Setting limits on greenhouse gases is fraught with difficulty—each country has their own horse in the race, their own interests at stake. Agreeing to an emissions cap would seem to be the first obstacle delaying international climate policy. If the issue were settled, countries could move on to debate mechanisms, penalties, and assistance programs. But even before emissions caps can be set, another technicality stands in the way—the year on which emissions targets should be based.
The internationally accepted baseline year is 1990. The year has been nearly ubiquitous in climate change negotiations and the scientific literature. But fast forward fifteen years and another baseline year has emerged—2005. Didn’t we already agree to a target year?
It turns out that 1990 emissions levels have become increasingly difficult to reach in those fifteen years. In that time, global greenhouse gas emissions increased 28 percent (pdf), and U.S. emissions increased 16 percent. Larger sounding but more politically convenient targets are easier to obtain using 2005 levels. So President Obama’s proposed 17 percent reduction below 2005 levels by 2020 only amounts to a cut of 3.7 percent below 1990 levels. By contrast, the European Union has put a 20 percent cut below 1990 levels by 2020 on the table, which it would raise another 10 percent if an international agreement could be reached. To match that, U.S. would have to drop emissions 31 percent below 1990 levels and add another 9 percent in the face of international consensus.
That the U.S. is proposing cuts in emissions at all is a step toward reaching an international agreement. But the continued use of 2005 as a baseline only muddies the waters, making proposed emissions targets difficult to compare.