At the intersection of the "digitalization" and the "climatization" of the agricultural sector grows a promise of the "decarbonization" of agriculture by "start-ups." Based on a qualitative study (40 interviews, 9 days of observation, documentary analysis), this article is a contribution to the political sociology of this promise of ecologization by reconstructing its meaning (what does it signify?) and its implementation (what practices is it referring to?). The study analyzes the bases of a narrative allying the political agendas of agricultural leadership and the executive branch of the French state. The focus on soil CO 2 sequestration and the politicization of innovative "start-ups" converge on the promotion of economic solutions to global warming. The authors found the "start-ups" working on this "decarbonization" were quite diverse, but could be sorted into three types: innovative businesses seeking rapid growth, consultancy firms offering expertise without aims of growth, and administrative intermediaries. The latter, the most numerous and the least innovative, are invested in voluntary carbon markets, most commonly the "low-carbon label," a public framework overseen by the Ministry of Ecological Transition. The promise of the decarbonization of agriculture through start-ups thus falls short, as the study documents an optional and partial greening of agriculture that is overseen by the state, implemented by private administrative service providers, and funded by businesses wishing to improve their carbon footprint.