From a theoretical standpoint, virtually any source of carbon could be used, you could even make it out of the carbon already in the atmosphere: https://www.re

From a theoretical standpoint, virtually any source of carbon could be used, you could even make it out of the carbon already in the atmosphere: https://www.reuters.com/article/us-climatechange-carbon/scientists-say-cost-of-sucking-carbon-from-thin-air-could-tumble-idUSKCN1J325H https://www.reuters.com/article/us-climatechange-carbon/scie...