浅析新生代气候变化与大气温室气体浓度的关系

On the Cenozoic climate changes and greenhouse gases

根据国内外相关研究结果,对新生代气候变化与温室气体(特别是CO2)浓度在不同时间尺度上的可能关系进行初步归纳和探讨。在构造、轨道和千年时间尺度上,气候变化和温室气体浓度均有显著的相关性,表明温室气体无疑是影响地球气候系统的重要因素。同时,两者亦具有显著的"非耦合"特征,包括新近纪构造尺度上CO2相对稳定水平下的全球变冷和冰量扩张、轨道和千年尺度上CO2浓度变化滞后于气候变化、两半球气候的不对称演化等;两者变化的幅度、趋势和变率也常有不同。这些特征中的多数并不能用地球轨道参数的变化来直接解释,表明除太阳辐射和温室气体外,气候系统内部的其他一些因素或过程有时对过去的气候变化起到了决定性的作用。气候变化与温室气体浓度之间可能存在一种自调节功能,构成一个自调节系统而相互调控,而目前我们对这类过程与机理所知尚少。CO2、CH4等作为温室气体,在上述不同时间尺度的气候变化过程中,无疑对气温具正反馈效应。地质尺度上气候变化与温室气体浓度的关系与机理有助于理解当前全球增温的机制,但把过去与现在类比的同时,也要考虑其他边界条件的不同。加强气候模拟与记录对比的研究,对理解上述问题有望发挥重要作用。

Based on the available data,earlier studies and our own recent results,in this paper we discuss the potential links between the Cenozoic climate changes and the atmospheric concentrations of greenhouse gases at the tectonic,orbital and millennial timescales with special emphasis given to CO2.The comparisons show a generally coupling between them,indicating that the greenhouse gases are among the most prominent driving forces of the climate system.However,a significant amount of decoupled aspects is also clear.These include the long-term global cooling and ice volume increase during the Neogene under relatively stable CO2 concentrations,the strong asymmetry of hemispheric climates at the glacial-interglacial scale during the mid-Pleistocene,and the seesaw pattern between the Southern and Northern Hemispheres at millennial scales.Also,most of the studies showed that the change in the CO2 concentration at the orbital and millennial scales lagged the change of the global temperature,which suggested that the changes in the CO2 concentration at these timescales were likely induced by climate changes,but may have a significant feedback of CO2 to climate conditions in modulating the amplitudes of climate changes.The climate-CO2 relationships during the Cenozoic are helpful for understanding the mechanisms of the ongoing global warming,but the differences in the boundary conditions between the geological past and the present-day must be taken into consideration.Climate and greenhouse gases may be,to some extent,a self-modulated system while little is known about the relevant processes.Data-model comparisons would be of great value towards understanding these links.