Producing CO2 is an exothermic process, and therefore easy - just set stuff on fire and it keeps going on its own. Removing CO2 is an endothermic ("energy-inten

Producing CO2 is an exothermic process, and therefore easy - just set stuff on fire and it keeps going on its own. Removing CO2 is an endothermic ("energy-intensive") process, and therefore hard; moreover, a lot of our energy-making just makes more CO2, thereby stumping any CO2 removal attempt. In other words, low CO2 is uphill from where we are, whereas high CO2 is downhill. And the slope is steep due to the laws of thermodynamics and chemistry.