Reassessing the relative role of anthropogenic aerosols and natural decadal variability in driving the mid-twentieth century global “cooling”: a focus on the latitudinal gradient of tropospheric temperature
Reassessing the relative role of anthropogenic aerosols and natural decadal variability in driving the mid-twentieth century global “cooling”: a focus on the latitudinal gradient of tropospheric temperature
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DOI：
10.1007/s00382-022-06235-y
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发表时间：
2022-03
期刊：
影响因子：
4.6
通讯作者：
C. Diao;Yangyang Xu
中科院分区：
文献类型：
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作者：
C. Diao;Yangyang Xu
全球平均地表温度在世纪中期略有降温，尽管温室气体浓度持续增加。北方半球中纬度地区的冷却最强，而南半球中纬度地区则经历了适度的变暖。这种明显的矛盾通常归因于源自太平洋和大西洋海洋与大气相互作用的内部数十年变化。考虑到这一时期北美和欧洲工业活动的迅速增加，人为气溶胶（AA）排放（作为外部强迫）对北方半球更强的冷却也有可能做出贡献。本文的目的是量化的AA和年代际变率的贡献，1948-1978年的冷却。我们利用多个再分析数据集和耦合模式相互比较项目第5阶段（CMIP 5）多模式集合分析了整个对流层60° S-60° N的纬向温度趋势不对称性，该模式与观测模式具有显著的相似性。我们发现，AA增加和北大西洋变率指数（NAVI）过渡到其负相的纬度不对称的冷却的主要贡献者。在地面水平，基于水平模式相关方法，AA和NAVI具有相似的贡献分数（20 vs. 16%），但AA的贡献分数在500 hPa（55 vs. 8%）要大得多。基于垂直格局相关性和纬度梯度的归因结果一致。自然强迫（NAT）也有助于在20 ℃中期的冷却不对称性，但与AA和NAVI相比，其影响要小得多。因此，我们认为，以前的研究，主要集中在地面变量可能低估了AA在世纪中期的气候变化的作用。研究表明，在未来的气候归因分析中，应密切关注三维热力结构和大气环流变化。
The global mean surface temperature cooled slightly in the mid-twentieth century despite a continuous increase in greenhouse gas concentrations. The cooling was strongest in the Northern Hemisphere mid-latitudes, while the Southern Hemisphere mid-latitudes experienced moderate warming. This apparent contradiction is often attributed to internal multi-decadal variability originating from Pacific and Atlantic ocean-atmosphere interactions. Given the rapid increase of industrial activities in North America and Europe during that period, it is also plausible that anthropogenic aerosol (AA) emissions (as an external forcing) contributed to the stronger Northern Hemisphere cooling. This paper aims to quantify the contributions of AA and decadal variability to the 1948–1978 cooling. We analyzed the latitudinal temperature trend asymmetry in 60° S–60° N throughout the troposphere, using multiple reanalysis datasets and the Coupled Model Intercomparison Project phase 5 (CMIP5) multi-model ensemble that bears significant similarity with the observed patterns. We show that both AA increase and the North Atlantic Variability Index (NAVI) transition into its negative phase are the major contributors to the latitudinal asymmetry of cooling. At the surface level, based on the horizontal pattern correlation method, AA and NAVI have similar contribution fractions (20 vs. 16%), but the contribution fraction of AA is much larger at 500 hPa (55 vs. 8%). Attributions based on vertical pattern correlation and latitudinal gradient show consistent results. Natural forcings (NAT) also contribute to the cooling asymmetry during mid-20C, but with a much smaller impact compared to AA and NAVI. Therefore, we argue that previous studies that mostly focused on surface variables may have underestimated the role of AA in the mid-twentieth-century climate change. The study suggests that the three-dimensional thermal structure and atmospheric circulation change should be closely examined in future climate attribution analysis.