Understanding the Direct and Ozone-Mediated Impacts of (CO2) and Ozone Depleting Substances (ODS) on the Climate System

臭氧空洞和温室气体引起的全球变暖是截然不同的环境问题。臭氧空洞很重要，因为平流层臭氧的减少导致到达地面的有害紫外线辐射增加。臭氧层空洞中的臭氧损失是由在喷雾罐和冷却设备等特定应用中使用的少量消耗臭氧物质（ODS，主要是氯氟化碳）造成的。另一方面，全球变暖是由整个世界经济排放的温室气体的吸热效应引起的，主要是燃烧化石燃料所排放的二氧化碳。尽管全球变暖和臭氧空洞之间有明显的区别，但有重要的物理途径将两者联系起来。一是大多数消耗臭氧层物质也是温室气体。臭氧消耗物质的浓度与二氧化碳相比微不足道，但它们作为红外辐射吸收剂的效率是二氧化碳的数千倍，因此它们的吸热作用是巨大的。另一个联系是，二氧化碳的增加会改变平流层中臭氧的数量和分布。虽然二氧化碳使对流层变暖，但却使平流层变冷，这是由于它们相反的温度分布造成的差异（对流层高处冷，下层暖，平流层反之）。较低的平流层温度可以通过降低消耗臭氧的化学反应速率来增加臭氧浓度。但是二氧化碳的增加也会导致平流层翻转环流的加速，这反过来又会减少平流层臭氧的寿命。这项工作探讨了二氧化碳和消耗臭氧层物质对气候的影响，认识到它们既直接影响气候，也通过对平流层臭氧的影响影响气候。除了全球温度外，该研究还考虑了对海面温度、海平面压力、急流风速和其他变量的区域影响。例如，初步工作表明，耗散物质造成的温室增温在南北太平洋的亚热带地区最为严重，这可能是耗散物质地理分布不均匀的结果。进一步的考虑是，消耗臭氧层物质可以作为一种强大的温室气体直接影响气候，也可以通过臭氧损失引起的气候变化间接影响气候。例如，PI和其他人之前的工作表明，臭氧空洞已经影响了南半球的风、温度和降水。这项工作还研究了由于二氧化碳增加而导致的平流层臭氧的变化。该项目的主要研究工具是由国家大气研究中心开发的全大气群落气候模型。由于臭氧消耗和全球变暖的社会影响，这项工作具有更广泛的影响。解决这些影响的努力将受益于对所涉及过程的更好的物理理解。由于苏黎世瑞士联邦理工学院的研究人员的参与，这项工作还促进了国际科学合作。该项目还为一名研究生和一名博士后研究员提供支持和培训，从而促进该研究领域的未来劳动力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The ozone hole and greenhouse gas-induced global warming are distinct environmental problems. The ozone hole matters because reductions in stratospheric ozone lead to increases in harmful ultraviolet radiation reaching the surface. The loss of ozone in the hole is caused by a small set of ozone depleting substances (ODS, primarily chlorofluorocarbons) used in a specific set of applications such as spray cans and cooling equipment. Global warming, on the other hand, is caused by the heat-trapping effect of greenhouse gases emitted throughout the world economy, principally the carbon dioxide (CO2) emitted in the burning of fossil fuels.Despite the clear distinction between global warming and the ozone hole there are important physical pathways that link the two. One is that most ODS are also greenhouse gases. ODS concentrations are minuscule compared to CO2 but they are thousands of times more effective as absorbers of infrared radiation, thus their heat-trapping effect is substantial. Another connection is that CO2 increases can change the amount and distribution of ozone in the stratosphere. Although CO2 warms the troposphere it cools the stratosphere, a difference caused by their opposite temperature profiles (cold aloft, warm below in the troposphere and vice versa in the stratosphere). Cooler stratospheric temperatures can increase ozone concentrations by reducing the reaction rates for ozone-depleting chemistry. But a CO2 increase can also cause a speed-up of the stratospheric overturning circulation, which in turn decreases the lifetime of stratospheric ozone.This work explores the climatic effects of CO2 and ODS, recognizing that they affect climate both directly and through their impact on stratospheric ozone. In addition to global temperature the study considers regional influences on sea surface temperature, sea level pressure, jet stream wind speed, and other variables. Preliminary work suggests, for example, that the greenhouse warming due to ODS is greatest in the subtropics of the North and South Pacific, presumably as a consequence of the uneven geographical distribution of ODS. A further consideration is that ODS can affect climate either directly, as a powerful greenhouse gas, or indirectly through the changes in climate induced by ozone loss. For example, previous work by the PI and others shows that the ozone hole has affected the winds, temperature, and precipitation of the Southern Hemisphere. The work also examines changes in stratospheric ozone due to CO2 increases. The primary research tool of the project is the Whole Atmosphere Community Climate Model developed at the National Center for Atmospheric Research.The work has broader impacts due to the societal impacts of ozone depletion and global warming. Efforts to address these impacts will benefit from a better physical understanding of the processes involved. The work also fosters international scientific collaboration given the participation of researchers at the Swiss Federal Institute of Technology in Zurich. The project also provides support and training to a graduate student and a postdoctoral research associate, thereby promoting the future workforce in this research area.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.