Bloomberg: Cities are the world’s biggest source of carbon emissions and must embrace technology to clean the air and counter global warming, Hong Kong Chief Executive Donald Tsang said. “Cities must unlock the full potential of low carbon technologies,” Tsang said at the opening of a two-day climate- change forum that includes the mayors of Toronto, New York City and Johannesburg. A woman unfurled a Greenpeace banner with an anti-nuclear slogan during Tsang’s speech and was led away without struggle by…