Former New York Mayor Michael Bloomberg thinks cities are a crucial element in the fight against climate change.
Bloomberg, now a U.N. climate ambassador, said cities are the key because they make up 75 percent of the heat-trapping gases, and mayors have executive powers to reduce emissions.
During his keynote speech, Bloomberg called on cities to act expeditiously in curbing greenhouse gas emissions.
"Those actions will save lives; they'll strengthen and protect the national economies; they'll make cities more healthy and economically vibrant, and together, they'll make a difference in the global fight against climate change," Bloomberg said.
His comments come less than a week before President Obama is set to unveil a cornerstone of his climate agenda, the first rule aimed at limiting carbon emissions from existing coal-fired power plants.