Machine Learning (ML) workloads have rapidly grown in importance, but raised concerns about their carbon footprint. We show four best practices to reduce ML training energy by up to 100x and CO2 emissions up to 1000x, and that recent papers overestimated the cost and carbon footprint of ML training by 100x–100,000x. Finally, we show that by following best practices, overall ML energy use (across research, development, and production) held steady at <15% of Google’s total energy use for the past three years. If the whole ML field adopts best practices, we predict that by 2030 total carbon emissions from training will reduce.