末次冰盛期气候反馈特征研究

末次冰盛期(Last Glacial Maximum,简称LGM)被认为是较适合用来估算气候系统响应对辐射强迫变化的古气候区间之一.理解LGM时期气候反馈过程有助于进一步限定气候敏感度的范围.本研究利用辐射核方法和参加第三次古气候模式比较计划(Paleoclimate Modelling Intercomparison Project Phase Ⅲ,简称PMIP3)的8个耦合模式资料,对比研究了LGM时期与abrupt4xCO2(4CO2)情景下的气候反馈特征.结果表明:全球平均而言,不同情景下温度反馈、水汽反馈和反照率反馈的强度存在显著差异,然而这一关系并不存在于云反馈过程中,这可能与情景间/模式间云反馈的不确定性相联系;在不同情景下,不同反馈过程强度也存在明显空间差异.温度反馈过程的差异主要来源于LGM时期大陆冰盖强迫引起的温度变化的高度空间不均一性和海陆分布改变引起的热带对流活动的变化;水汽反馈变化可能与海陆分布变化引起的沃克环流变化以及全球降温相联系;大陆冰盖和海冰存在是导致LGM时期地表反照率反馈增加的主要原因;而云反馈的差异可能与低云云量和模式间不确定性有关.LGM时期单独强迫数值试验将有助于进一步厘清不同气候状态下气候反馈过程差异的原因.

Climate feedbacks at the Last Glacial Maximum

Assessing the impact of future global warming is impeded by the large range of Equilibrium Climate Sensitivity (ECS) to atmospheric CO2 doubling.Previous studies suggested the Last Glacial Maximum (LGM) is an ideal paleoclimate period to constrain the ECS since the abundant proxy data and coupled model simulations.However, the ECS inferred from LGM proxy data is still elusive since the climate feedback processes have not been well understood.In this study, the similarities and differences in the climate feedbacks, include temperature, water vapor, albedo and cloud feedback, for LGM and abrupt4xCO2 scenarios are investigated using the radiative kernel method and the Paleoclimate Modelling Intercomparison Project Phase Ⅲ(PMIP3) coupled model simulations.The results suggest that, in the global mean sense, the temperature, water vaper and albedo feedbacks have significant difference between LGM and abrupt4xCO2 scenarios, while the cloud feedback process is undistinguishable due to its uncertainties between scenarios and/or coupled models.The spatial distributions of feedback strengths are different in all feedback processes between scenarios.The discrepancy of temperature feedback between LGM and abrupt4xCO2 scenarios are due to highly inhomogeneous of surface temperature response due to the presence of continental ice sheets and tropical convection change because of the exposure of continental shelf.The difference in water vapor feedbacks over the equatorial eastern Pacific could be induced by the exposure of continental shelf and its induced Walker circulation change.The change of albedo feedback is consistent with the change of continental ice sheets/sea ice cover.The model uncertainty in cloud feedback strength and the change of low cloud between LGM and abrupt4xCO2 scenario could affect the total cloud feedback strength.Individual LGM forcing sensitive experiments are necessary for isolating the effect of each boundary forcing on the climate feedbacks.