[论文解读] Global to local impacts on atmospheric CO2 caused by COVID-19 lockdown

Ning Zeng, Pengfei Han+11 more|arXiv (Cornell University)|Oct 25, 2020

Atmospheric and Environmental Gas Dynamics参考文献 16被引用 6

一句话总结

本研究利用高分辨率大气输送模型和观测数据，量化了2020年COVID-19封锁措施对大气CO2的影响，发现2020年2月至4月期间全球柱状CO2浓度下降了可检测到的0.13 ppm——主要由化石燃料排放减少（54%）驱动，生物圈和气象变异性各贡献23%。尽管信号较小，但这是过去十年中最大的年度内异常，可通过卫星和地面监测系统观测到。

ABSTRACT

The world-wide lockdown in response to the COVID-19 pandemic in year 2020 led to economic slowdown and large reduction of fossil fuel CO2 emissions, but it is unclear how much it would reduce atmospheric CO2 concentration, and whether it can be observed. We estimated that a 7.9% reduction in emissions for 4 months would result in a 0.25 ppm decrease in the Northern Hemisphere CO2, an increment that is within the capability of current CO2 analyzers, but is a few times smaller than natural CO2 variabilities caused by weather and the biosphere such as El Nino. We used a state-of-the-art atmospheric transport model to simulate CO2, driven by a new daily fossil fuel emissions dataset and hourly biospheric fluxes from a carbon cycle model forced with observed climate variability. Our results show a 0.13 ppm decrease in atmospheric column CO2 anomaly averaged over 50S-50N for the period February-April 2020 relative to a 10-year climatology. A similar decrease was observed by the carbon satellite GOSAT3. Using model sensitivity experiments, we further found that COVID, the biosphere and weather contributed 54%, 23%, and 23% respectively. This seemingly small change stands out as the largest sub-annual anomaly in the last 10 years. Measurements from global ground stations were analyzed. At city scale, on-road CO2 enhancement measured in Beijing shows reduction of 20-30 ppm, consistent with drastically reduced traffic during the lockdown. The ability of our current carbon monitoring systems in detecting the small and short-lasting COVID signal on the background of fossil fuel CO2 accumulated over the last two centuries is encouraging. The COVID-19 pandemic is an unintended experiment whose impact suggests that to keep atmospheric CO2 at a climate-safe level will require sustained effort of similar magnitude and improved accuracy and expanded spatiotemporal coverage of our monitoring systems.

研究动机与目标

• 量化2020年COVID-19封锁措施对全球和区域大气CO2的响应。
• 解析化石燃料排放、生物圈通量和气象变异性对观测到的CO2变化的贡献。
• 评估当前卫星和地面监测系统检测封锁引起的CO2信号的能力。
• 评估观测到的CO2异常是否显著高于自然变异性。
• 通过评估当前碳观测系统的灵敏度和能力，为未来气候监测提供建议。

提出的方法

• 采用先进的大气输送模型，利用新的每日化石燃料排放数据集模拟CO2分布。
• 结合由观测气候变异性驱动的碳循环模型提供的每小时生物圈通量。
• 使用2010–2019年的10年气候基准计算2020年2月至4月的CO2异常值。
• 开展模型敏感性实验，以分离化石燃料排放、生物圈和天气变异性各自的贡献。
• 通过独立的GOSAT卫星观测和北京的地面CO2测量数据验证结果。
• 分析北京道路CO2浓度的增强值，以评估封锁期间局部尺度的排放减少情况。

实验结果

研究问题

• RQ1 2020年COVID-19封锁措施在多大程度上导致了全球和区域大气CO2浓度的降低？
• RQ2 化石燃料排放、生物圈通量和气象变异性如何共同导致观测到的CO2异常？
• RQ3 当前监测系统能否在自然变异性之上检测到封锁引起的CO2信号？
• RQ4 北半球和全球范围内的CO2异常在多大程度上具有显著的幅度和空间分布特征？
• RQ5 地面观测与卫星观测在检测因排放减少引起的短期CO2信号方面表现如何？

主要发现

• 四个月内化石燃料CO2排放量减少了7.9%，导致2020年2月至4月期间全球柱状CO2浓度下降0.13 ppm。
• 观测到的CO2异常主要由化石燃料排放减少（54%）驱动，生物圈和气象变异性各贡献23%。
• 0.13 ppm的下降是过去10年中最大的年度内CO2异常，可被当前CO2分析仪检测到。
• GOSAT卫星观测证实了模型中CO2的减少，验证了模型准确捕捉该信号的能力。
• 在北京，封锁期间道路CO2浓度增强值下降了20–30 ppm，与交通减少和局部排放减少一致。
• 尽管受过去两个世纪化石燃料使用导致的背景积累影响，当前碳监测系统仍具备检测短期、小尺度CO2信号的能力。