RIO DE JANEIRO — Burdened by low expectations, snarled by endless traffic congestion and shunned by President Obama, the United Nations Conference on Sustainable Development ended as it began, under a shroud of withering criticism.

The anti-poverty organization CARE called the meeting "nothing more than a political charade," and Greenpeace said the gathering was "a failure of epic proportions."

The Pew Environment Group was slightly more charitable. "It would be a mistake to call Rio a failure," the group said, "but for a once-in-a-decade meeting with so much at stake, it was a far cry from a success."

But while the summit meeting's 283-paragraph agreement, called "The Future We Want," lacks enforceable commitments on climate change and other global challenges, the outcome reflects big power shifts around the world. These include a new assertiveness by developing nations in international forums and the growing capacity of grass roots organizations and corporations to mold effective environmental action without the blessing of governments.

The Obama administration offered no grand public gestures here, opting to focus on smaller-scale development projects like clean cookstoves and local energy projects.

Europe, traditionally the driving force behind environmental action yet distracted now by efforts to contain a financial crisis, was considerably more active than the U.S., taking part in nearly every corner of the sprawling conference, called Rio(PLUS)20 to commemorate the anniversary of the first Earth Summit held here in 1992.

The sheer size of the gathering — nearly 50,000 participants including more than 100 heads of state or government — may have raised expectations, in spite of the mixed record of previous such gatherings. The first Rio summit produced two landmark treaties, on climate change and biodiversity, that have so far failed to live up to their promises.

Yet despite this record, the activity outside the main negotiating sessions here produced hundreds of side agreements that do not require ratification or direct financing by governments and that offer the promise of incremental but real progress.

For instance, Microsoft said it would roll out an internal carbon fee on its operations in more than 100 countries, part of a plan to go carbon-neutral by 2030. The Italian oil giant Eni said it would reduce its flaring of natural gas. Femsa, a Latin American soft-drink bottler, said it would obtain 85 percent of its energy needs in Mexico from renewable sources.