Only time will tell whether the deal struck in Copenhagen proves a true turning point in the effort against climate change.  Flying home after two chaotic and exhausting weeks, I find I’m of two minds.

The deadline of December 18, 2009, in fact drove many governments further than before.  In the weeks preceding, the United States, China, India and others felt compelled to come forward with explicit emission pledges.  Under the Copenhagen Accord, countries have until January 31 to put these numbers on record; then there is no taking them back.

These pledges are not binding.  They are statements of intent, not obligation.  But that is not what disappoints me.  I never expected Copenhagen to produce more than a political accord.

What troubles me is that governments did not resolve to move next to a legally binding treaty.  That goal was part of the tentative agreement announced by President Obama.  But then he left, and in final deal-making, it somehow vanished.  The negotiations will of course continue.  Governments agreed they’d meet next year in Mexico, the year after in South Africa.  But with what type of agreement in mind?  That’s unclear.

Is a treaty necessary?  After all, it is domestic law that directly conditions the choices of producers and consumers.  That is why comprehensive federal climate legislation is so absolutely critical.  But for a country to maintain its strongest possible effort, it must be confident that others are too.  And I’ve always been of the belief that this confidence is best instilled by mutual and binding commitments – a contract among nations.  Are we to believe that in the face of perhaps history’s most profound global challenge there is no role for international law?

Perhaps a global treaty is a quixotic notion.  Perhaps the best that can be mustered are political agreements.  Perhaps it is time to reform the U.N. process, or to move outside it to build coalitions of the willing.  These are questions worth pondering.

But the more immediate measure of Copenhagen is whether it gives countries enough confidence to go the next step domestically.  I believe it should.

In addition to individual pledges of action from all the major economies – including the first ever from China and other big developing countries – the accord sets out initial terms for verifying those actions.  This was a principal objective of the United States, and a clear concession on the part of China.  It offers the promise, once the details are agreed, of some level of international accountability.  With that, there is now one less excuse for Congress to avoid acting.

That Copenhagen did not achieve more is in many ways understandable.  President Obama brought to the table all he reasonably could at this stage.  But with Congress not having yet acted, the United States wasn’t in a position to put its best offers on the table. So there was no reason to expect that other governments would either.

But it is an advance, one we must seize on.  Congress needs to get on with the job of legislating.  And when it is done, perhaps we can then revive the goal of a legally binding treaty.