Having outlined a theory of heterogeneous social construction, this article describes the scientific construction of climate change as a global-scale environmental problem caused by the universal physical properties of greenhouse gases. Critics have noted that this reductionist formulation serves a variety of political purposes, but instrumental and interest-based critiques of the use of scientific knowledge tend to ignore the ways in which a politics gets built into science at the upstream end. By retracing the history of climate modeling and of several scientific controversies, I unmask the tacit social and epistemic commitments implied by its specific practices. The specific scientific framing of global climate change has reinforced and been reinforced by the technocratic inclinations of global climate management. The social organization of climate change science and its articulation with the political process raise important questions about trust, uncertainty, and expertise. The article concludes with a discussion of the political brittleness of this dominant science-led and global-scale formulation of the climate change problem and the need for a more reflexive politics of climate change and of scientific knowledge based on active trust.