Collaborative Research: Quantifying the sea-surface temperature pattern effect for Last Glacial Maximum and Pliocene constraints on climate sensitivity

对未来气候变化的预测在一定程度上是基于不同气候时代的地质记录所看到的变化。这些时期包括2.1万年前的最后一次冰川盛期(LGM)(大气中二氧化碳水平较低的较冷时期)和530万至260万年前的上新世(二氧化碳含量较高的较温暖时期)。这些周期可以用来估计气候对二氧化碳等温室气体变化的敏感性。这些敏感性估计有助于预测未来温室气体排放所应看到的全球变暖程度。然而，最近的研究表明，气候对温室气体的敏感性不仅取决于地表平均温度的变化，还取决于这种变化的地理模式。因此，使用地质古气候记录来估计未来变暖必须考虑到过去温度变化的空间模式与未来预期的不同之处。该项目将结合来自古气候数据和气候模型的信息来评估末次盛冰期和上新世期间地表温度变化的空间模式。然后，它将开发方法，在使用这些过去时期的数据来帮助估计未来全球变暖时，考虑温度模式的差异。地球的平衡气候敏感度(ECS)是与大气二氧化碳浓度(CO2)相对于工业化前大气翻一番而导致的表面平均温度的变化。ECS是由辐射反馈设置的，这些辐射反馈将地表变暖与离开地球大气层的辐射量的变化联系起来。最近的研究表明，全球辐射反馈取决于海表面温度(SST)的空间格局。根据过去气候变化的替代记录--例如上次冰川盛期(LGM)和上新世的气候变化--对ECS的估计传统上是基于全球平均能源预算限制，因此没有考虑到这些国家的SST模式可能与未来的模式有何不同。这项研究将使用最近开发的数据同化技术，结合来自气候模式和代理数据的信息，重建与现有代理数据动态一致的LGM和上新世的格网SST场。然后将这些海温场与二氧化碳强迫下的全球气候模型预测的海温场进行比较。然后将使用一套大气环流模式和将变暖模式与辐射反馈联系起来的格林函数来量化辐射反馈对LGM/上新世和二氧化碳强迫SST模式之间差异的敏感性。通过产生LGM和上新世地表温度模式的估计，并量化温度模式差异对辐射反馈的影响，这项研究将改善我们对来自过去气候状态的ECS的理解。这项工作将进一步促进研究人员参与旨在向高中生介绍气候科学的活动，通过华盛顿大学气候变化计划和乔治梅森大学有抱负的科学家暑期实习计划为高中教师举办的当前气候科学研讨会。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Predictions of future climate change are based in part on changes seen in geological records of times with different climates. Such times include the Last Glacial Maximum (LGM) 21 thousand years ago (a colder time with lower atmospheric carbon dioxide levels) and the Pliocene Epoch 5.3 to 2.6 million years ago (a warmer time with higher carbon dioxide). These periods can be used to estimate the sensitivity of climate to changes in greenhouse gases such as carbon dioxide. Those sensitivity estimates help predict the amount of global warming we should expect to see in response to future greenhouse gas emissions. However, recent work has shown that the climate’s sensitivity to greenhouse gases depends not only on the average surface temperature change but also on the geographic pattern of that change. Thus, use of geological paleoclimate records to estimate future warming must account for how the spatial pattern of temperature changes in the past differs from that expected in the future. This project will combine information from paleoclimate data and climate models to evaluate the spatial pattern of surface temperature changes during the LGM and Pliocene. It will then develop methods to account for temperature pattern differences when using data from these past periods to help estimate future global warming.Earth’s equilibrium climate sensitivity (ECS) is the change in average surface temperature associated with a doubling of the atmospheric carbon dioxide concentration (CO2) relative to the pre-industrial atmosphere. The ECS is set by the radiative feedbacks that link surface warming to changes in the amount of radiation leaving Earth’s atmosphere. Recent studies have shown that global radiative feedbacks depend on the spatial pattern of sea-surface temperature (SST). Estimates of ECS based on the proxy record of past climate changes – such as those during the Last Glacial Maximum (LGM) and Pliocene – have traditionally been based on global mean energy budget constraints and thus do not account for how SST patterns in those states may be different from those in the future. This research will use recently developed data assimilation techniques, combining information from climate models and proxies, to reconstruct gridded SST fields for the LGM and Pliocene that are dynamically consistent with available proxy data. These SST fields will then be compared against those projected by global climate models under CO2 forcing. The sensitivity of radiative feedbacks to differences between LGM / Pliocene and CO2-forced SST patterns will then be quantified using a suite of atmospheric general circulation models and Green’s functions that link warming patterns to radiative feedbacks. By producing estimates of LGM and Pliocene surface temperature patterns and quantifying the impact of temperature pattern differences on radiative feedbacks, this research will improve our understanding of ECS derived from those past climate states. This work will further facilitate researchers’ participation in activities aimed at introducing high school students to climate science, through Current Climate Science workshops for high school teachers facilitated by the University of Washington’s Program on Climate Change and through George Mason University’s Aspiring Scientists Summer Internship Program.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.