U.N. Secretary-General Ban Ki-moon addresses the opening of the high-level segment of the annual U.N. climate talks involving environment ministers and climate officials from nearly 200 countries, in Doha, Qatar, Tuesday, Dec. 4, 2012. Ban has urged governments to speed up slow-moving talks to forge a joint response to global warming and warned that climate change was an "existential challenge for the whole human race." (AP Photo/Osama Faisal)
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