PC World: Greenpeace has charged that Facebook, Apple, Microsoft, Google and others are contributing to global warming by using coal to power data centers for their cloud-based services. The charges are dramatic — but are they on target? A new Greenpeace report, titled "Make IT Green: Cloud Computing and its Contribution to Climate Change," warns that the data centers of cloud computing giants including Google, Facebook, Microsoft, Yahoo, and others are in large part powered by coal, which …