State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, China.
Institute of Epidemiology, Helmholtz Zentrum München, Neuherberg, Germany.
PLoS Med. 2018 Jul 3;15(7):e1002598. doi: 10.1371/journal.pmed.1002598. eCollection 2018 Jul.
Climate change is likely to further worsen ozone pollution in already heavily polluted areas, leading to increased ozone-related health burdens. However, little evidence exists in China, the world's largest greenhouse gas emitter and most populated country. As China is embracing an aging population with changing population size and falling age-standardized mortality rates, the potential impact of population change on ozone-related health burdens is unclear. Moreover, little is known about the seasonal variation of ozone-related health burdens under climate change. We aimed to assess near-term (mid-21st century) future annual and seasonal excess mortality from short-term exposure to ambient ozone in 104 Chinese cities under 2 climate and emission change scenarios and 6 population change scenarios.
We collected historical ambient ozone observations, population change projections, and baseline mortality rates in 104 cities across China during April 27, 2013, to October 31, 2015 (2013-2015), which included approximately 13% of the total population of mainland China. Using historical ozone monitoring data, we performed bias correction and spatially downscaled future ozone projections at a coarse spatial resolution (2.0° × 2.5°) for the period April 27, 2053, to October 31, 2055 (2053-2055), from a global chemistry-climate model to a fine spatial resolution (0.25° × 0.25°) under 2 Intergovernmental Panel on Climate Change Representative Concentration Pathways (RCPs): RCP4.5, a moderate global warming and emission scenario where global warming is between 1.5°C and 2.0°C, and RCP8.5, a high global warming and emission scenario where global warming exceeds 2.0°C. We then estimated the future annual and seasonal ozone-related acute excess mortality attributable to both climate and population changes using cause-specific, age-group-specific, and season-specific concentration-response functions (CRFs). We used Monte Carlo simulations to obtain empirical confidence intervals (eCIs), quantifying the uncertainty in CRFs and the variability across ensemble members (i.e., 3 predictions of future climate and air quality from slightly different starting conditions) of the global model. Estimates of future changes in annual ozone-related mortality are sensitive to the choice of global warming and emission scenario, decreasing under RCP4.5 (-24.0%) due to declining ozone precursor emissions but increasing under RCP8.5 (10.7%) due to warming climate in 2053-2055 relative to 2013-2015. Higher ambient ozone occurs under the high global warming and emission scenario (RCP8.5), leading to an excess 1,476 (95% eCI: 898 to 2,977) non-accidental deaths per year in 2053-2055 relative to 2013-2015. Future ozone-related acute excess mortality from cardiovascular diseases was 5-8 times greater than that from respiratory diseases. Ozone concentrations increase by 15.1 parts per billion (10-9) in colder months (November to April), contributing to a net yearly increase of 22.3% (95% eCI: 7.7% to 35.4%) in ozone-related mortality under RCP8.5. An aging population, with the proportion of the population aged 65 years and above increased from 8% in 2010 to 24%-33% in 2050, will substantially amplify future ozone-related mortality, leading to a net increase of 23,838 to 78,560 deaths (110% to 363%). Our analysis was mainly limited by using a single global chemistry-climate model and the statistical downscaling approach to project ozone changes under climate change.
Our analysis shows increased future ozone-related acute excess mortality under the high global warming and emission scenario RCP8.5 for an aging population in China. Comparison with the lower global warming and emission scenario RCP4.5 suggests that climate change mitigation measures are needed to prevent a rising health burden from exposure to ambient ozone pollution in China.
气候变化可能进一步加剧已经污染严重地区的臭氧污染，导致与臭氧相关的健康负担增加。然而，在中国这个世界上最大的温室气体排放国和人口最多的国家，几乎没有这方面的证据。随着中国人口老龄化，人口规模和年龄标准化死亡率下降，人口变化对与臭氧相关的健康负担的潜在影响尚不清楚。此外，气候变化下与臭氧相关的健康负担的季节性变化知之甚少。我们旨在评估在 2 种气候和排放变化情景以及 6 个人口变化情景下，中国 104 个城市在 21 世纪中叶（2053 年）的未来年度和季节性短期暴露于环境臭氧导致的超额死亡人数。
我们收集了 2013 年 4 月 27 日至 2015 年 10 月 31 日（2013-2015 年）期间中国 104 个城市的历史环境臭氧观测数据、人口变化预测数据和基线死亡率数据，其中包括中国大陆总人口的约 13%。我们使用历史臭氧监测数据，对全球化学气候模型在较粗空间分辨率（2.0°×2.5°）下的未来臭氧预测数据进行了偏差校正和空间降尺度处理，将其空间分辨率细化至 0.25°×0.25°，用于 2 种政府间气候变化专门委员会（IPCC）代表性浓度路径（RCP）情景（RCP4.5 和 RCP8.5），其中 RCP4.5 是一种中度全球变暖排放情景，全球变暖介于 1.5°C 和 2.0°C 之间，RCP8.5 是一种高全球变暖排放情景，全球变暖超过 2.0°C。然后，我们使用特定病因、特定年龄组和特定季节的浓度-反应函数（CRF），估计由于气候和人口变化而导致的未来年度和季节性臭氧相关急性超额死亡人数。我们使用蒙特卡罗模拟获得经验置信区间（eCI），量化 CRF 的不确定性以及全球模型中集合成员之间的变异性（即，未来气候和空气质量的 3 个预测，从略有不同的初始条件开始）。未来与臭氧相关的死亡率变化的估计值对全球变暖排放情景的选择敏感，在 RCP4.5 下（-24.0%）由于臭氧前体排放量下降而减少，但在 RCP8.5 下（10.7%）由于 2053-2055 年相对于 2013-2015 年的气候变暖而增加。在高全球变暖排放情景（RCP8.5）下，环境臭氧浓度更高，导致 2053-2055 年与 2013-2015 年相比每年额外发生 1476 例（95% eCI：898 至 2977）非意外死亡。心血管疾病与臭氧相关的急性超额死亡人数是呼吸道疾病的 5-8 倍。臭氧浓度在较冷的月份（11 月至 4 月）增加 15.1 个十亿分率（10-9），导致 RCP8.5 下与臭氧相关的死亡率每年净增加 22.3%（95% eCI：7.7%至 35.4%）。人口老龄化导致 65 岁及以上人口比例从 2010 年的 8%增加到 2050 年的 24%-33%，这将大大放大未来与臭氧相关的死亡率，导致额外死亡人数增加 23838 至 78560 人（110%至 363%）。我们的分析主要受到使用单一全球化学气候模型和统计降尺度方法来预测气候变化下臭氧变化的限制。
我们的分析表明，在中国人口老龄化的情况下，高全球变暖排放情景 RCP8.5 下未来与臭氧相关的急性超额死亡人数增加。与较低的全球变暖排放情景 RCP4.5 相比，这表明需要采取气候变化缓解措施，以防止中国因暴露于环境臭氧污染而导致健康负担增加。
