Many recent papers highlight the importance of thinking about carbon emissions (CO2e) in machine learning (ML) workloads. While elevating the discussion, some early work was also based on incomplete information. (Unfortunately, the most widely cited quantitative estimate that was the basis for many of these papers was off by 88X.) Inspired by these concerns, we looked for approaches that would make ML training considerably less carbon intensive. We identified four best practices that dramatically reduce carbon emissions, and demonstrate two concrete examples of reducing CO2e by 650X over four years and 40X over one year by following them. Provided ML stakeholders follow best practices, we predict that the field will bend the curve of carbon footprint increases from ML training runs to first flatten and then reduce it by 2030 without sacrificing the current rate of rapid advances in ML, contrary to prior dire warnings that ML CO2e will soar.