Reuters: The United States should show decisive leadership at the Group of 20 summit in Pittsburgh this month and rally heads of state to prepare for the next global crisis — climate change. In a speech before the G20 meeting on September 24-25, Nancy Birdsall, president of the Washington-based Center for Global Development, said preparing for climate change was key because it was a new issue and because the world’s poor will be severely hurt by it. Influential think tanks in …