Xinhua: A group of activists from Greenpeace Mexico set on Wednesday a billboard addressed to Mexican President Felipe Calderon and U.S. President Barack Obama, urging them to take measures against the climate change. The billboard read “Save the climate, act now,” with pictures of Calderon and Obama. It was placed in front of the Monument to the Revolution in Mexico City. Obama will arrive in the city on Thursday for a two-day visit in Mexico, before attending the 5th Summit of the …