Oil and gas can be thought of as a giant battery. In both batteries and hydrocarbons, energy is held by chemical bonds. We can either break the bonds (burn it) to get energy out, or reform them by putting sufficient energy back in under the right conditions (usually high pressure).

Thus, we're discharging earth's hydrocarbon battery right now, but if we eventually have surplus energy, perhaps via sufficient solar, or nuclear, we could relatively easily pull carbon out of the air and sequester that carbon, either back into hydrocarbons or into some other carbon-based molecules.