The stupidest debate in climate negotiations?

In 2009 there was, seriously (hell, there probably still is) a debate over whether we should stick with 1990 as an index year for emissions cut promises, or change to 2005 as an index year.

This is a deeply stupid debate. The climate change problem is an absolute problem. To fix it, you have to reduce the amount of carbon (equivalents) going into the atmosphere by an absolute amount. The only thing changing the index year does is affect how impressive your cut sounds. Saying "we'll target emissions 20% lower than 2005!" sounds a lot better than saying "we'll target emissions 5% lower than 1990!" But the effect on the atmosphere is exactly the same. A given pledge translates to a given absolute number of tons of carbon going into the atmosphere, which gets you a given amount of the way toward where we need to be to not all collapse in a crazy-weather apocalypse. The index year is fundamentally window-dressing - just shorthand for "how many tons of carbon we were each emitting at an arbitrary point."

The question of why governments do this kind of thing in negotiations (argue over what amount to cosmetics, when both sides are clearly fully capable of doing the underlying math) and whether it makes any real difference is actually a going concern amongst those who study international relations. It seems clear to me that in this case the point is largely to confuse the issue ("20%? Are they talking relative to 1990 or is this one of those new 2005 pledges?") and hope it creates a PR win for you ("20%? Gosh, that's just as much as those climate hawk Europeans are promising!" The European pledge being a 1990 pledge, of course.)