DURBAN, South Africa—Major industrial and emerging economies set a course to reduce greenhouse-gas emissions over the next decade and beyond, breaking a logjam between China, India and the U.S. that has stymied international climate talks.

Following negotiations that stretched past dawn on Sunday, two days after the two-week United Nations-sponsored meeting was scheduled to end, delegates from almost 200 countries agreed to draft a new global emissions treaty by 2015.

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