Mexico City's Mayor Marcelo Ebrard said Friday in Rio de Janeiro that global sustainability will depend on actions taken at cities around the world.

Ebrard made the remarks at a press conference held on the last day of the UN Conference on Sustainable Development (Rio+20), joining leaders from the public and private sector to highlight some of the voluntary commitments made during the summit.

The mayor said that in recent years cities have emerged as a strategic player for confronting the consequences of global warming and so far 242 cities from 54 different countries have joined the Mexico City Pact (MCP) to fight global warming.

Each city has committed to reduce its polluting emissions and their advances are measured each year by Carbon Foundation.

"Probably measuring yearly the advances of the cities on their reduction of polluting emissions may not sound practical, but if we don't do it, everything would sound very beautiful in the speeches, but nothing would be set on march," he explained.

According to the International Energy Agency, cities use 67 percent of the world's energy and generate more than 70 percent of CO2 emissions.

The MCP includes cities like Bangkok, Barcelona, Bogota, Bordeaux, Brusseles, Buenos Aires, Caracas, Kyoto, Los Angeles, Mexico City, Santiago, Paris, Rio de Janeiro and Tokyo.