Editorial pubs.acs.org/CR
Role of Chemistry in Earth’s Climate some form in the atmosphere by a series of reactions initiated by oxidation of different volatile gases. Ozone is another greenhouse gas, produced by the troposphere in chemical reactions that consume emitted volatile hydrocarbons and use nitrogen oxides as a catalyst. Finally, most emissions are removed from the atmosphere by the oxidants in the atmosphere such as such as OH radicals, nitrate radicals, and ozone; these determine the crucial “cleansing” capacity of the atmosphere.3 Evidently, chemically active agents are a large part of the influence of human activities on climate. (2) The impact of climate change on Earth is multifaceted. The most notable changes are rise in sea level, changes in precipitation, drought, extreme weather events, and more. Chemistry is greatly involved in shaping many of these impacts. For example, aerosols are at the heart of radiative forcing and the precipitation issues. Other key impacts occur through changes in the atmospheric chemical composition, for example deterioration of air quality, changes in the oxidative capacity of the atmosphere, and possible changes in the atmospheric circulation patterns. (3) Climate change, related to non-CO2 gases and aerosols, is very dependent on chemical processes.4 The contribution of an emission that leads to greenhouse gases or aerosols, and thus alters the radiation balance of the Earth system, depends on chemical properties. Key questions regarding each emission include: how long does the emitted species stay in the atmosphere before it is removed or transformed to another species, where and how strongly does it (or products of its atmospheric reactions) absorb or scatter UV, visible, or infrared radiation, and how does it modify the atmospheric lifetime and properties of other chemicals in the atmosphere? (4) Chemistry plays important roles in any potential climate change mitigation and adaptation strategies, including intentional human intervention efforts, commonly termed as “geoengineering” or “solar radiation management”. For the above reasons, it is abundantly clear that chemistry plays a pivotal role in Earth’s climate system. The essence of the role of chemistry in climate is captured on the cover of this issue. The Earth system is highly coupled. The coupling means that the different environmental issues noted earlier are often connected. For example, fossil fuel burning is clearly at the heart of anthropogenic climate change and it is also the pivotal issue for air quality. So, solutions to climate change are intimately connected with air quality issues (A few papers in this volume cover such issues, e.g., Ariya et al., Zhang et al., Von Schneidemesser et al., and Pusede et al.). Ozone layer depletion is caused by chlorinated and brominated fluorocarbons (and related chemicals). These ozone-depleting chemicals (ODSs) are not only destructive to the ozone layer but are also potent greenhouse gases. Therefore, the control on ODSs has not only helped heal the ozone layer but also greatly helped climate (Burkholder et al. discuss the chemical degradation of ODSs).
Human activities are known to affect our environment. Major 20th and 21st century environmental issues include deterioration of air quality (fog, photochemical production of smog and tropospheric ozone, mercury pollution, etc.), poor water quality (due to release of pollutants to water bodies), vast pesticide usage, acid precipitation (from coal combustion that leads to SO2 and thus sulfuric acid), ozone layer depletion (due to use of ozone depleting substances such as chlorofluorocarbons), etc. Some of these issues have been successfully tackled through national and regional legislations, international agreements, provision of alternatives, and/or changes in peoples’ expectations and behavior. However, climate change due to emission of anthropogenic greenhouse gases and other chemicals into the atmosphere is now recognized to be one of the major asyet-unsolved challenges facing humanity in the coming decades and centuries. The impacts of anthropogenic climate change are slow in coming, it is sometimes difficult to see the signal above natural variability, and impacts are coupled to some of the most basic needs of society, such as energy production and utilization, food security, and infrastructure. Therefore, it is a very challenging problem for society. After all, when it is difficult to see changes above variability and noise, it is hard to take action, especially when the results may be visible only in the distant future. Furthermore, the issue requires making choices between very important social behavior and economic factors. Yet, it is clearer than ever that anthropogenic climate change is an issue to be reckoned with. The largest contributor to the predicted anthropogenic climate change arises from the burning of fossil fuels that generates carbon dioxide, a greenhouse gas.1 Increases in CO2 concentration will not only influence climate but also the acidity of the oceans.2 While acid−base equilibria and their changes are at the heart of the latter issue (a topic not covered in this special issue), in the atmosphere, CO2 is not very chemically active. Therefore, one could wonder: what is the role of chemistry in Earth’s climate system, especially the human-induced climate change? The answer to this question is multipronged. (1) In addition to CO2, there are many other emissions of chemically active species that directly or indirectly force Earth’s climate. They include CH4, halocarbons, N2O, nonmethane hydrocarbons (NMHC), and nitrogen oxides. Together, these non-CO2 emissions contribute almost as much as human-produced CO2 to today’s climate forcing, as measured using the metric of radiative forcing (see article by Ravishankara et al.); the current radiative forcing by CO2 is estimated1 to be about 1.68 Wm−2, while the non-CO2 emissions contribute about 1.65 Wm−2). Unlike the greenhouse gases, aerosols (a suspension of liquid or solid matter in the air) and clouds are expected to exert a global negative forcing and they are currently estimated to be offsetting positive forcing by the greenhouse gases by as much as 50% of the forcing by CO2. However, there is a large uncertainty about the cooling and heating effects of different aerosol types such as soot, dust, and absorbing organic molecules. Some of the aerosols are emitted directly, while © 2015 American Chemical Society
Special Issue: 2015 Chemistry in Climate Published: May 27, 2015 3679
DOI: 10.1021/acs.chemrev.5b00226 Chem. Rev. 2015, 115, 3679−3681
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“win−win strategies” for the multiple issues that are involved. At least, one needs to avoid “win−lose” choices where solutions to one issue either exacerbate another issue or create a new problem. Thus, understanding of chemical changes will continue to play a major role in better understanding and predicting of climate change, and providing solutions to anthropogenic climate change.
Tropospheric ozone itself is a greenhouse gas, and its changes influence climate. Chemical transformations of hydrocarbons (both natural and anthropogenic) are key to accounting for present levels and predicting future levels of ozone in the troposphere (Papers by Nozière et al., Mellouki et al., Carpenter and Nightingale, Simpson et al., Vereecken et al., and Pusede et al. discuss identification, emissions, and chemical transformations of chemicals in the atmosphere). Conversely, climate change will change ozone levels in the troposphere and, thus, play an important role in affecting air quality regionally and globally. Carbon dioxide has a very complex and long lifetime in the atmosphere. It persists for centuries and its effects also persist for a very long time.5 In contrast, the chemically active reactive species have shorter lifetimes. Therefore, there is more immediate relief for the climate system when such emissions are reduced. Consequently, there is now a focus on short-lived climate forcers in climate change mitigation approaches; this issue further highlights the importance of chemistry in the climate system today. One of the major issues that has emerged over the past decade is the large role played by aerosols in the climate system via interaction with incoming sunlight, modifying chemical composition, and influencing precipitation and clouds and, thus, Earth’s radiation balance. This is particularly important since aerosols are currently thought to partially offset the positive climate forcing by greenhouse gases. Aerosols are complexthey come in different sizes, chemical composition, phases, and properties. In addition, they are implicated in adverse health effects. They also play important roles in transforming some chemicals in the atmosphere. Their origins are diverse but are partly connected with combustion, the same source as for CO2. However, aerosols are thought of mostly as pollutants that influence air quality. Thus, the policy instruments for dealing with aerosols are different from those for greenhouse gases. The issues related to aerosols add further layers of complexity in causes as well as in solutions. Suffice it to say, aerosols are one of the hot topics in atmospheric chemistry today. This is richly represented in this thematic issue with a large number of articles covering various aspects of this issue (Bilde et al., Ervens, Farmer et al., George et al., Herrmann et al., Laskin et al., Quinn et al., and Moise et al. discuss various aspects of the role of aerosols and condensed matter in the atmosphere). The complexity of aerosols has perplexed scientists. Yet, it is important to understand and predict the influence of aerosols on climate as well as its influences on related issues such as health, melting of snow and ice by black carbon, etc. (Pöschl and Shiraiwa discuss some aspects of health and climate impacts of aerosols). Lastly, higher parts of the atmosphere, the ionosphere and the mesosphere, hold very little mass but still respond to climate change. Chemical aspects of these regions are also described in this thematic issue (see Plane et al. and Shuman et al.). There are a myriad of couplings in the climate system, some of which were noted above. Suffice to say, human actions to control one environmental issue will undoubtedly influence another. Indeed, some actions have clear impacts on multiple issues, such as climate change and air quality. (See articles by Heald and Spracklen, Pusede et al., and von Schneidermesser et al.) It is very desirable that actions taken by society will have positive effects on climate and the environmentthe so-called
A. R. Ravishankara* Colorado State University, USA
Yinon Rudich* Weizmann Institute, Israel
John A. Pyle* Cambridge University, UK National Centre for Atmospheric Science (NCAS)
AUTHOR INFORMATION Corresponding Authors
*A. R. Ravishankara, E-mail:
[email protected]. Phone: +19704912876. *Y. Rudich, E-mail:
[email protected]. Phone: + 972 8 934 4237. *J. A. Pyle, E-mail:
[email protected]. Phone: +44 (01223) 336473. Notes
Views expressed in this editorial are those of the author and not necessarily the views of the ACS. Biographies
A. R. Ravishankara is an atmospheric chemist. He obtained his Ph.D. from the University of Florida, Gainesville, FL, in physical chemistry. After one year of postdoctoral work at University of Maryland, where he entered the field of atmospheric chemistry, he moved to Georgia Institute of Technology for 8 years and then to National Oceanic and Atmospheric Administration for 30 years. He moved to Colorado State University in 2014. He has worked over the past thirty-eight years on the chemistry of the Earth’s atmosphere as it relates to stratospheric ozone depletion, climate change, regional air quality, and their intersections. He has authored more than 350 peer-reviewed papers. His measurements in the laboratory and in the atmosphere have contributed to deciphering the ozone layer depletion, including the ozone hole; to development of substitutes for ozone depleting substances; to quantifying the role of chemically active species on climate; and to advancing understanding of the formation, removal, and properties of pollutants. He has served or is serving on various editor boards and was an editor of Geophysical Research Letters. Ravishankara is a member of the U.S. National Academy of Sciences. Other recognitions include his election as a Fellow of the American 3680
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since 2007 has been the 1920 Professor of Physical Chemistry. He is a Professorial Fellow at St. Catharine’s College. He has been a codirector of NERC’s National Centre for Atmospheric Science (NCAS), where he is now the Chief Scientist. His research focuses on the numerical modeling of atmospheric chemistry. Problems involving the interaction between chemistry and climate have been addressed; these range from stratospheric ozone depletion to the changing tropospheric oxidizing capacity and have included the environmental impact of aviation, land use change, biofuel technologies, and the hydrogen economy. He has studied palaeochemistry problems as well as the projected atmospheric composition changes during the current century. He has published more than 250 peer-reviewed papers. He played a major role in building an EU stratospheric research program in the 1990s, coordinating several major field campaigns. He has contributed to all the WMO/UNEP assessments on stratospheric ozone since the early 1980s and is now one of the four international Co-Chairs on the Scientific Assessment Panel, responsible for these assessments. He was a convening lead author in the IPCC Special report “Safeguarding the ozone layer and the global climate system”, published in 2006. His work on stratospheric ozone was recognized by NERC’s International Impact Award and Overall Impact Award in 2015, jointly with Neil Harris. He was elected a Fellow of the Royal Society in 2004 and an AGU Fellow in 2011. He was awarded the Cambridge ScD degree in 2012. Other honors and awards include membership of Academia Europaea (1993), Royal Society of Chemistry (Interdisciplinary award, 1991, and John Jeyes lectureship, 2008), and the Royal Meteorological Society Adrian Gill Prize, in 2004.
Geophysical Union, Fellow of the American Association for the Advancement of Science, Fellow of the United Kingdom Royal Society of Chemistry, recipient of the Polanyi Medal and Centenary lectureship of the Royal Society of Chemistry, the U.S. Environmental Protection Agency’s Stratospheric Ozone Protection Award, the Department of Commerce Silver Medal, and the U.S. Presidential Rank Award. Of relevance to this article, Ravishankara is a co-Chair of the Scientific Assessment Panel of the Montreal Protocol that deals with the ozone layer and depleting substances, a member of the Scientific Advisory Panel for the Climate Clean Air Coalition (an UN organization), and the Chair of the Board on Atmospheric Science and Climate of the US National Academy of Science. He has also led or authored numerous international and national assessment reports related to this article. Over the past decade, in addition to atmospheric chemistry research, he is interested in taking scientific information to decision-makers.
REFERENCES (1) IPCC. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change; Cambridge University Press: Cambridge, United Kingdom, and New York, NY, USA, 2013. (2) Doney, S. C.; Fabry, V. J.; Feely, R. A.; Kleypas, J. A. Annu. Rev. Mar. Sci. 2009, 1, 169. (3) Prinn, R. G. Annu. Rev. Environ. Res. 2003, 28, 29. (4) Ravishankara, A. R. Faraday Discuss. 2005, 130, 9. (5) Solomon, S.; Plattner, G.-K.; Knutti, R.; Friedlingstein, P. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 1704.
Yinon Rudich received his B.Sc. degree from Ben Gurion University and M.Sc. and Ph.D. degrees in chemical physics from the Weizmann Institute. Following postdoctoral work at the National Oceanic and Atmospheric Administration, he joined the Weizmann Institute of Science, where he is presently a Professor at the Department of Earth and Planetary Sciences. His research interests include the chemistry and physical properties of organic aerosols, ice nucleation, bioaerosols, and the health effects of atmospheric aerosols. Other interests include heterogeneous atmospheric chemistry and development of new analytical techniques for characterization of atmospheric particles and bioaerosols. He was editor of the Journal of Geophysical Research Atmospheres.
John Pyle obtained a B.Sc. in Physics at Durham. His D.Phil. was at Oxford, where he helped to develop a numerical model for stratospheric ozone studies. After a period at the Rutherford Appleton Laboratory, he moved to a lectureship at Cambridge University in 1985. In 2000 he was appointed Professor of Atmospheric Science and 3681
DOI: 10.1021/acs.chemrev.5b00226 Chem. Rev. 2015, 115, 3679−3681
