The world has produced 9.1 billion tons of plastic since 1950. It virtually lasts forever.

$ 4 per person in cities across the globe invested in tree planting could have major benefits, a study finds.

The water crisis in Flint, Mich., has prompted many communities to ramp up testing for lead.

Just as the growth in population makes clean water more precious, it also makes it more expensive.

City trees have huge health benefits. So why aren’t we planting more?

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