Economists have developed theoretical tools for evaluating these incommensurate costs and benefits. But the magnitude of the costs and benefits is less important than their distribution. The gains are diffuse and spread around the world, whereas the pain is intense and local. Economists say that the transactions in such cases have externalities: spillovers on parties who are otherwise not involved. The side effects can be positive; some Mindoro villagers are using the semi-legally cleared land to plant bigger gardens. But the worry is negative externalities: erosion, landslides, yellow sand.
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