Amsterdam, Zagreb, Paris and Mexico City become the first cities to pledge to cut their carbon emissions by 10% in the next year Mexico City's taxis and Paris's city halls are about to become greener after four worldwide capitals signed up to the 10:10 climate campaign. The 10:10 campaign, supported by the Guardian, is championed in 40 countries with 3,000 businesses and 100,000 individuals signing up, including celebrities Sienna Miller and Hugh Fearnley-Whittingstall This is the first time that capital cities have signed up, said campaigners. Speaking from the H�tel de Ville, Paris mayor, Bertrand Delano�, said: "10:10 is an invitation to act concretely and determinedly. I am very happy about this partnership." Social housing complexes will be renovated, head offices of the 20 arrondissements given energy-saving refurbishments and the city's fleet of public vehicles will be "rationalised" in an attempt to cut carbon emissions. Plans have also been unveiled for geothermal wells in the north-east of the city which will power 12,000 homes. The formal agreement from Paris came just before a separate day of international mass participation climate action on 10/10/10, when 7,000 events took place around the world. Twenty four hours later, Paris was joined by the largest city in the Americas, as Mexico City signed the pledge. Its carbon-cutting programme includes the opening of a new line of its Metrobus system (saving 35,000 tonnes of carbon dioxide), replacing all the city's taxis (saving 100,000 tonnes of CO2), building more sustainable homes and large-scale water-saving methane-capture programmes. "It's about the survival of our civilisation," said mayor, Marcelo Ebrard, as he appealed to the city's 21.2 million residents to use less electricity and water and make more journeys by bicycle and public transport. The city's average temperature had risen by 3?C in the previous century, he said. Meanwhile, one million people tuned in to watch Dutch celebrities quizzed on their environmental knowledge on a 10:10-themed television show. It followed Amsterdam's decision to join the campaign, where viewers were given the number of a hotline to sign up to 10:10 over the telephone. Staff in public buildings in the city are already using energy monitors, lights are being turned off when not in use, and thermostats have been turned down. Zagreb would also soon be joining the movement, confirmed the mayor, Milan Bandi?, speaking in the Croatian capital. 10:10 now has hubs in 45 countries worldwide, and in May, the prime minister, David Cameron committed the UK government estate to cutting its emissions by 10%. Ben Margolis, global strategy director at 10:10, said: "This fantastic commitment from four very different capital cities shows how local 10:10 campaigns around the world have grown in strength and confidence."