Estimates of ozone return dates from Chemistry-Climate Model Initiative simulations
Estimates of ozone return dates from Chemistry-Climate Model Initiative simulations
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DOI：
10.5194/acp-18-8409-2018
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发表时间：
2018-06-15
影响因子：
6.3
通讯作者：
Zeng, Guang
中科院分区：
文献类型：
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作者：
Dhomse, Sandip S.;Kinnison, Douglas;Zeng, Guang
我们分析了为化学-气候模式倡议(CCMI)进行的模拟，以估计由人为平流层氯和溴造成的平流层臭氧层消耗的回归日期。我们考虑了来自20个模型的155个模拟，包括一系列考察气候变化对臭氧恢复的影响的敏感性研究。对于控制模拟(不受分析气象学的限制)，绝对臭氧层柱的预测有很大的差异(全球平均值为+/-20DU)。因此，模型结果需要针对历史数据的偏差进行调整。此外，需要对模型结果中的年际变化进行平滑处理，以便对臭氧回归日期的范围提供一个合理狭窄的估计。与以前的研究一致，但在这里，对于代表浓度路径(RCP)为6.0，这些新的CCMI模拟预测，全球柱臭氧总量将在2049年恢复到1980年的值(1西格玛不确定性为2043-2055)。在南半球中纬度地区，臭氧柱预计将在2045年(2039-2050年)恢复到1980年的值，而在北半球中纬度地区，臭氧将在2032年(2020-2044年)恢复到1980年的水平。在极地地区，南极的回归日期是10月的2060(2055-2066)，北极的回归日期是3月的2034(2025-2043)。北半球较早的回归日期反映了对动力变化的较大敏感性。我们对回归日期的估计比2014年臭氧评估中提出的估计晚了大约5-17年，这取决于该地区，以前的最佳估计经常超出我们的不确定性范围。在热带地区，只有大约一半的模型预测臭氧将在2040年左右恢复到1980年的值，而另一半的模型没有达到1980年的值。到21世纪末，所有模式都显示出热带大气臭氧总量的负趋势。CCMI模型在模拟平流层氯和溴的时间演变时基本一致，这是臭氧损失和恢复的主要驱动因素。然而，有一些离群值表明，臭氧恢复的多模式平均结果并没有受到尽可能严格的限制。在整个平流层，臭氧返回值的扩散在模型之间往往与无机氯返回到1980年值的扩散相关。在平流层上层，温室气体引起的降温使气候回归的速度加快了约10-20年。在较低的平流层，对于柱状物来说，臭氧和氯的回归日期的时间有更直接的联系，特别是对于南极的大消耗。模型之间对柱臭氧总量的比较受到对同一情景下对流层臭氧演变的不同预测的影响，这可能是由于对流层化学处理的不同所致。因此，对于许多情况，只能对平流层臭氧层柱而不是总臭氧层柱得出明确的结论。正如以前的研究指出的那样，臭氧恢复的时间受到N2O和CH4演变的影响。然而，与内部模型可变性相比，在这里分析的模拟中量化影响是有限的，因为这些实验可用的实现很少。RCP 6.0中给出的N2O的大幅增加将全球臭氧回归延长了大约15年，相对于1960年固定的N2O丰度，主要是因为它允许热带柱状臭氧被消耗。与RCP 6.0相比，RCP 8.5情景中给出的CH4的大幅增加也将臭氧回归延长了大约15年，同样主要是通过其对热带地区的影响。总体而言，我们对臭氧回归日期的估计是不确定的，因为未来情景的不确定性，特别是温室气体的不确定性，以及模型中的不确定性。情景的不确定性在短期内很小，但随着时间的推移而增加，并在本世纪末变得更大。与影响臭氧回收的众所周知的过程有关的一些模型-模型差异仍然存在。需要继续努力确保用于评估目的的模型准确地反映平流层化学和臭氧消耗物质的规定情景，并且只有这些模型才用于计算回归日期。对于未来对二氧化碳、CH4和N2O对平流层柱臭氧返回日期的单一强迫或综合影响的评估，这项工作表明，对于每个已建立的参与模式的每个情景，更重要的是有多个成员(至少三个)集合，而不是大量的单独模式。
We analyse simulations performed for the Chemistry-Climate Model Initiative (CCMI) to estimate the return dates of the stratospheric ozone layer from depletion caused by anthropogenic stratospheric chlorine and bromine. We consider a total of 155 simulations from 20 models, including a range of sensitivity studies which examine the impact of climate change on ozone recovery. For the control simulations (unconstrained by nudging towards analysed meteorology) there is a large spread (+/- 20DU in the global average) in the predictions of the absolute ozone column. Therefore, the model results need to be adjusted for biases against historical data. Also, the interannual variability in the model results need to be smoothed in order to provide a reasonably narrow estimate of the range of ozone return dates. Consistent with previous studies, but here for a Representative Concentration Pathway (RCP) of 6.0, these new CCMI simulations project that global total column ozone will return to 1980 values in 2049 (with a 1 sigma uncertainty of 2043-2055). At Southern Hemisphere mid-latitudes column ozone is projected to return to 1980 values in 2045 (2039-2050), and at Northern Hemisphere mid-latitudes in 2032 (2020-2044). In the polar regions, the return dates are 2060 (2055-2066) in the Antarctic in October and 2034 (2025-2043) in the Arctic in March. The earlier return dates in the Northern Hemisphere reflect the larger sensitivity to dynamical changes. Our estimates of return dates are later than those presented in the 2014 Ozone Assessment by approximately 5-17 years, depending on the region, with the previous best estimates often falling outside of our uncertainty range. In the tropics only around half the models predict a return of ozone to 1980 values, around 2040, while the other half do not reach the 1980 value. All models show a negative trend in tropical total column ozone towards the end of the 21st century. The CCMI models generally agree in their simulation of the time evolution of stratospheric chlorine and bromine, which are the main drivers of ozone loss and recovery. However, there are a few outliers which show that the multi-model mean results for ozone recovery are not as tightly constrained as possible. Throughout the stratosphere the spread of ozone return dates to 1980 values between models tends to correlate with the spread of the return of inorganic chlorine to 1980 values. In the upper stratosphere, greenhouse gas-induced cooling speeds up the return by about 10-20 years. In the lower stratosphere, and for the column, there is a more direct link in the timing of the return dates of ozone and chlorine, especially for the large Antarctic depletion. Comparisons of total column ozone between the models is affected by different predictions of the evolution of tropospheric ozone within the same scenario, presumably due to differing treatment of tropospheric chemistry. Therefore, for many scenarios, clear conclusions can only be drawn for stratospheric ozone columns rather than the total column. As noted by previous studies, the timing of ozone recovery is affected by the evolution of N2O and CH4. However, quantifying the effect in the simulations analysed here is limited by the few realisations available for these experiments compared to internal model variability. The large increase in N2O given in RCP 6.0 extends the ozone return globally by similar to 15 years relative to N2O fixed at 1960 abundances, mainly because it allows tropical column ozone to be depleted.The effect in extratropical latitudes is much smaller. The large increase in CH4 given in the RCP 8.5 scenario compared to RCP 6.0 also lengthens ozone return by similar to 15 years, again mainly through its impact in the tropics. Overall, our estimates of ozone return dates are uncertain due to both uncertainties in future scenarios, in particular those of greenhouse gases, and uncertainties in models. The scenario uncertainty is small in the short term but increases with time, and becomes large by the end of the century. There are still some model-model differences related to well-known processes which affect ozone recovery. Efforts need to continue to ensure that models used for assessment purposes accurately represent stratospheric chemistry and the prescribed scenarios of ozone-depleting substances, and only those models are used to calculate return dates. For future assessments of single forcing or combined effects of CO2, CH4, and N2O on the stratospheric column ozone return dates, this work suggests that it is more important to have multi-member (at least three) ensembles for each scenario from every established participating model, rather than a large number of individual models.