Half Earth no title I Aerosol effects

Half Earth, no title

I. Aerosol effects on climate: A short history Half Earth, title slide Robert J. Charlson Departments of Atmospheric Sciences and Chemistry University of Washington, Seattle Or… An idiosyncratic view of how aerosol-climate research arrived at where it is today… Photo credit: “The Blue Marble” http: //visibleearth. nasa. gov/view_rec. php? id=2429

1. The Climatic Role of Volcanism Plutarch (44 B. C. ) Re: cooling caused by Etna eruption Franklin (1784) Re: cool summer in Europe caused by Laki eruption Tambora Eruption (1815) Caused “year without a summer, ” 1816, as far away as New England Humphreys (~1912) Attempted quantification of cooling from volcanic aerosols Mitchell (1961) Volcanoes cause interannual temperature change Lamb (1970) Dust veil index Minnis et al. (1993) Satellite (ERBE) observation of cooling of -1 to -2 W/m 2 caused by Mt. Pinatubo, T~ -0. 5 C Robock (1995) Review 1. Role of Volcanism

Krakatoa, 1883 artist’s rendering Krakatoa

2. Atmospheric Haze Optics Tyndall (1861) Particles scatter visible light Ångström (1929) Defined atmospheric “turbidity” and its wavelength dependence Volz (1956) Popularized measurement of turbidity • Flowers et al. (1969) Network of turbidity observations showed horizontal scale of ca. 1000 km 2. Atmospheric Haze Optics

cai. blogware. com/_photos/Smog. jpg Smog

2. Atmospheric Haze Optics, cont. GMCC/CMDL (1976 – ), WMO-BSRN (early 1990 s – ) Nephelometric and radiometric monitoring data in rural /remote locations Charlson and Pilat (1969) Aerosols can either heat or cool the Earth depending on light absorbing property Lin et al (1973) First filter data on light absorption by urban aerosols (Samples from NYC 1967) 2. continued

3. Visibility Koschmieder (1924) Theory of visual range Bergeron (1929) Observation in Sweden of long-range transport of visible hazes from the south Middleton (1952) Book: Vision Through the Atmosphere Rossano and Charlson (1965 – ca. 1972) Project: “Influence of aerosol characteristics on visibility” Duntley (1948 – ca. 1966) The Visibility Laboratory; Scripps Institution of Oceanography: Theory and observation of visibility in atmosphere and oceans 3. Visibility

4. Wartime and ”Cold War ” Aerosol Research and High Level of Secrecy (1914 to mid 1960 s) Waldram (1945) Measurement of optical transmission of atmosphere; both absorption and scattering (illuminated white target on ground with balloon-borne radiometer, at night) Beuttell and Brewer (1949) Integrating nephelometer development during WWII Green and Lane (1964) Described basic aerosol science needed by militaries (respirable chemical and biological agents; smoke screens for visibility degradation etc. , from the U. K. Chemical Defence Experimental Establishment, Porton Down) 4. Wartime & Cold War

Nephelometer

4. Wartime and ”Cold War" Aerosol Research, cont. Anonymous (1940 s – 1950 s) Use of GE condensation nucleus counter for tracking snorkeling submarines; declassified ca. 1964 Fuchs (1955) Soviet textbook on aerosol mechanics; classified version available to US military and US Public Health Service Fuchs (1964) Declassified book published in the West HASL (1940 s until ca. 1965) High altitude sampling of radioactivity; discoveries of slow interhemispheric transport Ahlquist and Charlson (1967) UW obtains US patent on the high-sensitivity version of the integrating nephelometer 4. Wartime, continued

Snorkel

5. Astronomical Approach; Solar Irradiance Langley (1884) Method of estimating solar constant from flux at different air masses; yields both atmospheric optical depth and solar constant Abbot (1911) Aerosol correction factor for determination of “solar constant” Danjon (1928) Albedo of Earth via observation of the moon when illuminated by “Earthshine” Hodge et al. (1968 – ca. 1972) Project ASTRA, using observations with astronomical telescopes by NASA of star brightness to infer atmospheric aerosol optical depth NASA Pioneer 5 (1959) Beginnings of satellite monitoring of solar flux; detailed solar flux record 5. Astro Approach

6. Tropospheric “Background Aerosol” Effects Bryson (1967, 1974) Cooling due to anthropogenic changes in dust, e. g. , from deserts Mc. Cormick and Ludwig (1967) Increase in turbidity might be the cause of global cooling since the 1940 s Cobb (1970, 1973) No change in electrical conductivity of air over North Pacific and Southern Hemisphere; decrease over North Atlantic due to aerosol pollution Mitchell (1970) Cooling from ca. 1940 s to 1960 s was an enigma and possibly part of a climatic “rhythm” Mitchell in SCEP (1971) Lengthy discussion of heating versus cooling by anthropogenic aerosols 6. Tropospheric

6. Trop. “Background Aerosol” Effects, cont. Rasool and Schneider (1971) “An increase by only a factor of 4 in global aerosol background concentration may be sufficient to reduce the surface temperature by as much as 3. 5° K”; suggested that this might “trigger an ice age” Kellogg (various) Anthropogenic perturbation of “background aerosol”; used GNP as proxy for aerosol in global dispersion model 6. Tropospheric, continued

6. Trop. “Background Aerosol” Effects, cont. Junge (1975) Suggested use of 2 - or 3 -D tropospheric source-transportremoval model; identified aerosol by region, not by chemical composition; defined background aerosol that fills “ 80% of the volume of the troposphere” Robock (1978) Estimated the effect of anthropogenic aerosols by scaling to anthropogenic increase of CO 2 Coakley et al. (1983) “Background aerosol” cools Earth surface by 2 – 3° K 6. Tropospheric, continued

7. Climatology; Indices of Climate Change Avicenna (11 th century) Hotness and coldness measured by expansion of a gas de Medici (1654) Alcohol thermometer Fahrenheit (1724) Temperature scale Celsius (1742) 100 degree temperature scale based on freezing point and boiling point of water Anon. (ca. 1850) Beginnings of instrumental T record; T as index of climate 7. Climatology

7. Climatology; Indices of Climate Change, cont. Keeling (1957, 1960) Beginning and first data for continuous monitoring of CO 2; change of CO 2 as index of climate change; definition of T 2 x Ramanathan (1980) Concentrations of numerous GHG as indices of climate change (CO 2, CH 4, N 2 O etc. ) Dickinson and Cicerone (1986) Magnitude of the imposed change in heat balance as index of climate change (W/m-2); emphasized that it was more certain than modeled temperature changes or forecasts Charlson, Lovelock, Andreae, and Warren (1987) CLAW hypothesis proposing a feedback of aerosol from marine dimethylsulfide on cloud albedo 7. Climatology, cont.

8. Cloud Physics Coulier (1875) and Aitken (1880) Particles are necessary formation of droplets in an expansion cloud chamber Arrhenius (1896) “Nebulosity ” is a key factor in global heat balance C. T. R. Wilson (1912) Expansion cloud chamber; detection of subatomic particles Köhler (1936 and earlier) Theory: Water soluble particles act as cloud condensation nuclei (CCN); equation describing equilibrium cloud droplet size as a function of supersaturation 8. Cloud Physics

8. Cloud Physics, cont. Junge (1975) Differenti ated between direct effect of aerosols on solar radiation and indirect effect of aerosol CCN on cloud albedo Twomey (1971, 1977) Theory of the effect of CCN on cloud albedo Charlson et al. (1987) Proposed that changes in emission of marine algal dimethylsulfide would influence cloud albedo 8. Cloud Physics, cont.

9. Aerosol Science and Atmospheric Chemistry World War I British physicochemist F. G. Donnan coined term “aerosol”, meaning particles suspended in a gaseous medium; analogous to “hydrosol” 1940 s until mid 1960 s Stratospheric sampling of radioactive bomb debris Junge (1962) Summarized measurements of aerosol properties and size distributions in book “Air Chemistry and Radioactivity” Bullrich (1964) Book describing aerosol effects on atmospheric radiative transfer; largely the 9. Aerosol Sci results of post WWII research on atmospheric optics/radiative & Atmos Chem

9. Aerosol Sci. and Atmospheric Chem. , cont. Whitby and Clark (1966) Electronic method for measuring “complete” size distribution based on ion mobility Whitby et al. (1972) and Husar et al. (1972) First measurements and dynamical explanation of bimodal size distribution of Los Angeles smog Charlson et al. and Waggoner et al. (1967 -1976) Summarized light scattering efficiency of tropospheric aerosols From Journal of the Air Pollution Control Association, 1969 9. Aerosol / Atmos, cont.

9. Aerosol Sci. and Atmospheric Chem. , cont. Covert et al. (1974) Measure ment of the increase in aerosol scattering caused by increased RH, utilizing a (then) modern version of the Beuttell & Brewer nephelometer. Waggoner et al. (1976) Sulfatelight scattering ratio; empirical observations from aircraft of scattering efficiency by sulfates: (5 m 2/g dry; 8. 5 m 2/g at average PBL RH) 9. Aerosol / Atmos, cont.

10. Chemically-Identified Anthropogenic Aerosol Date? Chemical mechanism; SO 2 as source of SO 4 = aerosol via gas-to-particle conversion Bolin and Charlson (1976) Loss of solar radiation and cooling in industrial regions due to anthropogenic sulfate aerosol; predicted temperature decrease in industrial regions; missed the connection to regional sulfur mass balance Charlson, Langner and Rodhe (1990, 1991) Radiative forcing of climate by anthropogenic sulfate, global mean ca. -0. 6 W/m 2 (hereafter “climate forcing”) Penner and Dickinson (1992) Forcing by smoke from biomass combustion 10. Chemically-identified

11. Modeling Arrhenius (1896) Simple equilibrium model of incoming solar radiation and outgoing longwave radiation; included “nebulosity” due to clouds as an influence on albedo Plass (1961) Equilibrium surface temperature as f (CO 2) Manabe and Wetherald (1967) 1 -D radiative convective model, no aerosols Rasool and Schneider (1971) 1 -D planetary radiation model with aerosols and fixed clouds Budyko (1969) Climatic effect of loss of solar radiation (Tellus) Manabe and Wetherald (1975) 3 -D radiativeconvective model with fixed clouds and no aerosol 11. Modeling

11. Modeling, cont. Isaksen and Rodhe (1980) 2 -D model of atmospheric sulphur, including sulfate aerosols Zimmerman (1987) 3 -D model of cycling of atmospheric tracers (MOGUNTIA) Langner and Rodhe (1991) 3 -D model of atmospheric sulfur, using MOGUNTIA Charlson, Langner and Rodhe (1990, 1991) Climate forcing by anthropogenic sulfate aerosols; utilized a 0 -D and then a 3 -D mass balance model of anthropogenic sulfur (MOGUNTIA) plus empirical scattering efficiency and angular scattering information Knutti and others (early 2000 s) Inverse calculation using a climate model and known/assumed sensitivity to yield aerosol climate forcing 11. Modeling, cont.

12. Sulphate aerosol and climate, Nature, Vol. 348, p. 22 (1990). R. J. Charlson Department of Atmospheric Sciences, University of Washington, Seattle J. Langner, H. Rodhe Department of Meteorology, Stockholm University, Sweden … A simple box-model calculation illustrates the expected magnitude of the mean column burden of anthropogenic sulphate, BSO 2– : 4 BSO 2– = 4 2– FSO 4 SO 2– 4 A ~ (3. 3 106 g s-1)(5 105 s) 2. 5 1014 m 2 ~ 6. 6 10 -3 g m-2) F 2 where – SO 4 is the average flux of this SO 42– through the atmosphere in the Northern Hemisphere (equivalent to about half of 70 Tg yr -1 of sulphur emitted as SO 2); SO 2– is the mean sulphate aerosol particle lifetime (about 4 6 days) and A is the area of the northern Hemisphere. We assume that all 2 anthropogenic SO 4 – originates and stays in the Northern Hemisphere. 12. Simple Calculation

12. Sulphate aerosol and climate, Nature, Vol. 348, p. 22 (1990), cont. An empirical optical scattering efficiency, (10 m 2 g-1, ref. 2), then yields an estimate of optical depth SO 2– , for solar wavelengths due to 4 2 anthropogenic SO 4 – : 2 SO 2– = BSO 4 ~ – 4 0. 066 Finally, an empirical backscatter fraction, (0. 15, ref. 3), and estimated cloud fraction, f (~0. 6), allow for estimation of the energy lost from the Earth’s surface, L (we disregard the effect of aerosols above cloudy areas): L ~ (1 - f ) SO 2– (2 SO 2–) ~ 4 4 0. 8% where the factor of two is the secant of solar zenith angle averaged over the sunlit hemisphere… 12. Simple Calculation

13. Aerosol Sensing from Satellites (Examples) Stowe, Durkee et al. (1978 – ) Advanced Very High Resolution Radiometer (AVHRR); aerosol optical depth (inverse method) Mc. Cormick et al. (1979 – ) Stratospheric Aerosol and Gas Experiment (SAGE); limb scanner; volcanic plumes Cess, Ramanathan et al. (1984 – ? ) Earth Radiation Budget Satellite (ERBS); ERBE on NOAA 9, 10; scanning multi-band radiometer (broadband) Mc. Cormick et al. (1994) Lidar In-Space Technology Experiment (LITE) aboard Shuttle Wielicki et al. (1997, 1999 – ) Clouds and the Earth’s Radiant Energy System (CERES); based on successful ERBE instrument French Space Agency (1996 -7, 2002 -3, – ) Polarization and Directionality of the Earth’s Reflectances (POLDER) Winker et al. (2006 – ) 13. Aersol Sensing from Satellites

14. International Collaborative Reviews That Included Aerosol Effects on Climate Matthews et al. (1971) Study of Critical Environmental Problems (SCEP) SMIC (1971) Inadvertent Climate Modification GARP (1975) The Physical Basis of Climate and Climate Modeling (GARP 16) SCOPE (1971 -1986…) Several books on biogeochemical cycles 14. International Collab.

15. Political Recognition of Climate Change and Aerosols Revelle et al. , in White House conference on the environment (1965) Anthropogenic CO 2 increase amounts to an unplanned and unpredictable “vast geophysical experiment” Dubridge (1970) “If we were clever enough to balance these two effects – the reflectivity of particulate matter and the concentration of carbon dioxide – the Earth's temperature might stay constant. ” (U. S. News and World Report, Jan. 1970) US NRC (1991) Discussed the possibility of adding aerosols to cancel out GHG effects J. Climatic Change (2006) Special issue on geoengineering with articles by Cicerone, Crutzen, and others; “Geoengineering” by adding aerosols to the stratosphere might be necessary IPCC (1990, 1992, 1995, 2001, 2007) Aerosols included as climate forcing agents first in 1992, introduced to IPCC by Rodhe and Watson 15. Political Recognition

15. Political Recognition of Climate Change and Aerosols, cont. Steven Schwartz (2007), personal communication 15. Political Recognition

II. Conclusions 1. Many areas of scientific endeavor have contributed to current knowledge of aerosol effects, from astronomy to geology and atmospheric chemistry. 2. Many of these areas are isolated from one another and interchange has been slow and dependent upon random efforts by individuals. 3. All of the necessary information to calculate global climate forcing by anthropogenic sulfates was available by ca. 1976, but the key to doing it appeared to be the emphasis of forcing as an index of climate change rather than temperature. II. Conclusions

II. Conclusions, cont. 4. Projecting to the future, the need for faster/more certain progress would seem to require interdisciplinary coordination as well as accurately posing the scientific questions re: what we do not yet understand cannot yet measure with sufficient accuracy. 5. International coordination is needed. 6. Example of a large uncertainty that presently impedes progress: Measurement of global albedo and sensitivity of albedo to perturbations from either climate change or aerosols. II. Conclusions