When I interviewed Terry Tamminen about (among other things) California's experience putting together a climate plan, he stressed the importance of putting together a comprehensive inventory of GHG sources:

We had pretty good knowledge of emissions from the utilities sector, but it was poor in terms of the agriculture sector, the cement sector, etc. We had to sharpen our inventory to actually start imposing things and knowing if they work. We're encouraging other states to use some of the technical assets out there in the non-profit and academic world to help them do robust inventories.

Tamminen said he intended to "Johnny Appleseed" the California experience in other states, and at least on this score, it seems to be working, as 31 states just pledged to join a registry that would track emissions. Unlike the federal tracking, this registry would be verified by a third party, so it'll be interesting to see the results.

That's 70% of the U.S. population whose emissions will now be reliably tracked. Not bad.