That particular plot point is about denying all solar energy to the machines. Needless to say it's a fictional movie and more serious calculations should motiva

That particular plot point is about denying all solar energy to the machines. Needless to say it's a fictional movie and more serious calculations should motivate our analyses. It's been estimated that current increases in CO2 have a radiative forcing effect of about 2 watts per square meter, compared to the total solar irradiance of 1361 W/m2. If CO2 levels doubled to 800 ppm then it's estimated this would have a radiative forcing effect of 6 W/m2. This scenario would require mitigation strategies like stratospheric aerosol injection to reduce solar irradiance by about 0.4%. In the context of plant growth this reduction in sunlight would be negligible given that photosynthesis is only 1 to 2% efficient. If anything we should see significantly accelerated plant growth by about 10 to 50% due to the CO2 fertilization effect at 800ppm. The alternatives consist of completely replacing all energy infrastructure, which will cost trillions of dollars and significantly reduce economic growth. We can already see the negative effects of these policies in Europe, such as Germany which irrationally shut down their nuclear reactors, pushed the deployment of solar, while ultimately relying on Russian natural gas. They now burn more coal than they did before, and risk deindustrializing due to high energy costs. This is an epic strategic blunder since China, India, and Africa will continue burning hydrocarbons irrespective of the West's economic self-sabotage. There's also no realistic way to extract the amount of CO2 that's been emitted into the atmosphere. Simple thermodynamics would have us expend far more energy than we cumulatively gained from burning hydrocarbons since the industrial revolution to extract such an extremely diffuse gas from the atmosphere.