关键词: 温室效应, 缓变气候效应, 海洋模式

Abstract: Greenhouse gas-induced global climate change has been attracted much attention in recent years. Model studies suggest that the equilibrium warming for a CO₂ doubling is 1. 5 ℃-4.5℃ (climate sensitivity). However. because the huge thermal capacity of the ocean will delay and effectively reduce the climate response to the increase in the concentration of the greenhouse gases, at a given time, the realized global surface temperature will only reflect part of the equilibrium change for the corresponding instantaneous value of the radiative forcings induced by greenhouse-gases. In this study, we have developed a coupled EBM/BD model to study the greenhouse-gas induced transient and time-dependent change of global mean temperature. The model consists of three parts, i. e., the atmosphere, land and ocean. The atmosphere and the land are considered as boxes. The ocean is divided into a oceanic mixed layer, a thermocline layer and a bottom layer. The heat exchanges of atmosphere-land,atmosphere-oceanic mixed layer and land-oceanic mixed layer are described by using the energy balance model developed by Wigley and Schlesinger. The heat exchanges of oceanic mixed layer-thermocline layer, mixed layer-bottom layer and thermocline layer-bottom layer are described by using our BD model previously developed for study of the carbon circle. The validity of the model is investigated by comparing the simulated and observed vertical distributions of ocean water temperature. A doubling CO₂ experiment is performed to investigate the response of the ocean surface temperature to the increase in the concentration of the greenhouse gases. In the experiment,the radiative forcing due to doubling CO₂ is 4. 23w/m2. The results show that the thermal inertia of the ocean provides a time lag of about 1 1. 08- 101. 48 years, depending on the values of climate sensitivity. The model is also used to simulate the variation of the ground surface temperature in the past 100 years by using the radiative forcings derived from the concentrations of greenhouse gases given by Wigley. The results show that the ground surface temperature has risen about 0. 35-0. 64℃. corresponding to the climate sensitivity of 1. 54-4.5℃. Such results are consistent with the observed rise of about 0. 3℃-0. 6℃. The consistence between the simulated and observed rise of the ground surface temperature indicates that the increase in the concentrations of the greenhouse gases plays a main role in the rise of the ground surface temperature in the past 100 years. The CO₂ concentration of the next century has been simulated by using the BD model for several emission scenarios given by IPCC. If the humankind does not control the CO₂ emissions from now. the CO₂ concentration will reach a value of 743ppmv at the end of the next century. If the CO₂ emissions are reduced at a rate of 2% per year. the CO₂ concentration will slowly increase until 2050 and reach a peak value of 390ppmv. After 2050, the CO₂ concentration will decrease. If the CO₂ emissions are stopped from now, the CO₂ concentration will slowly decrease and reach a value of 320ppmv at the end of the next century. The variations of the ground surface temperature of the next century are estimated by using the coupled model. The results show that. if the humankind does not control the CO₂ emissions, the ground surface temperature at the end of the next century will rise about 1. 64℃-3. 08℃ for the climate sensitivity of 1. 5℃-4. 5℃. If the CO₂ emissions are reduced at a rate of 2% per year, the ground surface temperature will slowly rise in the beginning and middle decades of the next century. The ground surface temperature will not change in the late decades. If the CO₂ emissions can be stopped from now, The ground surface temperature will decrease slowly.

Key words: greenhouse effect, time-dependent climate change, ocean model