports Climate Change in June). If you want to increase the odds of coming in under 2 degrees and avoid the most serious impacts of global warming, you need an 80-percent reduction by 2050.
Individually, some nations are looking at 80-percent figure. The United Kingdom’s climate plan shoots for 80 percent, and US President-Elect has called for 80 percent in his climate plan. But there’s another twist in Parry’s numbers: Each decade that the global peak is delayed, the temperature increase goes up by .4 to .5 degrees. According to this model, an eighty percent reduction by mid-century delivers 1.4 degree of warming with a peak in 2015; 1.8 degrees if the peak is in 2025; and 2.4 degrees with a peak in 2035. In other words, there is a penalty for delayed action.
The 25-40 percent goal is discussed as if it were an IPCC recommendation for limiting atmospheric carbon dioxide levels to 450 parts per million (they are currently around 385 ppm and rising at a rate of around 2 ppm annually). In fact, these numbers were more of an assessment of options, not a recommendation. Almost by extension, the 50-percent cut by mid century is often linked to the IPCC as well, but this story is a bit murkier. Although a group of some 200 climate scientists penned a letter last year calling for cuts of “at least” 50 percent by mid-century, the most recent IPCC report actually gives a range of 80-95 percent by mid century for the 450-ppm scenario.
To be clear, Parry’s model shows substantial climate impacts even under the strictest scenario, and Parry believes policymakers have not even begun to understand the scale of the problem. “The adaptation funding needs to be cranked up measurably, probably an order of magnitude,” he says, suggesting that $1 trillion annually might be a good target. “And the research needs to start now.”