Transient Response of the Hadley Centre Coupled Ocean-Atmosphere Model to Increasing Carbon Dioxide

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doi: 10.1175/1520-0442(1995)008<0057:TROTHC>2.0.CO;2 Journal of Climate: Vol. 8, No. 1, pp. 57–80. Transient Response of the Hadley Centre Coupled Ocean-Atmosphere Model to Increasing Carbon Dioxide. Part II: Spatial and Temporal Structure of Response J.M. Murphy and J.F.B. Mitchell Hadley Centre for Climate Prediction and Research, Meteorological Office, Bracknell, Berkshire, United Kingdom (Manuscript received November 11, 1993, in final form March 1, 1994)     ABSTRACT     A high-resolution (2.75° lat × ° 3.75° long) coupled ocean-atmosphere model has been used to simulate the transient response of climate to a gradual increase in atmospheric carbon dioxide concentrations. Although the radiative forcing increases linearly, there is a delay of about 30 yr before the ocean warms appreciably. This “cold start” is, at least partly, an artifact of the experimental design. At the time of doubling (after 70 yr), the patterns of change are similar to those found in comparable studies of the equilibrium response, except in the high latitudes of the Southern Ocean and the North Atlantic, where the warming is considerably reduced. The mechanisms leading to this reduction are discussed. After two to three decades, the pattern of warming is well established. The warming over land is substantially larger than that over the sea, with a consequent lowering of surface pressure over the northern continents in summer. The patterns of changes in precipitation and soil moisture take longer to establish themselves, although locally there are consistent changes after the third decade.