Uncertainties in CMIP5 Climate Projections due to Carbon Cycle Feedbacks
Uncertainties in CMIP5 Climate Projections due to Carbon Cycle Feedbacks
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DOI：
10.1175/jcli-d-12-00579.1
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发表时间：
2014-01-01
影响因子：
4.9
通讯作者：
Knutti, Reto
中科院分区：
文献类型：
--
作者：
Friedlingstein, Pierre;Meinshausen, Malte;Knutti, Reto
在耦合模式相互比较项目第5阶段的背景下，大多数气候模拟使用规定的大气CO2浓度，因此不包括碳循环反馈的影响。然而，代表性的浓度路径8.5（RCP 8.5）的情况下，还运行了地球系统模型与规定的二氧化碳排放量。本文分析了11个地球系统模式（ESM）的气候预测，这些模式进行了排放驱动和浓度驱动的RCP8.5模拟。当受到RCP8.5 CO2排放的强制时，模型模拟了大气CO2的大范围扩散;模拟的2100年浓度范围在795至1145 ppm之间。11个ESM中有7个模拟了更大的CO2（平均为44 ppm，到2100年为985 +/- 97 ppm），因此当由CO2排放驱动时，辐射强迫比浓度驱动情景（941 ppm）更高（0.25 W m（-2））。然而，这些模型中的大多数已经高估了当前的CO2，当前的偏差与未来大气浓度偏离规定浓度的相关性相当好。CO2预测的不确定性主要归因于陆地碳循环响应的不确定性。由于模拟的CO2浓度高于浓度驱动的模拟，当ESM由CO2排放驱动时，温度预测通常较高。到2100年，全球表面温度变化（相对于现在）在排放驱动的模拟中增加了3.9度+/- 0.9摄氏度，而在浓度驱动的模拟中增加了3.7度+/- 0.7摄氏度。虽然两组模拟的下限是可比的，但由于碳循环反馈更强，排放驱动模拟中的最高气候预测显着变暖。
In the context of phase 5 of the Coupled Model Intercomparison Project, most climate simulations use prescribed atmospheric CO2 concentration and therefore do not interactively include the effect of carbon cycle feedbacks. However, the representative concentration pathway 8.5 (RCP8.5) scenario has additionally been run by earth system models with prescribed CO2 emissions. This paper analyzes the climate projections of 11 earth system models (ESMs) that performed both emission-driven and concentration-driven RCP8.5 simulations. When forced by RCP8.5 CO2 emissions, models simulate a large spread in atmospheric CO2; the simulated 2100 concentrations range between 795 and 1145 ppm. Seven out of the 11 ESMs simulate a larger CO2 (on average by 44 ppm, 985 +/- 97 ppm by 2100) and hence higher radiative forcing (by 0.25 W m(-2)) when driven by CO2 emissions than for the concentration-driven scenarios (941 ppm). However, most of these models already overestimate the present-day CO2, with the present-day biases reasonably well correlated with future atmospheric concentrations' departure from the prescribed concentration. The uncertainty in CO2 projections is mainly attributable to uncertainties in the response of the land carbon cycle. As a result of simulated higher CO2 concentrations than in the concentration-driven simulations, temperature projections are generally higher when ESMs are driven with CO2 emissions. Global surface temperature change by 2100 (relative to present day) increased by 3.9 degrees +/- 0.9 degrees C for the emission-driven simulations compared to 3.7 degrees +/- 0.7 degrees C in the concentration-driven simulations. Although the lower ends are comparable in both sets of simulations, the highest climate projections are significantly warmer in the emission-driven simulations because of stronger carbon cycle feedbacks.