CANCÚN, MEXICO — During a two-week summit, which ends December 10, negotiators and world leaders will again try to hammer out agreements on climate change, carbon emission reductions, adaptation and mitigation. Tagged “COP 16,” the meetings are the 16th annual Conference of the Parties of the United Nations Framework Convention on Climate Change. In welcoming participants to his country, President Felipe Calderón Hinojosa said, “Putting a stop to climate change is a true challenge, and there is only one power to rise to this challenge: The power of humanity itself.”