People cast shadows on the sand as they walk at low tide.
Sand is the building block of megacities around the globe. People use 40 billion tons of it a year. But it's finite. And like oil, controlling it is a deadly endeavor.
Ethiopia's Grand Renaissance dam on the Blue Nile, shown under construction in March of 2014. Egypt claims most of the water in the 4,000 mile-long river that it shares with 10 other countries, and fears the $4.7 billion Renaissance dam will reduce the wa
Not long ago, Egypt all but threatened war if Ethiopia built a huge dam it was planning on part of the Nile River. Now the two countries have signed breakthrough agreement to allow the dam to go ahead. It's a big deal in a region with a history of tension over scarce water resources
A one-horned rhino named Baghekhaity stands next to its 10-day-old calf at a zoo in Guwahati, in the northeastern Indian state of Assam.
What do you do when all other efforts to persuade locals to protect endangered rhinos have failed? Pay them to harvest the rhinos' dung and use it to make paper. That's what an Indian startup company is trying, with early success.
A man takes a shower as policemen patrol during an operation in Rio de Janeiro's Mare slums complex on March 30, 2014.
Brazilians are notoriously lavish bathers, taking as many as three showers a day. But as the country faces a major drought, they're trying to find way to keep up the shower numbers while still saving water.
Protesters march through São Paulo recently demanding equitable distribution of water throughout São Paulo state. Unofficial rationing has brought frequent water outages to neighborhoods throughout the Brazilian megalopolis of 20 million people.
The unprecedented water crisis in South America's largest city is leading citizens to change everything, from how they use water to how they engage with politics. But while the government is taking action, residents say it's not nearly enough.
A worker fills a water tanker for distribution to a hospital in São Paulo in February. Residents throughout the metropolitan region of 20 million people are taking emergency measures amid a severe drought.
São Paulo is facing an unprecedented water crisis that many saw coming, but no one did much to prevent. And with reservoirs hovering near 10% of capacity, many residents are turning to unhealthy stopgaps and worrying about unrest.
The polar jet stream carries weather around the Northern Hemisphere. Climate researcher Jenifer Francis believes the rapidly warming Arctic is slowing and warping the jet stream, allowing Arctic air to spill farther south in some places.
There may be a counterintuitive explanation for the deep freeze that hit New England this winter: The rapidly warming Arctic is causing big disruptions in the jet stream, which carries weather across North America. Is this the worst winter you've experienced?
Local residents wade into the shallow waters of Lake Nicaragua, the largest in Central America, with the volcanic island of Ometepe in the distance. Many are worried that the lake will be contaminated by the country's new $50 billion Chinese-backed Pacifi
China's $50 billion plan for a new Central American canal connecting Atlantic and Pacific may damage the freshwater Lake Nicaragua, changing the environment for those who depend upon it. The plan faces opposition in parts of the country.
Some of the nearly 250,000 Malawians displaced by recent flooding in the southern part of the country sit for a photo at a school where they've taken refuge. Far from the epicenter of international flood relief efforts, the 4,220 people in this isolated c
Massive flooding in Malawi have forced nearly a quarter-million people from their homes, and many say they will never go home. Where will they go?
"Spring is coming" — A pedestrian walks past a pile of snow in Boston.
Global temperatures are going up but that doesn't necessarily mean less snow. Here's a brief explainer of what seems like a contradiction.

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