TY - JOUR
T1 - Response of the Atlantic thermohaline circulation to increased atmospheric CO2 in a coupled model
AU - Hu, Aixue
AU - Meehl, Gerald A.
AU - Washington, Warren M.
AU - Dai, Aiguo
PY - 2004/11/1
Y1 - 2004/11/1
N2 - Changes in the thermohaline circulation (THC due to increased C0 2 are important in future climate regimes. Using a coupled climate model, the Parallel Climate Model (PCM), regional responses of the THC in the North Atlantic to increased C02 and the underlying physical processes are studied here. The Atlantic THC shows a 20-yr cycle in the control run, qualitatively agreeing with other modeling results. Compared with the control run, the simulated maximum of the Atlantic THC weakens by about 5 Sv (1 Sv 106 M3 S-1) Or 14% in an ensemble of transient experiments with a 1% C02 increase per year at the time of C02 doubling. The weakening of the THC is accompanied by reduced poleward heat transport in the midlatitude North Atlantic. Analyses show that oceanic deep convective activity strengthens significantly in the Greenland-Iceland-Norway (GIN) Seas owing to a saltier (denser) upper ocean, but weakens in the abrador Sea due to a fresher (lighter) upper ocean and in the south of the Denmark Strait region (SDSR) because of surface warming. The saltiness of the GIN Seas are mainly caused by an increased salty North Atlantic inflow, and reduced sea ice volume fluxes from the Arctic into this region. The warmer SDSR is induced by a reduced heat loss to the atmosphere, and a reduced sea ice flux into this region, resulting in less heat being used to melt ice. Thus, sea ice-related salinity effect s appear to be more important in the GIN Seas, but sea ice-melt-related thermal effects seem to be more important in the SDSR region. On the other hand, the fresher Labrador Sea is mainly attributed to increased precipitation. These regional changes produce the overall weakening of the THC in the Labrador Sea and SDSR, and more vigorous ocean overturning in the GIN Seas. The northward heat transport south of 60°N is reduced with increased CO2 but increased north of 60°N due to the increased flow of North Atlantic water across this latitude.
AB - Changes in the thermohaline circulation (THC due to increased C0 2 are important in future climate regimes. Using a coupled climate model, the Parallel Climate Model (PCM), regional responses of the THC in the North Atlantic to increased C02 and the underlying physical processes are studied here. The Atlantic THC shows a 20-yr cycle in the control run, qualitatively agreeing with other modeling results. Compared with the control run, the simulated maximum of the Atlantic THC weakens by about 5 Sv (1 Sv 106 M3 S-1) Or 14% in an ensemble of transient experiments with a 1% C02 increase per year at the time of C02 doubling. The weakening of the THC is accompanied by reduced poleward heat transport in the midlatitude North Atlantic. Analyses show that oceanic deep convective activity strengthens significantly in the Greenland-Iceland-Norway (GIN) Seas owing to a saltier (denser) upper ocean, but weakens in the abrador Sea due to a fresher (lighter) upper ocean and in the south of the Denmark Strait region (SDSR) because of surface warming. The saltiness of the GIN Seas are mainly caused by an increased salty North Atlantic inflow, and reduced sea ice volume fluxes from the Arctic into this region. The warmer SDSR is induced by a reduced heat loss to the atmosphere, and a reduced sea ice flux into this region, resulting in less heat being used to melt ice. Thus, sea ice-related salinity effect s appear to be more important in the GIN Seas, but sea ice-melt-related thermal effects seem to be more important in the SDSR region. On the other hand, the fresher Labrador Sea is mainly attributed to increased precipitation. These regional changes produce the overall weakening of the THC in the Labrador Sea and SDSR, and more vigorous ocean overturning in the GIN Seas. The northward heat transport south of 60°N is reduced with increased CO2 but increased north of 60°N due to the increased flow of North Atlantic water across this latitude.
UR - https://www.scopus.com/pages/publications/2042475909
U2 - 10.1175/JCLI3208.1
DO - 10.1175/JCLI3208.1
M3 - Article
AN - SCOPUS:2042475909
SN - 0894-8755
VL - 17
SP - 4267
EP - 4279
JO - Journal of Climate
JF - Journal of Climate
IS - 21
ER -