给定海表温度模拟的地球反馈的统计噪声与强迫极限估计
Statistical Noise and Missing Forcing Limit Estimates of Earth's Feedback from Prescribed Sea-Surface Temperature Simulations
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中文总结 AI 辅助
该研究通过受控实验验证给定海表温度模拟估计地球反馈参数的两个假设，发现该方法因缺少大气强迫和统计噪声无法捕捉耦合反馈演变，难以推断观测期内地球参数的时间变化。
中文摘要 AI 辅助
地球反馈参数用于衡量地球系统对强迫的响应，且与气候敏感性成反比。海表温度（SST）模态可调节反馈参数的数值，观测与模拟的海表温度之间的差异引发了一个问题：观测到的海表温度演变如何影响全球反馈。估计该效应的标准方法是将观测到的海表温度施加于大气模式，并固定前工业时代的大气强迫，该方法做出两个假设：其一，观测到的海表温度已涵盖强迫的所有相关效应，因此无需施加随时间变化的强迫；其二，反馈参数的时间变化由演变的海表温度模态驱动，可通过滑动窗口回归进行估计。我们通过开展受控实验验证这些假设，将全耦合历史模拟中的海表温度施加于大气模式。结果发现，给定海表温度实验无法捕捉耦合反馈的演变，这可由两个效应解释：一是缺少大气强迫的施加，二是滑动窗口回归计算产生的统计噪声。在4000年的前工业时代控制模拟中，我们未发现演变的海表温度模态与反馈时间序列变化之间存在任何显著关系的证据，在短于约100年的时间尺度上检测到的反馈参数的任何趋势都与统计噪声无法区分，使其归因于演变的海表温度模态极为困难。我们的结果表明，给定海表温度模拟在推断观测期内地球参数的时间变化方面潜力有限。
英文摘要
Earth's feedback parameter measures how the Earth system responds to forcing and is inversely proportional to climate sensitivity. Sea-surface temperature (SST) patterns can modulate the value of the feedback parameter. Differences between observed and simulated SSTs have raised the question how the observed SSTs evolution impacts the global feedback. The standard method for estimating this effect uses observed SSTs prescribed to an atmospheric model with fixed pre-industrial atmospheric forcing. This method makes two assumptions: first, that the observed SSTs capture all relevant effects from the forcing, so that prescribing a time-varying forcing is unnecessary; second, that the temporal variations in the feedback parameter are driven by the evolving SST pattern and can be estimated via moving-window regressions. We test these assumptions by running controlled experiments in which SSTs from fully-coupled historical simulations are prescribed to an atmospheric model. We find that the prescribed-SST experiments fail to capture the coupled feedback evolution. This is explained by two effects: First, the absence of prescribed atmospheric forcing, and second, statistical noise arising from the computation of moving-window regressions. We find no evidence of any significant relationship between evolving SST patterns and changes in the feedback time series in a 4000-year pre-industrial control simulation. Any trends in the feedback parameter detected on timescales shorter than ~100 years are indistinguishable from statistical noise, making their attribution to the evolving SST pattern extremely difficult. Our results imply that prescribed SST simulations offer limited potential for inferring temporal changes in Earth's parameter over the observational period.
