Opinion: The importance of historical and paleoclimate aerosol radiative effects
Opinion: The importance of historical and paleoclimate aerosol radiative effects
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DOI：
10.5194/acp-24-533-2024
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发表时间：
2024-01
影响因子：
6.3
通讯作者：
N. Mahowald;Longlei Li;S. Albani;D. Hamilton;J. Kok
中科院分区：
文献类型：
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作者：
N. Mahowald;Longlei Li;S. Albani;D. Hamilton;J. Kok
抽象的。估算过去气溶胶辐射效应及其不确定性是气候科学中的一个重要课题。气溶胶辐射效应的传播，使对当前和未来气候如何随温室气体排放变化而演变的估计产生很大的不确定性。更深入地了解气溶胶如何影响过去气候下的大气能量收支，部分是由于缺乏相关的古观测，部分是因为对这个问题的关注较少。由于缺乏资料，我们在此不寻求确定气溶胶变化引起的辐射强迫的变化，而是估计这些变化的不确定性。在这里，我们认为，目前的排放不确定性（90%置信区间范围为2.8 W m−2）的不确定性是一样大的模型传播的不确定性（2.8 W m−2）在计算工业化前到今天的气溶胶辐射效应。在大多数古气候时期，没有对野火和沙尘气溶胶等重要气溶胶的辐射强迫的估计。然而，对古气候代用指标的定性分析表明，过去不同气候之间的气溶胶变化与工业化前和现在之间的气溶胶变化幅度相似;此外，工业化前气溶胶和火灾的变化增加了不确定性。从有限的文献中，我们粗略地估计了末次盛冰期相对于工业化前的古气候气溶胶不确定性为4.8 W m−2，我们估计自然地球系统中气溶胶反馈在古气候（末次盛冰期至工业化前）中的不确定性约为3.2 W m−2 K−1。为了更准确地评估历史气溶胶辐射效应的不确定性，我们提出了一个新的模型相互比较项目，其中包括在历史时期内在一系列最先进的气候模型中测试的多个合理的排放情景。然后将这些排放情景与现有的独立气溶胶观测进行比较，以限制最有可能的排放情景。此外，今后的努力应致力于表征和限制古气溶胶强迫和不确定性。为了确保对未来气候变化预测中的不确定性进行准确的量化，需要在文献中仔细传播气溶胶的不确定性。
Abstract. Estimating past aerosol radiative effects and their uncertainties is an important topic in climate science. Aerosol radiative effects propagate into large uncertainties in estimates of how present and future climate evolves with changing greenhouse gas emissions. A deeper understanding of how aerosols affected the atmospheric energy budget under past climates is hindered in part by a lack of relevant paleo-observations and in part because less attention has been paid to the problem. Because of the lack of information we do not seek here to determine the change in the radiative forcing due to aerosol changes but rather to estimate the uncertainties in those changes. Here we argue that current uncertainties from emission uncertainties (90 % confidence interval range spanning 2.8 W m−2) are just as large as model spread uncertainties (2.8 W m−2) in calculating preindustrial to present-day aerosol radiative effects. There are no estimates of radiative forcing for important aerosols such as wildfire and dust aerosols in most paleoclimate time periods. However, qualitative analysis of paleoclimate proxies suggests that changes in aerosols between different past climates are similar in magnitude to changes in aerosols between the preindustrial and present day; plus, there is the added uncertainty from the variability in aerosols and fires in the preindustrial. From the limited literature we crudely estimate a paleoclimate aerosol uncertainty for the Last Glacial Maximum relative to preindustrial of 4.8 W m−2, and we estimate the uncertainty in the aerosol feedback in the natural Earth system over the paleoclimate (Last Glacial Maximum to preindustrial) to be about 3.2 W m−2 K−1. In order to more accurately assess the uncertainty in historical aerosol radiative effects, we propose a new model intercomparison project, which would include multiple plausible emission scenarios tested across a range of state-of-the-art climate models over the historical period. These emission scenarios would then be compared to the available independent aerosol observations to constrain which are most probable. In addition, future efforts should work to characterize and constrain paleo-aerosol forcings and uncertainties. Careful propagation of aerosol uncertainties in the literature is required to ensure an accurate quantification of uncertainties in projections of future climate changes.