For the past few years, I have tried to see the results of the COP meetings in Copenhagen, Cancun, and Durban through a “glass-half-full lens,” arguing that even weak agreements keep the process going.

Now that COP17 is in the books with an apparent agreement to work toward a globally binding successor to Kyoto, some might argue that the intergovernmental process can deliver the framework needed to reverse climate change.

But I came away from the events more pessimistic than usual, and the reasons have far more to do with events in Brussels than in Durban.

Let’s assume that in 2015 the world’s governments sign up for a globally binding successor to Kyoto that takes effect no later than 2020. Why should we have any faith that behavior will change?

Here is where the experience of the eurozone is instructive. As Europe tries to negotiate out of its sovereign debt crisis, let’s remember that the eurozone countries had already committed themselves to maintain debt levels at no more than 3 percent of gross domestic product (GDP). For nearly a decade, many countries, including the two eurozone countries that matter most, Germany and France, have breached that commitment, with no significant means of enforcing the provision.

This situation occurred for two reasons. First, it may well be that debt as a ratio of the GDP was the wrong measure. Second, there has been no enforcement mechanism to bring wayward countries into compliance—mainly due to the lack of corresponding political union to the economic union.

A successor to Kyoto is likely to have the same structural problem, on a much larger scale. There is little reason to believe that national governments will sacrifice their short-term political viability or their nations’ economic vitality to meet the requirements of a global treaty that will have inadequate enforcement mechanisms. This is not the first time that the mismatch between governance structures and global objectives has been apparent: Indeed, the creation of effective global governance for our common aspirations is the central challenge of the 21st century.

The European Union’s commitments to achieve real reductions in carbon emissions have been exemplary. But the EU’s experience in trying to enforce discipline within its own region provides an important example of how a global deal on climate change is necessary, but not sufficient, to tackle the problem.