US grid carbon intensity is 0.384 gCO2/kWh (source: ourworldindata). US datacenter energy use in 2023: 176 TWh (excluding crypto, source US congress). How much of that is AI, I couldn't find.

So that's 67Mt CO2, I hope I haven't misplaced my decimal point, please double check. That would be 1.3% of the 5Gt of CO2 the US emits per year.

https://ourworldindata.org/grapher/carbon-intensity-electric...

https://www.congress.gov/crs-product/R48646#_Toc207199546

For global emission and future trends the IEA estimates about 500TWh/year globally today, and 1000TWh/year in 2030 (base scenario). Assuming these use the current US grid carbon intensity, that would be about 200MtCO2 today, 400 in 2030. Global CO2 emissions today are 40Gt/year, so that would be 0.5% today, and 1% in 2030 (if global emissions stay stable).

https://www.iea.org/data-and-statistics/charts/global-data-c...