Blake, DR

Elliott, SM

Wingenter, OW

Atmospheric Environment

English

Oliver W. Wingenter

Scott M. Elliott

Donald R. Blake

Crossref

New Directions: Restoring the westerly winds in the Southern Hemisphere: Climate’s lever

Wingenter, Oliver W

Elliott, Scott M

Blake, Donald R

eScholarship - University of California

UC IrvineUC Irvine Previously Published WorksTitleNew Directions: Restoring the westerly winds in the Southern Hemisphere: Climate’s leverPermalinkhttps://escholarship.org/uc/item/52750218JournalAtmospheric Environment, 44(31)ISSN1352-2310AuthorsWingenter, Oliver WElliott, Scott MBlake, Donald RPublication Date2010-10-01DOI10.1016/j.atmosenv.2010.05.029Copyright InformationThis work is made available under the terms of a Creative Commons Attribution License, availalbe at https://creativecommons.org/licenses/by/4.0/ Peer reviewedeScholarship.org Powered by the California Digital LibraryUniversity of CaliforniacienceDirectAtmospheric Environment 44 (2010) 3866–3868Contents lists available at SAtmospheric Environmentjournal homepage: www.elsevier .com/locate/atmosenvNew Directions: Restoring the westerly winds in the SouthernHemisphere: Climate’s leverIn recent years, the idea of managing Earth’s radiation budget asa “quick fix” for mitigating some of the effects of climate change hasgarnered much attention in both the peer-reviewed and popularmedia. While we recognize that such geoengineering solutions,even if successful, can only delay global warming, we presenthere some new ideas that we hope will stimulate future research.These ideas are based on findings and techniques described else-where, but we combine them in a novel way so as to presentscenarios for further exploration.The westerly winds in the Southern Hemisphere are an impor-tant force contributing to climate modulation (Toggweiler andRussell, 2008; Anderson et al., 2009). Global warming, combinedwith loss of Antarctic ozone have increased the temperature differ-ence (DT) between the southern mid- and high-latitudes (Shindelland Schmidt, 2004), causing strengthening of the westerly windvelocities and also shifting them w3–4 southward (Fig. 1; SenGupta et al., 2009). Continued climate change is expected to inten-sify these winds (Yin, 2005). The alignment of the westerlies withthe wind-driven Antarctic Circumpolar Current is key to theamount of ocean meridional overturning circulation and in deter-mining the Earth’s climate mode, i.e. glacial versus interglacial(Toggweiler and Russell, 2008; Anderson et al., 2009). Today,w70% of the global wind energy used in ocean overturning circula-tion goes into the Antarctic Circumpolar Current (Wunsch, 1998)and upwelling of warm, salty Circumpolar Deep Water (CDW) isthe chief process for venting deep water.During glacial periods, DT is at a minimum and the westerlies arecloser to the equator having less overlap with the Antarctic Circum-polar Current. This results in decreased Ekman pumping of CDW,which further reduces the flux of CO2 to the atmosphere, coolingthe Earth (Toggweiler and Russell, 2008; Anderson et al., 2009).During these periods, Antarctic sea ice extends much farther northresulting in greater albedo and even less coupling between thewest-erlies and the Antarctic Circumpolar Current (Sen Gupta et al., 2009).Conversely, slight warming, such as that caused in the past bychanges in the Earth’s orbit, can activate the poleward shift of thewesterlies. The greater wind stress acting on the Antarctic Circum-polar Current moves more water northward via Ekman transport.This in turn pulls more CDW to the surface, releasing CO2 into theatmosphere and prompting further warming and upwelling(Toggweiler and Russell, 2008; Anderson et al., 2009).Presently, a portion of this wind-driven upwelling is transportednorth, where it combines with surface water and sinks below theocean mixed layer, sequestering considerable amounts of anthro-pogenic CO2 (Sabine et al., 2004). However, levels of CO2 in thesouthwest Indian Ocean and portions of the Southern Ocean areincreasing faster than they are in the atmosphere, indicating1352-2310/$ – see front matter  2010 Published by Elsevier Ltd.doi:10.1016/j.atmosenv.2010.05.029a reduced ocean CO2 sink that appears to be caused by enhancedCDW upwelling (Metzl, 2009; Takahashi et al., 2009). The portionof upwelled CDW that moves southward supplies heat to Antarcticsea ice, ice shelves, and ice sheets, causing them tomelt, potentiallyaccelerating sea level rise (Walker et al., 2007). During this centuryit is estimated that 25–30% of sea ice volume may be lost due tochanges to the westerly winds (Sen Gupta et al., 2009).In order to address some of the negative consequences ofclimate warming outlined above we propose applying two cloud-brighteningmethods in two separate regions. Limited iron fertiliza-tion (LIF; Wingenter et al., 2007; 2008) would be used for thepurpose of cooling the region south of the westerlies to decreasethe net flux of CO2 out of the Southern Ocean and to protect theice. Cloud brightening just in this region would exacerbate DTand the overlap between the westerlies and the Antarctic Circum-polar Current. To overcome this and restore atmospheric and oceancirculation, greater cooling north of the westerlies by cloud bright-ening would be needed. This can be achieved by injecting sea saltparticles into the lower troposphere (Salter et al., 2008; Raschet al., 2009). Cooling in this region would also result in greaterflux of CO2 into the ocean.The natural sulfur cycle can be enhanced by LIF. In many areas,iron is the key nutrient to ocean productivity (Martin et al., 1990).Iron fertilization experiments in the equatorial Pacific (Turneret al., 1996) and Southern Ocean (Turner et al., 2004; Wingenteret al., 2004) have shown that trace amounts of iron promote phyto-plankton growth producing large amounts of dimethyl sulfide(DMS). Isoprene production was also greatly enhanced during theSouthern Ocean Iron Enrichment Experiments (SOFeX; Wingenteret al., 2004). In the troposphere, DMS and isoprene oxidation prod-ucts can add to, or produce, new aerosol particles which can growto cloud condensation nuclei (CCN), increasing cloud reflectivityand cooling the region (O’Dowd and De Leeuw, 2007; Wingenteret al., 2007, 2008). Cloud brightening and significant cooling couldalso hypothetically be achieved by a second method; injectingmicron-size sea salt aerosols from ships such as those describedby Latham and coworkers (Salter et al., 2008).Specifically, we propose to apply iron in narrow strips (a few kmwide) orthogonal to the prevailing winds (Fig. 1) to 7% of the mixedlayer of the Southern Ocean to the south of the westerlies betweenabout 55 and 60S (Fig. 1). Iron concentrations in the strips wouldbe increased from w0.2 nM (nanomolar; 109 M) to 1.2 nM, thenallowed to dilute by a factor of 3, as occurred during SOFeX(Coale et al., 2004), to an area ofw20% of this 5 latitude band. Stripapplication should lead to a more even dispersion of DMS andisoprene and may yield greater particle production, compared tofertilizing one large area. We estimate that this iron applicationFig. 1. November through March composites surface vector winds over the Southern Ocean. Contours indicate wind speed (ms1) and arrows direction. A) is averaged over 1999–2008 and B) 1949–1958. Data from NCEP NCAR Reanalysis (Kalnay et al., 1996). Application of a trace amount of iron in narrow strips between 55 and 60S is proposed.O.W. Wingenter et al. / Atmospheric Environment 44 (2010) 3866–3868 3867would increase the DMS flux by about 80% and would translate toan increase in CCN of about 40% if confined to this latitude band(Ayers et al., 1997; Vallina et al., 2007). Assuming uniform polewarddilutionwe estimate an average increase in CCN of 10%, resulting inincreased cloud albedo (Seinfeld and Pandis, 2006). If the areawerecompletely covered with low altitude clouds having no overlapwith higher clouds, we would expect an increase in reflectionof w2.2 Wm2 (assuming 300 Wm2 of incoming solar radiation)for the area south of 55S. Allowing for less than complete lowcloud coverage and overlap reduces this estimate to about 1Wm2, which would cool the Southern Ocean region south of thewesterlies by w0.7 C. The low pressures south of the westerlies(Gillett and Thompson, 2003) and prevailing winds (Fig. 1) shouldhelp contain the CCN and precursors from advecting northwards.However, even in this case, weather systems will transport someof the additional DMS and particles away to the north, limitingcooling south of 55S to about 0.5 C. Ship usage would cost about$100–200 M for applications during late Spring, Summer and earlyFall, with additional costs for in situ and satellite monitoring,modeling studies and scientific oversight.North of the prevailing winds injection of sea salt may be able tocool the mid-latitude region by an additional 0.5 C, compared tothe high-latitudes, in order to decrease DT and shift the westerliesnorthward. If control of new particle production via LIF proves to beinsufficient at high latitude, then sea salt injections may be neededthere as well. Using either method, the amount of cooling can bemonitored from the surface and space. The extra production ofCCN could be halted almost immediately if some unforeseen conse-quence should occur. The CCN concentrations would return to theirprevious value within about a month. Rewarming of the regionwould take longer.The cloud brightening techniques described above could also beused with other geoengineering methods proposed to restoreclimate. For example, certain stratospheric solar radiation manage-ment proposals may aggravate the southward shift of thewesterlies(Tilmes et al., 2008). Any such shift may be headed off by includingcloud brightening as part of the overall strategy.We have described new climate intervention ideas that couldrestore several aspects of climate by cooling the Southern Oceanregion and decreasing the temperature difference between thesouthern mid- and high-latitudes. However, the risks and benefitscannot be adequately assessed until extensive research has beendone. Further development of fully-coupled biogeochemical generalcirculation models are needed. If LIF were to be used, extensive field,laboratory and modeling experiments would be required to deter-mine its impact on ecosystems, trace gas production and gas-to-particle-albedo processes. Discussion of errors and unintendedconsequences associated with LIF can be found in previous work(Wingenter et al., 2007, 2008). Our treatment of aerosols, CCN andalbedo does not include other potentially important effects such aschanges in cloud lifetime and moisture. These impacts are discussedin Rasch et al. (2009) and references therein. However, these factorsmay be less important for LIF because it would require only a rela-tively modest 10% increase in CCN. Fully functional vehicles whichcan generate micron-sized sea salt aerosols need to be built and fieldtested under conditions expected in the Southern Ocean. The impactof full-scale iron fertilization for the purpose of CO2 sequestrationmay, unintentionally, over-cool a region and could negatively disruptocean and atmospheric circulation. Geoengineering, if successful,can only delay global warming. Emissions of greenhouse gasesmust be controlled to avert catastrophic climate change.AcknowledgmentsThis paper benefitted greatly from comments by Nicola Blake,Isobel Simpson, Jeff Altig and two anonymous reviewers. We thankEdie Steinhoff for her help with the graphics.ReferencesAnderson, R.F., Ali, S., Bradtmiller, L.I., Nielsen, S.H.H., Fleisher, M.Q., Anderson, B.E.,Burckle, L.H., 2009. 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Marine aerosol production: a review of thecurrent knowledge. Phil. Trans. R. Soc. A 356, 1753–1774.Rasch, P.J., Latham, J., Chen, C.-C., 2009. Environ. Res. Lett. 4. doi:10.1088/1748-9326/4/4/045112.Sabine, C.L., et al., 2004. The oceanic sink for anthropogenic CO2. Science 305, 367–371.Salter, S., Sortino, G., Latham, J., 2008. Sea-going hardware for the cloud albedomethod of reversing global warming. Phil.Trans. R. Soc. A 366, 2989–4006.O.W. Wingenter et al. / Atmospheric Environment 44 (2010) 3866–38683868Seinfeld, J.H., Pandis, S.N., 2006. Atmospheric Chemistry and Physics: From AirPollution to Climate Change, second ed. J. Wiley, New York, pp. 1083–1084.Sen Gupta, A., et al., 2009. Projected changes to the southern hemisphere ocean andsea ice in the IPCC AR4 climate models. J. Clim. 22, 3047–3078.Shindell, D.T., Schmidt, G.A., 2004. Southern hemisphere climate response to ozonechanges and greenhouse gas increases. Geophys. Res. Lett. 31, L18209.Takahashi, T., et al., 2009. Climatological mean and decadal change in surfaceocean pCO2, and net sea–air CO2 flux over the global oceans. Deep-Sea Res.II 56, 554–577.Tilmes, S., Müller, R., Salawitch, R., 2008. The sensitivity of polar ozone depletion toproposed geoengineering schemes. Science 320, 1201. doi:10.1126/science.1153966.Toggweiler, J.R., Russell, J.L., 2008. Ocean circulation in a warming climate. Nature451, 286–288.Turner, S.M., Nightingale, P.D., Spokes, L.J., Liddicoatt, M.I., Liss, P.S., 1996. Increaseddimethyl sulphide concentrations in sea water from in situ enrichment. Nature383, 513–517.Turner, S.M., Harvey, M.J., Law, C.S., Nightingale, P.D., Liss, P.S., 2004. Iron inducedchanges in oceanic sulfur biogeochemistry. Geophys. Res. Lett. 31, L14307.Vallina, S.M., Simo, R., Gasso, S., de Boyer-Montegut, C., del Rıo, E., Jurado, E.,Dachs, J., 2007. Analysis of a potential “solar radiation dose–dimethylsulfide–cloud condensation nuclei” link from globally mapped seasonal correlations.Global Biogeochem. Cycles 21, GB2004.Walker, D.P., Brandon, M.A., Jenkins, A., Allen, J.T., Dowdeswell, J.A., Evans, J., 2007.Oceanic heat transport onto the Amundsen sea shelf through a submarineglacial trough. Geophys. Res. Lett. 34 L02602.Wingenter, O.W., Elliott, S.M., Blake, D.R., 2007. New directions: enhancing thenatural sulfur cycle to slow global warming. Atmos. Environ. 41, 7373–7375.Wingenter, O.W., Elliott, S.M., Blake, D.R., 2008. Authors response to the abovecomment by M. Vogt et al. on “New directions: enhancing the natural sulfurcycle to slow global warming”, Atmos. Environ. 42, 4806–4809.Wingenter, O.W., Haase, K.B., Strutton, P., Friedrich, G., Meinardi, S., Blake, D.R.,Rowland, F.S., 2004. Changing concentrations of CO, CH4, C5H8, CH3Br, CH3I,and dimethyl sulfide during the southern ocean iron enrichment experiments.Proc. Natl. Acad. Sci. 101, 8537–8541.Wunsch, C., 1998. The work done by the wind on the oceanic general circulation.J. Phys. Oceangr. 28, 2332–2340.Yin, J.H., 2005. A consistent poleward shift of the storm tracks in simulations of 21stcentury climate. Geophys. Res. Lett. 32, L18701. doi:10.1029/2005GL023684.Oliver W. Wingenter*Geophysical Research Center and the Department of Chemistry,New Mexico Institute of Mining and Technology,Socorro, NM 87801, USA* Corresponding author. Tel.: þ1 505 681 8768.E-mail address: oliver@nmt.eduScott M. ElliottClimate Ocean Sea Ice Modeling Project,Los Alamos National Laboratory,NM 87545, USADonald R. BlakeDepartment of Chemistry and the Earth System Science,University of California, Irvine, CA 92697, USA16 January 2010

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New Directions: Restoring the westerly winds in the Southern Hemisphere: Climate's lever

New Directions: Restoring the westerly winds in the Southern Hemisphere: Climate's lever

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