In the first international test for his climate-change strategy, President Barack Obama pressed world leaders Tuesday to follow the United States' lead on the issue, even as a United Nations summit revealed the many obstacles that still stand in the way of wider agreements to reduce heat-trapping pollution.
"The United States has made ambitious investments in clean energy and ambitious reductions in our carbon emissions," Obama said. "Today I call on all countries to join us, not next year or the year after that, but right now. Because no nation can meet this global threat alone."
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