HARVARD EPS 5 - Global Warming and Northern Hemisphere Sea Ice Extent

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DOI: 10.1126/science.286.5446.1934 , 1934 (1999); 286Science et al.Konstantin Y. Vinnikov,ExtentGlobal Warming and Northern Hemisphere Sea IceThis copy is for your personal, non-commercial use only.. clicking herecolleagues, clients, or customers by , you can order high-quality copies for yourIf you wish to distribute this article to others. herefollowing the guidelines can be obtained byPermission to republish or repurpose articles or portions of articles (this information is current as of September 30, 2010 ):The following resources related to this article are available online at www.sciencemag.org http://www.sciencemag.org/cgi/content/full/286/5446/1934version of this article at: including high-resolution figures, can be found in the onlineUpdated information and services, http://www.sciencemag.org/cgi/content/full/286/5446/1934#otherarticles, 2 of which can be accessed for free: cites 20 articlesThis article 188 article(s) on the ISI Web of Science. cited byThis article has been http://www.sciencemag.org/cgi/content/full/286/5446/1934#otherarticles 7 articles hosted by HighWire Press; see: cited byThis article has been http://www.sciencemag.org/cgi/collection/atmosAtmospheric Science : subject collectionsThis article appears in the following registered trademark of AAAS. is aScience1999 by the American Association for the Advancement of Science; all rights reserved. The title CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by theScience on September 30, 2010 www.sciencemag.orgDownloaded fromReferences and Notes1. Y.-W. Mo, D. E. Savage, B. S. Swartzentruber, M. G.Lagally, Phys. Rev. Lett. 65, 1020 (1990).2. G. Medeiros-Ribeiro, A. M. Bratkovsky, T. I. Kamins,D. A. A. Ohlberg, R. S. Williams, Science 279, 353(1998).3. T. I. Kamins, E. C. Carr, R. S. Williams, S. J. Rosner,J. Appl. Phys. 81, 211 (1997); M. Tomitori, K. Wa-tanabe, M. Kobayashi, O. Nishikawa, Appl. Surf. Sci.76 –77, 322 (1994).4. J. A. Floro et al., Phys. Rev. B 59, 1990 (1999).5. T. I. Kamins, G. Medeiros-Ribeiro, D. A. A. Ohl-berg, R. S. Williams, J. Appl. Phys. 85, 1159(1999).6. F. M. Ross, J. Tersoff, R. M. Tromp, Phys. Rev. Lett. 80,984 (1998).7. R. M. Tromp, M. Mankos, M. C. Reuter, A. W. Ellis, M.Copel, Surf. Rev. Lett. 5, 1189 (1998).8. Z. Gai, X. Li, R. G. Zhao, W. S. Yang, Phys. Rev. B 57,15060 (1998).9. M. Goryll, L. Vescan, K. Schmidt, S. Mesters, H. Luth,Appl. Phys. Lett. 71, 410 (1997); M. A. Lutz, R. M.Feenstra, P. M. Mooney, J. Tersoff, J. O. Chu, Surf. Sci.316, L1075 (1994).10. R. M. Tromp, F. M. Ross, M. C. Reuter, in preparation.11. M. Zinke-Allmang, L. C. Feldman, M. Grabow, Phys.Rev. B 39, 7848 (1989).12. I. Daruka, J. Tersoff, A.-L. Barabasi, Phys. Rev. Lett. 82,2753 (1999).13. We thank K. Pope for Rutherford backscattering anal-ysis and J. Tersoff for helpful discussions.22 July 1999; accepted 20 October 1999Global Warming and NorthernHemisphere Sea Ice ExtentKonstantin Y. Vinnikov,1* Alan Robock,2Ronald J. Stouffer,3John E. Walsh,4Claire L. Parkinson,5Donald J. Cavalieri,5John F. B. Mitchell,6Donald Garrett,7Victor F. Zakharov8Surface and satellite-based observations show a decrease in Northern Hemi-sphere sea ice extent during the past 46 years. A comparison of these trendsto control and transient integrations (forced by observed greenhouse gases andtropospheric sulfate aerosols) from the Geophysical Fluid Dynamics Laboratoryand Hadley Centre climate models reveals that the observed decrease in North-ern Hemisphere sea ice extent agrees with the transient simulations, and bothtrends are much larger than would be expected from natural climate variations.From long-term control runs of climate models, it was found that the proba-bility of the observed trends resulting from natural climate variability, assumingthat the models’ natural variability is similar to that found in nature, is less than2 percent for the 1978–98 sea ice trends and less than 0.1 percent for the1953–98 sea ice trends. Both models used here project continued decreases insea ice thickness and extent throughout the next century.The cryosphere is an important component ofclimate because of its effect on Earth’s surfacealbedo (1) and its role in reducing the amount ofheat exchanged between the atmosphere andthe ocean (or land) beneath the ice. In particu-lar, sea ice extent has long been recognized asan important indicator of the state of the climatesystem in observational and modeling studies.Early simulations of changes in sea ice cover-age and sea ice thickness associated with globalwarming showed large sea ice reductions (2, 3),but these simulations were not compared withobservations. Observations now span a suffi-ciently long period to show a substantial de-crease of Northern Hemisphere (NH) sea iceduring the past few decades. Here, we use seaice extent in an attempt to detect recent globalclimate change and examine whether it mightbe attributable to anthropogenic causes by com-paring it with model-calculated global warmingtrends and trendlike low-frequency fluctuationsthat appear randomly in very long control runsof the same models.There have been many attempts to useobserved trends in NH sea ice extent as anindicator of global climate change (4 –16 ).Most of these studies show that, on average,the observed NH sea ice extent has beendecreasing during the past few decades. Sat-ellite visible and infrared images, which be-came available in 1966, were the first sourcesof global information on sea ice extent. In1972, the passive microwave satellite sensorwas introduced as an additional source ofinformation on sea ice extent and concentra-tion. Nonsatellite observational records havemany problems; they are generally not verylong, they are not global, and they do notcover the entire year. Very little sea ice coverdata are currently available for 1941– 45.We used the following five sources of ob-servations to determine sea ice extent in theNH: the University of Illinois sea ice group, theRussian Arctic and Antarctic Research Insti-tute, the NOAA Climate Prediction Center, theNorwegian Nansen Environmental and RemoteSensing Center, and the NASA Goddard SpaceFlight Center.The University of Illinois sea ice group hasjust revised and updated its data set (6, 13). Themost reliable data cover the period since 1953.The recent inclusion of data from


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