Reuters: More than 20 U.S. cities, including New York, Las Vegas and Denver, have agreed to measure their carbon footprints, with a system some 1,300 companies have been persuaded to use, in an attempt to find ways to curb emissions blamed for warming the planet. “If you don’t measure these emissions, you cannot manage them,” said Paul Dickinson, the chief executive of the UK- based Carbon Disclosure Project, which joined forces with the cities. Urban traffic, buildings and manufacturers emit …