Reuters: U.S. President Barack Obama said on Thursday the United States would “lead by example” in combating climate change so that developing nations such as India and China would follow suit. Speaking at the G20 meeting of major economies, he used his presidential debut on the world stage to contrast his policies with those of former President George W. Bush, who had twinned U.S. action to curb climate greenhouse gases with pressure on emerging economic powerhouses. “China and India …