A device and method for carbon dioxide capture using circumscribed hollow membranes is disclosed. The device includes a hollow membrane unit having an inner conduit composed of a vapor membrane, and an outer conduit having an inside surface circumscribing the inner conduit forming a lumen. The outer conduit includes a CO2 pump membrane. The device also includes a mechanical pump maintaining a pressure differential between the lumen and the atmosphere, providing a product stream of CO2-rich gas from the lumen. The vapor membrane is sufficiently hydrophobic and porous to contain liquid water while also allowing water vapor formed by evaporation to pass through into the lumen. As water vapor passes from the lumen to the atmosphere through the CO2 pump membrane, a carbon concentration gradient is formed and maintained across the CO2 pump membrane. The carbon concentration gradient actively pumps CO2 out of the atmosphere and into the lumen.