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World lead­ers who de­scend­ed on the Unit­ed Na­tions an­nu­al cli­mate sum­mit in Brazil on Thurs­day on­ly need­ed to look out their air­plane win­dows to sense the un­fath­omable stakes.

Sur­round­ing the coastal city of Belem is an emer­ald green car­pet fes­tooned with wind­ing rivers. But the view al­so re­veals bar­ren plains: Some 17% of the Ama­zon’s for­est cov­er has van­ished in the past 50 years, swal­lowed up for farm­land, log­ging and min­ing.

Known as the “lungs of the world” for its ca­pac­i­ty to ab­sorb vast quan­ti­ties of car­bon diox­ide, a green­house gas that warms the plan­et, the bio­di­verse Ama­zon rain­for­est has been choked by wild­fires and cleared by cat­tle ranch­ing.