CO2 tax is indeed the only way I think. Even if all ground transport and the grid is carbon free, we still have massive CO2 output in industry, agriculture, housing and airline industry - there's no way to fix that if the massive external effect CO2 has, is not paid by the consumer. It should create a CO2 market that puts a price on capturing it, with whatever is the best (cheapest) method at the time. We already have that with the certificates, but should be careful with those as they seem to be not the most cost efficient way of getting to negative carbon - a lot of money is afaik. flowing to developing nations that have below-average carbon emissions (at least as officially captured), without actually having to plant any trees.