44 Gt figure misses the point, the turn is key

The lead-up to Copenhagen has seen a welcome flurry of target announcements. President Barack Obama has promised emissions reductions "in the range of 17% below 2005 levels in 2020," in line with the climate bill that has passed the U.S. House and is now in the Senate. China, India and others have followed suit. Opinions differ how these targets stack up.

UNEP yesterday presented a report by Lord Stern that says countries "may be closer than some observers realise to agreeing the emissions cuts required to give the world a reasonable chance of avoiding global warming of more than 2˚C." The report shows that current proposals add up to 46 Gt (billion tonnes aka gigatonnes) in 2020. A 50/50 chance of avoiding warming above 2˚C would require 44 Gt. We are only off by 2 Gt, or so UNEP says.

There is some debate around the numbers. An earlier, independent analysis by Project Catalyst says we would miss the mark by 6 Gt or more. Our own analysis shows that proposals on the table add up to 48 Gt, 4 more than the 44 Gt figure.

The drive to get concrete figures is understandable. We need to know where the negotiations stand. All of these accounting exercises, however, miss three crucial points:

  1. Large uncertainties around business-as-usual (BAU) projections make predictions within 1, 2 or even more Gt extremely difficult. It cannot give us confidence that 44, 46, or 48 are accurate to the nearest Gt. What it does show is the importance of tying targets to historical baselines rather than diversions from BAU.
  2. Traditional imprecision associated with climate models renders hard thresholds, like the 44 Gt figure, difficult to defend. First, a coin toss's 50/50 chance of avoiding warming above 2˚C is simply not good enough. Second, this is one possible pathway to 2˚C. There are many others, some known as "peaking" pathways allow as much as 46 or 48 Gt by 2020, assuming steeper decreases after the peak.
  3. The trajectory is more important than year-by-year emissions. Current offers on the table may meet the 2020 Gt requirements, but they don't lead to a global peak before 2040. The world needs to peak by around 2020 or shortly thereafter. By 2040, the gap between what's on the table now and where we need to be is greater than 25 Gt. Emissions would be more than twice where they should be! The most important part is not to stabilize emissions by 2020, it's to get on a rapid downward slope soon, decreasing emissions at a rate of around 4% per year shortly after the peak.

Let's avoid the 44 Gt chorus and the guessing about whether we are off by 2, 4 or 6 Gt. Instead, let's focus on the turning point of global emissions, the percentage decrease in emissions after the peak, and the long-term prospects for climate stability. The key is to start the turn toward climate safety now.

Turn toward climate safety

Turn toward climate safety

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