President Obama (from left), French President Francois Hollande and Microsoft co-founder Bill Gates applaud a speech during the Mission Innovation event at the UN conference on climate change Monday in Paris.
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A building called Sustainability Base, at NASA's Ames Research Center in Mountain View, Calif., has an energy-efficient design that allows in sunlight. So for most of the year, the interior is illuminated by natural light.
A view of the opening of COP21 on climate change Monday in Paris. More than 150 world leaders are meeting for the 21st Session of the Conference of Parties to the United Nations Framework Convention on Climate Change.
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A power-generating windmill turbine is seen in front of the Arc de Triomphe on the Champs Elysees avenue in Paris ahead of the COP21 World Climate Summit, which begins Monday.
Christian Hartmann/Reuters /Landov
Delegates from about 170 countries gathered in Kyoto in December 1997 during the United Nations Framework Convention on Climate Change. This year in Paris, the stakes are even higher, negotiators say.