Global carbon markets will struggle after the deal reached at annual U.N. climate talks did little to ensure mandatory emissions caps would be extended next year.

The modest deal forged after two weeks of talks in Cancun commits rich countries, from 2020, to finance $100 billion a year in climate aid for poor countries. It also sets a target to limit the rise in average world temperatures to less than 3.6 degrees Fahrenheit.

But it delayed the difficult task of extending the 1997 Kyoto Protocol until next year’s talks. Japan, Canada and Russia said they would not support a second phase of Kyoto if it did not include caps on the United States and rapidly developing countries like China.

Kyoto, which expires in 2012, obliges all developed countries — except the United States, which never ratified it — to cut emissions or face penalties.

“The outcome of Cancun does not change the fact that most of the important work of cutting emissions will be driven outside the U.N. process,” said Michael Levi of the Council on Foreign Relations in New York.