[geo] A critical evaluation of volcanic cooling
Atmos. Chem. Phys., 13, 3997-4031, 2013 www.atmos-chem-phys.net/13/3997/2013/ doi:10.5194/acp-13-3997-2013 © Author(s) 2013. This work is distributed under the Creative Commons Attribution 3.0 License. An empirical model of global climate – Part 1: A critical evaluation of volcanic cooling T. Canty1, N. R. Mascioli1,*, M. D. Smarte2,**, and R. J. Salawitch1,2,3 1Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD, USA 2Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, USA 3Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA *now at: Department of Earth and Environmental Sciences, Columbia University, New York, NY, USA **now at: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA Abstract. Observed reductions in Earth's surface temperature following explosive volcanic eruptions have been used as a proxy for geoengineering of climate by the artificial enhancement of stratospheric sulfate. Earth cools following major eruptions due to an increase in the reflection of sunlight caused by a dramatic enhancement of the stratospheric sulfate aerosol burden. Significant global cooling has been observed following the four major eruptions since 1900: Santa María, Mount Agung, El Chichón and Mt. Pinatubo, leading IPCC (2007) to state major volcanic eruptions can, thus, cause a drop in global mean surface temperature of about half a degree Celsius that can last for months and even years. We use a multiple linear regression model applied to the global surface temperature anomaly to suggest that exchange of heat between the atmosphere and ocean, driven by variations in the strength of the Atlantic Meridional Overturning Circulation (AMOC), has been a factor in the decline of global temperature following these eruptions. The veracity of this suggestion depends on whether sea surface temperature (SST) in the North Atlantic, sometimes called the Atlantic Multidecadal Oscillation, but here referred to as Atlantic Multidecadal Variability (AMV), truly represents a proxy for the strength of the AMOC. Also, precise quantification of global cooling due to volcanoes depends on how the AMV index is detrended. If the AMV index is detrended using anthropogenic radiative forcing of climate, we find that surface cooling attributed to Mt. Pinatubo, using the Hadley Centre/University of East Anglia surface temperature record, maximises at 0.14 °C globally and 0.32 °C over land. These values are about a factor of 2 less than found when the AMV index is neglected in the model and quite a bit lower than the canonical 0.5 °C cooling usually attributed to Pinatubo. This result is driven by the high amplitude, low frequency component of the AMV index, demonstrating that reduced impact of volcanic cooling upon consideration of the AMV index is driven by variations in North Atlantic SST that occur over time periods much longer than those commonly associated with major volcanic eruptions. The satellite record of atmospheric temperature from 1978 to present and other century-long surface temperature records are also consistent with the suggestion that volcanic cooling may have been over estimated by about a factor of 2 due to prior neglect of ocean circulation. Our study suggests a recalibration may be needed for the proper use of Mt. Pinatubo as a proxy for geoengineering of climate. Finally, we highlight possible shortcomings in simulations of volcanic cooling by general circulation models, which are also being used to assess the impact of geoengineering of climate via stratospheric sulfate injection. Final Revised Paperhttp://www.atmos-chem-phys.net/13/3997/2013/acp-13-3997-2013.pdf (PDF, 9366 KB) Supplementhttp://www.atmos-chem-phys.net/13/3997/2013/acp-13-3997-2013-supplement.pdf (828 KB) Discussion Paperhttp://www.atmos-chem-phys-discuss.net/12/23829/2012/acpd-12-23829-2012.html (ACPD) Citation: Canty, T., Mascioli, N. R., Smarte, M. D., and Salawitch, R. J.: An empirical model of global climate – Part 1: A critical evaluation of volcanic cooling, Atmos. Chem. Phys., 13, 3997-4031, doi:10.5194/acp-13-3997-2013, 2013. Bibtexhttp://www.atmos-chem-phys.net/13/3997/2013/acp-13-3997-2013.bib EndNotehttp://www.atmos-chem-phys.net/13/3997/2013/acp-13-3997-2013.ris Reference Manager http://www.atmos-chem-phys.net/13/3997/2013/acp-13-3997-2013.ris XMLhttp://www.atmos-chem-phys.net/13/3997/2013/acp-13-3997-2013.xml -- You received this message because you are subscribed to the Google Groups geoengineering group. To unsubscribe from this group and stop receiving emails from it, send an email to geoengineering+unsubscr...@googlegroups.com. To post to this group, send email to geoengineering@googlegroups.com. Visit this group at http://groups.google.com/group/geoengineering?hl=en. For more options, visit
Re: [geo] A critical evaluation of volcanic cooling
In my opinion, as I explained in comments on the submitted paper, http://www.atmos-chem-phys-discuss.net/12/23829/2012/acpd-12-23829-2012-discussion.html , this paper is fundamentally wrong. They double count the impact of volcanic eruptions on climate. In the final paper they even claim that Douglass and Knox were correct, with no reference to my paper or that from Tom Wigley and colleagues pointing out the errors. I recommend that you just ignore it and don't take the time to wade through it. It does not prove that the impact of volcanic eruptions is much smaller than previously thought nor that climate sensitivity is much smaller than commonly accepted. Robock, Alan, 2005: Comment on Climate forcing by the volcanic eruption of Mount Pinatubo by David H. Douglass and Robert S. Knox. /Geophys. Res. Lett./, *32*, L20711, doi:10.1029/2005GL023287. http://climate.envsci.rutgers.edu/pdf/DouglassKnoxComment2005GL023287.pdf Wigley, T. M. I., C. M. Ammann, B. D. Santer, and K. E. Taylor (2005a), Comment on ''Climate forcing by the volcanic eruption of Mount Pinatubo'' by David H. Douglass and Robert S. Knox, Geophys. Res. Lett., 32, L20709, doi:10.1029/2005GL023312. Alan Robock Alan Robock, Professor II Editor, Reviews of Geophysics Director, Meteorology Undergraduate Program Associate Director, Center for Environmental Prediction Department of Environmental Sciences Phone: +1-848-932-5751 Rutgers University Fax: +1-732-932-8644 14 College Farm Road E-mail: rob...@envsci.rutgers.edu New Brunswick, NJ 08901-8551 USA http://envsci.rutgers.edu/~robock http://twitter.com/AlanRobock On 4/24/2013 5:20 PM, Rau, Greg wrote: Atmos. Chem. Phys., 13, 3997-4031, 2013 www.atmos-chem-phys.net/13/3997/2013/ doi:10.5194/acp-13-3997-2013 © Author(s) 2013. This work is distributed under the Creative Commons Attribution 3.0 License. An empirical model of global climate -- Part 1: A critical evaluation of volcanic cooling T. Canty^1 , N. R. Mascioli^1,* , M. D. Smarte^2,** , and R. J. Salawitch^1,2,3 ^1 Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD, USA ^2 Department of Chemistry and Biochemistry, University of Maryland, College Park, MD, USA ^3 Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA ^* now at: Department of Earth and Environmental Sciences, Columbia University, New York, NY, USA ^** now at: Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA Abstract. Observed reductions in Earth's surface temperature following explosive volcanic eruptions have been used as a proxy for geoengineering of climate by the artificial enhancement of stratospheric sulfate. Earth cools following major eruptions due to an increase in the reflection of sunlight caused by a dramatic enhancement of the stratospheric sulfate aerosol burden. Significant global cooling has been observed following the four major eruptions since 1900: Santa María, Mount Agung, El Chichón and Mt. Pinatubo, leading IPCC (2007) to state major volcanic eruptions can, thus, cause a drop in global mean surface temperature of about half a degree Celsius that can last for months and even years. We use a multiple linear regression model applied to the global surface temperature anomaly to suggest that exchange of heat between the atmosphere and ocean, driven by variations in the strength of the Atlantic Meridional Overturning Circulation (AMOC), has been a factor in the decline of global temperature following these eruptions. The veracity of this suggestion depends on whether sea surface temperature (SST) in the North Atlantic, sometimes called the Atlantic Multidecadal Oscillation, but here referred to as Atlantic Multidecadal Variability (AMV), truly represents a proxy for the strength of the AMOC. Also, precise quantification of global cooling due to volcanoes depends on how the AMV index is detrended. If the AMV index is detrended using anthropogenic radiative forcing of climate, we find that surface cooling attributed to Mt. Pinatubo, using the Hadley Centre/University of East Anglia surface temperature record, maximises at 0.14 °C globally and 0.32 °C over land. These values are about a factor of 2 less than found when the AMV index is neglected in the model and quite a bit lower than the canonical 0.5 °C cooling usually attributed to Pinatubo. This result is driven by the high amplitude, low frequency component of the AMV index, demonstrating that reduced impact of volcanic cooling upon consideration of the AMV index is driven by variations in North Atlantic SST that occur over time periods much longer than those commonly associated with major volcanic eruptions. The satellite record of atmospheric temperature from 1978 to present and other
