I think logically you need the same order of magnitude to remove CO2 from the atmosphere as you gained form burning the fossil fuels. But I'm not sure where the practical limit is.
The only solution that makes remotely sense is using large areas of the ocean where nothing grows anyway and have a fleet of hundreds of ships that seed out algae that grows, absorbs sunlight and CO2 and then rains down on the ocean floor to sequester the carbon. Otherwise we don't have the land, energy and resources and money to do any of this.