None of the geoengineering solutions address the other major issue with our fossil fuel usage, which is ocean acidification. Even if we could just lower the temperature, lots of the CO2 pumped into the air gets absorbed into the oceans, like in a bottle of soda, making it more acidic. When this happens, it makes it harder for all the life at the bottom of the food chain to form, causing a mass die off at the base. If things get bad enough It could lead to the collapse of the food chain and we would just starve to death.