Some 3,000 local and regional leaders met in Mexico City to discuss challenges facing cities and towns across the world, from economic and social woes to climate change.

Mexico City mayor Marcelo Ebrard and Paris Mayor Bertrand Delanoe, the current president of the United Cities and Local Governments, were among those opening the summit, set to last four days in one of the world’s largest and most polluted cities.

Around 70 mayors, from cities from Barcelona to Buenos Aires, yesterday signed a voluntary pact in Mexico City to reduce greenhouse gas emissions, as well as 30 others who will not be present, authorities said.

The document will be presented to a UN worldwide climate conference in the Mexican beach resort of Cancun to be held from November 29 to December 10.

“We have to tell the international community that it’s in the cities that the battle to slow global warming will be won,” Dr Ebrard said.

Mexico City lastweek promised to reduce its annual greenhouse gas emissions by around 14 per cent.