I dont know much about what format the data source should be in but there are a lot of resources. Here are a few more from a qick google https://www.kaggle.com/ucsandiego/carbon-dioxide https://www.esrl.noaa.gov/gmd/ccgg/trends/monthly.html https://climate.nasa.gov/vital-signs/carbon-dioxide/