Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes
Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes
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DOI：
10.5194/acp-20-15461-2020
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发表时间：
2019-01
影响因子：
6.3
通讯作者：
Abdul Malik;P. Nowack;J. Haigh;Long Cao;Luqman Atique;Y. Plancherel
中科院分区：
文献类型：
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作者：
Abdul Malik;P. Nowack;J. Haigh;Long Cao;Luqman Atique;Y. Plancherel
抽象的。许多模拟研究表明，厄尔尼诺-南方涛动与热带太平洋背景气候相互作用，将随着大气温室气体浓度的上升而发生变化。太阳地球工程（减少来自外层空间的太阳通量）被提议作为抵消人为气候变化的一种手段。然而，太阳地球工程对地球气候各个方面的有效性尚不确定。要获得厄尔尼诺/南方涛动的可靠结果特别具有挑战性，因为现有的地球工程模拟太短（通常为50年），无法检测高度可变的热带太平洋背景气候的统计学显著变化。在这里，我们提出的结果，从1000年之久的太阳地球工程模拟，G1，进行了耦合大气-海洋环流模式HadCM 3L。与以前的研究一致，减少太阳辐照度（4%）以抵消模型中的全球平均表面变暖，超过了4 × CO2情景中热带太平洋的变暖。由于短波（太阳）和长波（CO2）强迫的不同纬度分布，我们看到热带太平洋相对于工业化前条件下的过冷0.3 ° C和平均降雨量减少0.23 mm d−1（5%）。热带太平洋的热带辐合带（ITCZ）在4 × CO2条件下向南移动了7.5 ° C，恢复到工业化前的位置。然而，热带太平洋平均气候的其他方面并没有有效地重置。相对于工业化前的情况，在G1中，时间平均纬向风应力、纬向海表温度（SST）梯度和纬向SST梯度在统计上都显著降低了约10%，太平洋步行者环流（PWC）持续减弱，导致有利于厄尔尼诺事件频率增加的条件。ENSO的总体振幅在G1增强了9%-10%，但冷暖事件之间的不对称性减少了65%：冷事件比暖事件增强得多。值得注意的是，极端厄尔尼诺和拉尼娜事件的频率增加了约。60%和30%，而厄尔尼诺事件的总数增加了10%左右。所有这些变化在95%或99%置信水平下具有统计学显著性。有些自相矛盾的是，虽然总体和极端事件的数量增加，但极端厄尔尼诺事件相对于工业化前的状态变得较弱，而极端拉尼娜事件则变得更强。也就是说，G1中这种极端的厄尔尼诺事件比前工业化条件下的强度要小，但也更频繁。相反，极端拉尼娜事件在G1变得更强，这与G1热带太平洋相对于工业化前条件的总体过冷相一致。
Abstract. Many modelling studies suggest that the El Niño–Southern Oscillation (ENSO), in interaction with the tropical Pacific background climate, will change with rising atmospheric greenhouse gas concentrations. Solar geoengineering (reducing the solar flux from outer space) has been proposed as a means to counteract anthropogenic climate change. However, the effectiveness of solar geoengineering concerning a variety of aspects of Earth's climate is uncertain. Robust results are particularly challenging to obtain for ENSO because existing geoengineering simulations are too short (typically ∼ 50 years) to detect statistically significant changes in the highly variable tropical Pacific background climate. We here present results from a 1000-year-long solar-geoengineering simulation, G1, carried out with the coupled atmosphere–ocean general circulation model HadCM3L. In agreement with previous studies, reducing the solar irradiance (4 %) to offset global mean surface warming in the model more than compensates the warming in the tropical Pacific that develops in the 4 × CO2 scenario. We see an overcooling of 0.3 ∘C and a 0.23 mm d−1 (5 %) reduction in mean rainfall over the tropical Pacific relative to preindustrial conditions in the G1 simulation, owing to the different latitudinal distributions of the shortwave (solar) and longwave (CO2) forcings. The location of the Intertropical Convergence Zone (ITCZ) in the tropical Pacific, which moved 7.5∘ southwards under 4 × CO2, is restored to its preindustrial position. However, other aspects of the tropical Pacific mean climate are not reset as effectively. Relative to preindustrial conditions, in G1 the time-averaged zonal wind stress, zonal sea surface temperature (SST) gradient, and meridional SST gradient are each statistically significantly reduced by around 10 %, and the Pacific Walker Circulation (PWC) is consistently weakened, resulting in conditions conducive to increased frequency of El Niño events. The overall amplitude of ENSO strengthens by 9 %–10 % in G1, but there is a 65 % reduction in the asymmetry between cold and warm events: cold events intensify more than warm events. Notably, the frequency of extreme El Niño and La Niña events increases by ca. 60 % and 30 %, respectively, while the total number of El Niño events increases by around 10 %. All of these changes are statistically significant at either 95 or 99 % confidence level. Somewhat paradoxically, while the number of total and extreme events increases, the extreme El Niño events become weaker relative to the preindustrial state, while the extreme La Niña events become even stronger. That is, such extreme El Niño events in G1 become less intense than under preindustrial conditions but also more frequent. In contrast, extreme La Niña events become stronger in G1, which is in agreement with the general overcooling of the tropical Pacific in G1 relative to preindustrial conditions.