Thomson Reuters Foundation/Lin Taylor

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Zero Carbon Cities

More than 70 cities worldwide have pledged to become "carbon neutral" by 2050, meaning they will produce no more climate-changing emissions than they can offset, such as by planting carbon-absorbing trees. Each is going about achieving the goal in its own way.

But because cities account for about three-quarters of the world's carbon dioxide emissions, whether they succeed or fail will have a huge impact on whether the world's climate goals are met.