How accurately can the climate sensitivity to CO2\documentclass[12pt] end be estimated from historical climate change?
How accurately can the climate sensitivity to CO2\documentclass[12pt] end be estimated from historical climate change?
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DOI：
10.1007/s00382-019-04991-y
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发表时间：
2020-01-01
期刊：
影响因子：
4.6
通讯作者：
Webb, M. J.
中科院分区：
文献类型：
--
作者：
Gregory, J. M.;Andrews, T.;Webb, M. J.
平衡气候对CO2\documentclass [12 pt]倍增的敏感性（ECS，单位K）是未来人为气候变化预测中不确定性的一个很大来源。根据非平衡状态或响应于2xCO 2以外的辐射强迫对ECS的估计称为“有效气候敏感性”（EffCS，单位为K）。采用“完美模式”方法，使用耦合大气-海洋环流模式（AOGCM）实验，我们评估了从“历史”时期（大约1860年以来）的气候变化中估算CO2\documentclass [12 pt] EffCS的准确性。我们发现：（1）由于统计原因，非强迫变异性使得历史效应控制系统的估计既不确定又有偏差;如果将能量平衡应用于整个历史时期，则高估了约10%，30年时期高估了20%，而年际变率的因素更大，（2）历史辐射强迫的系统不确定性转化为+/-30至45%的不确定性\documentclass [12 pt]（标准差），（3）对强迫因子相对重要性变化的响应，主要是CO2\documentclass [12 pt]和火山气溶胶，导致历史EffCS在几十年的时间尺度上以两倍的因子变化。近几十年来，它在AOGCM历史实验中达到了最大值（类似于理想化实验中3.6 K的多模型平均CO2\documentclass[12 pt] EffCS），但其在真实的世界中的最小值（1985-2011年的观测估计值为1.6 K，类似于火山强迫的多模式平均值）。真实世界的变化意味着历史EffCS低估了CO2\documentclass [12 pt]在考虑整个历史时期时，EffCS降低30%。近几十年的差异意味着，无论是非强迫变率或对火山强迫的反应，导致一个强得多的区域模式的海表温度变化在真实的世界比AOGCM。我们推测，这可以解释为模拟耦合大气-海洋反馈，加强模式（类似的年代际太平洋涛动在某些方面），导致低EffCS的不足。我们得出结论，CO2\documentclass [12 pt] EffCS的能量平衡估计在未受火山强迫影响的时期最为准确。20世纪20年代至50年代，大气GCM提供了观测到的海面温度，这是这样一个时期，给出了约2.0-4.5 K的范围，与理想化的CO2\documentclass[12 pt]AOGCM实验一致;一致性是在此范围内作为CO2\documentclass[12 pt] EffCS估计值的置信度的原因。除非发生另一次火山爆发，否则本世纪的前30年可能会对这一数量作出更准确的能量平衡历史估计。
The equilibrium climate sensitivity (ECS, in K) to CO2\documentclass[12pt] doubling is a large source of uncertainty in projections of future anthropogenic climate change. Estimates of ECS made from non-equilibrium states or in response to radiative forcings other than 2xCO2\documentclass[12pt]are called "effective climate sensitivity" (EffCS, in K). Taking a "perfect-model" approach, using coupled atmosphere-ocean general circulation model (AOGCM) experiments, we evaluate the accuracy with which CO2\documentclass[12pt] EffCS can be estimated from climate change in the "historical" period (since about 1860). We find that (1) for statistical reasons, unforced variability makes the estimate of historical EffCS both uncertain and biased; it is overestimated by about 10% if the energy balance is applied to the entire historical period, 20% for 30-year periods, and larger factors for interannual variability, (2) systematic uncertainty in historical radiative forcing translates into an uncertainty of +/- 30to45%\documentclass[12pt](standard deviation) in historical EffCS, (3) the response to the changing relative importance of the forcing agents, principally CO2\documentclass[12pt] and volcanic aerosol, causes historical EffCS to vary over multidecadal timescales by a factor of two. In recent decades it reached its maximum in the AOGCM historical experiment (similar to the multimodel-mean CO2\documentclass[12pt] EffCS of 3.6 K from idealised experiments), but its minimum in the real world (1.6 K for an observational estimate for 1985-2011, similar to the multimodel-mean value for volcanic forcing).The real-world variations mean that historical EffCS underestimates CO2\documentclass[12pt] EffCS by 30% when considering the entire historical period. The difference for recent decades implies that either unforced variability or the response to volcanic forcing causes a much stronger regional pattern of sea surface temperature change in the real world than in AOGCMs. We speculate that this could be explained by a deficiency in simulated coupled atmosphere-ocean feedbacks which reinforce the pattern (resembling the Interdecadal Pacific Oscillation in some respects) that causes the low EffCS. We conclude that energy-balance estimates of CO2\documentclass[12pt] EffCS are most accurate from periods unaffected by volcanic forcing. Atmosphere GCMs provided with observed sea surface temperature for the 1920s to the 1950s, which was such a period, give a range of about 2.0-4.5 K, agreeing with idealised CO2\documentclass[12pt]AOGCM experiments; the consistency is a reason for confidence in this range as an estimate of CO2\documentclass[12pt] EffCS. Unless another explosive volcanic eruption occurs, the first 30 years of the present century may give a more accurate energy-balance historical estimate of this quantity.