PARIS (Reuters) - The U.N. climate panel agreed on Thursday it was "very likely" that human activities were the main cause of global warming in the past 50 years, stepping up certainty from a 2001 report, delegates said. The wording "very likely" means at least 90 percent probability by the Intergovernmental Panel on Climate Change, which is meeting in Paris this week and will publish a new report on Friday. The last study, in 2001, said that there was only a "likely" link, or a 66 percent probability, that human activities were the main cause of warming in the past...