Xinhua: The United States is ready to take the lead in the global efforts to tackle climate change, U.S. President Barack Obama said on Sunday, signaling a policy change of Washington. “To protect our planet, now is the time to change the way that we use energy,” he said while addressing a crowd at a square outside the Prague Castle. It was Obama’s first public speech abroad since he took office in January. He is in the Czech Republic for a summit with European Union (EU) leaders on …