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The use of aborted fetal tissue has sparked controversy in the United States, but many scientists say it is essential for studies of HIV, development and more.
After 25 years of negotiations, all countries are finally set to take steps to limit global warming. A special issue examines the path to the Paris climate summit, and the road beyond.
Many physicists believe that entanglement is the essence of quantum weirdness — and some now suspect that it may also be the essence of space-time geometry.
The island nation of Kiribati is one of the world's most vulnerable to rising sea levels. But residents may have to leave well before the ocean claims their homes.
As a massive El Niño warming builds in the equatorial Pacific Ocean, researchers hope to make the most of their chance to study this havoc-wreaking phenomenon.