The Quagmire of Baseline Years

4 November 2009

Although voices from many quarters in Barcelona are complaining that the US delegation has put no numbers on the table, there is one number that just keeps popping up. That number is 2005, the base year for the US legislation currently on the table.

Even though it was four years ago, 2005 just happens to be the year of the highest US emissions in history. Coincidence?  You be the judge.  But to the point, this proposed base year distorts an important discussion on ‘comparability’ and has become a red herring in assessment of the adequacy of the scale of mitigation targets.

The US delegation often seems to insinuate that 1990 was just an arbitrary base year. Of course, 1990 was not selected at random: it was the year of the IPCC’s First Assessment Report; the year when the world began negotiating what became the Convention.

But arbitrary or not, shifting to a different base year like 2005 allows the US to imply that the EU proposed mitigation target of 20% by 2020 relative to 1990 is about as ambitious as that in the US legislation. In effect, this amounts to suggesting that emissions reductions elsewhere between 1990 and 2005 are irrelevant to negotiations today.  The comparison we really should be making is the distance between the proposals on the table and what the science is saying we have to do.

Many countries including the US failed to begin reducing emissions between 1990 and 2005.  But greenhouse gases cannot simply be written off by changing the base year. They collect and persist in the atmosphere, and all the while carbon sinks have been degraded and lost.

Countries may find it domestically convenient to use a different baseline year, but this presents several problems. Converting reporting data from one country to another appears to be simple enough in theory.  But in practice, measurement, reporting and verification requires comparing apples to apples.  Converting multiple data points across multiple countries using a variety of different baselines is a convenient recipe for confusion and avoiding the big picture (remember? “compare the targets to what the science demands”).  So even if the experts can provide conversion formulas for differing baselines, there is still a question of public transparency and accountability.

And finally, if the baseline changes, so must the targets. Were we to use a 2005 baseline, the IPCC says global emissions should come down 35-50% by 2020 (as opposed to 25-40% with a 1990 baseline). In the context of history and science, using 1990 is not at all arbitrary.