When I hear discussions about creating markets to “save nature,” a part of me is hopeful, but a bigger part is deeply cautious. Looking at how these market ideas have played out, like carbon markets, gives me pause. Forests, wetlands, and the natural world are not simple spreadsheets; treating them as such can lead us down a perilous path… Carbon, as CO2, is a global pollutant. A tonne reduced in one place has, theoretically, the same atmospheric impact as a tonne reduced elsewhere.This (imperfect) fungibility is what would allow a global carbon market to function. Biodiversity, however, is the epitome of diversity, local and unique. The specific mix of species, the genetic diversity and the intricate ecological relationships that define a patch of old-growth rainforest in the Amazon are utterly different from those in a Scottish pine forest or an Indonesian mangrove. You cannot swap one for the other and claim equivalence.