Geoengineering Downwelling Ocean Currents: A Cost Assessment

Abstract

Downwelling ocean currents carry carbon into the deep ocean (the solubility pump), and play a role in controlling the level of atmospheric carbon. The formation of North Atlantic Deep Water (NADW) also releases heat to the atmosphere, which is a contributor to a mild climate in Europe. One possible response to the increase in anthropogenic carbon in the atmosphere and to the possible weakening of the NADW is modification of downwelling ocean currents, by an increase in carbon concentration or volume. This study assesses the costs of seven possible methods of modifying downwelling currents, including using existing industrial techniques for exchange of heat between water and air. Increasing carbon concentration in downwelling currents is not practical due to the high degree of saturation of high latitude surface water. Two of the methods for increasing the volume of downwelling currents were found to be impractical, and four were too expensive to warrant further consideration. Formation of thicker sea ice by pumping ocean water onto the surface of ice sheets is the least expensive of the methods identified for enhancing downwelling ocean currents. Modifying downwelling ocean currents is highly unlikely to ever be a competitive method of sequestering carbon in the deep ocean, but may find future application for climate modification.

The radiative forcing potential of different climate geoengineering options

“…A range of methods aimed at increasing the North Atlantic Deep Water (NADW) production by 1 Sverdrup (Sv, 10 6 m 3 s −1 ), from its current flow rate of 13-20 Sv, have been considered (Zhou and Flynn, 2005). This could be achieved by cooling surface waters by 1 • C, by having large floating pumps that form and thicken sea ice.…”

“…This could be achieved by cooling surface waters by 1 • C, by having large floating pumps that form and thicken sea ice. The increase in downwelling current has been estimated to lead to a net annual incremental flux of 0.0095 PgC yr −1 (Zhou and Flynn, 2005). Assuming activity starts in 2020, and that storage is permanent, and allowing for atmospheric adjustment, in 2050 a total of 0.18 PgC (0.08 ppm) would be removed from the atmosphere, giving a maximum RF(2050)≈−0.00095 W m −2 .…”

“…Suggestions for enhancing the solubility pump include increasing deep water production (i.e. downwelling in key regions) (Zhou and Flynn, 2005). Alternatively, increasing the alkalinity of the oceans through the addition of carbonate minerals should allow more CO 2 to be absorbed (Kheshgi, 1995;Harvey, 2008).…”

Arctic Climate Tipping Points

“…The other avoidance strategy is the more controversial deliberate geoengineering of Arctic climate (Zhou and Flynn 2005;Caldeira and Wood 2008). Some commentators have suggested replacing the declining blanket of cooling sulphate aerosols in the Arctic troposphere with a deliberate injection of sulphate (or other cooling aerosol) into the Arctic stratosphere (Caldeira and Wood 2008).…”

Ocean fertilization: a potential means of geoengineering?

“…The solubility pump has increased since pre-industrial times as a result of increasing atmospheric CO 2 concentration and this historically recent ocean sink for anthropogenic CO 2 is currently estimated to be approximately 2 GtC yr K1 (IPCC 2007). The ways in which direct action can be taken to enhance the ocean solubility pump still further have been considered with the final conclusion that they are 'highly unlikely to ever be a competitive method of sequestering carbon in the deep ocean' (Zhou & Flynn 2005) because the CO 2 cost of implementing them will outweigh the benefits.…”