U.S. President Barack Obama says the task ahead for representatives from more than 150 countries to achieve a deal to address climate change is not easy, but he's optimistic it can happen.
Facing political opposition from some Republicans at home, President Obama also underscored that there is global consensus - both from officials and researchers - that the climate is changing and the next president of the United States must take the issue very seriously.
President Obama thinks big things can get done in Paris - where the talks will continue over the coming two weeks.
IN: "We will...
OUT: ...climate change."
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