In the 1980s climate scientists and ecologists began to study the relationship between forests, particularly the Brazilian rainforest, and anthropogenic climate change. This paper identifies how these scientists developed two contrasting models to highlight the bioclimatic value of rainforests: the air-conditioner and the sink. Whereas climate scientists largely highlighted the role of the Amazon in ensuring cool temperatures and frequent precipitation (an air conditioner), ecologists focused on the role of the Amazon in sequestering carbon (a carbon sink). Although frequently aligning with the rainforest biodiversity movement, these bioclimatic valuations of the rainforest sometimes contrasted in both means and ultimate goals. Indeed, the ability of models of carbon sinks to simplify and quantify the diverse rainforest environment allowed for the development of a global carbon offset market by the mid-1990s. This paper seeks to understand this shift, analyzing why carbon sequestration quickly became one of the largest drivers of land conservation in the tropics.