Patchy Cooling in a Warming World. Half Earth, title

Transcription

1 Patchy Cooling in a Warming World Half Earth, title

2 What have we learned? What Have We Learned About Climate Change from a Century of Research? Robert J. Charlson Department of Atmospheric Sciences, University of Washington A short history Conclusions Summary and analysis; Philosophical perspective Connections to biogeochemical cycles

3 Early History Early History Studies of the Earth s Heat Balance 1. Fourier (1827): The atmosphere augments the Earth s temperature because:...light finds less resistance in penetrating the air, than in repassing into the air when converted into non-luminous heat. -AND- Heat dissipated at the surface of the Earth is compensated at each instant by that received by the sun. 2. Tyndall (1860s): Gases, including CO 2 and H 2 O, can emit and absorb infrared radiation.

4 Arrhenius pictures 3. Arrhenius (1896): Performed the first calculations of the sensitivity of the surface temperature of Earth to changes in CO 2 and H 2 O. Included the water vapor feedback. Connected the warming effects of increased CO 2 to the global carbon cycle. Based the radiative transfer calculation on spectra of the IR emission of the moon, from Samuel Langley. 21 bands.

5 Arrhenius article scan

6 Discoveries of the mid-to-late 19th century that inspired and made possible Arrhenius calculation of the greenhouse effect of CO 2 and H 2 O: 1. Demonstration of absorption and emission of infrared radiation by CO 2 and H 2 O gases (Tyndall and others) 2. Measurement of the sun s emission flux 3. Measurements of the moon s reflection and emission taken through the Earth s atmosphere Infrared absorption of the atmospheric content of CO 2 and H 2 O gas Albedo of the Earth (Langley; Abbot) 4. Theory of radiative balance of absorption and emission Kirchoff s Law Stefan-Boltzmann Law: ~T 4 5. Occurrence of ice ages on Earth Agassiz Discoveries 19th

7 The 1930s to the 1950s 1. Callendar (1938) CO 2 has increased by 10% Causes observable warming Much disbelief among scientists 2. Suess (1955) CO 2 has gone up and it is due to CO 2 from fossil fuels; based on 12 C/ 14 C ratio in pre-bomb tree rings 3. Plass (1956) First detailed study of CO 2 spectrum Concluded that increased CO 2 will heat the Earth 4. Revelle (1956) Oceans are a meager sink for CO 2 Need to measure CO 2 5. Keeling ( ) Established standardized measure of CO 2 Demonstrated secular increase Measurements continue today 1930s to

8 Variation in concentration of atmospheric carbon dioxide in the Southern Hemisphere (Keeling 1960). Keeling 1960 CO 2

9 1960s The 1960s 1. Keeling and others Much more data showing increase of CO 2 2. Junge and others Debate over the causes Much disbelief that cause might be anthropogenic 3. Kondratiev and Niilisk (1960), Kaplan (1960), Möller (1963) Radiative equilibrium models of warming by increased CO 2 4. Manabe and Weatherald (1967) First radiative/convective model 5. Rasool and Schneider (1969) Suggested the possibility that aerosol pollution could trigger an ice age 6. Crutzen (1969) Catalytic reduction of O 3 by NO in stratosphere (QJRMS, 1970)

10 1970s 1-5 The 1970s 1. Junge (1976) Separated direct and indirect effects of aerosols Compared CO 2 and aerosols 2. Mitchell, Bryson, others Attempted to connect aerosols to observed cooling 3. Bolin and Charlson (1976) Suggested that anthropogenic sulfates would cause lower T in industrial areas Failed to separately calculate forcing (W/m 2 ) by aerosols 4. Lovelock and Margulis (1974) Atmospheric Homeostasis by and for the Biosphere: the Gaia Hypothesis 5. Improvements in Computers

11 1970s, Bolin; Twomey The 1970s, cont. 6. Bolin and others (mid-1970s) Beginnings of large international research projects (SCOPE; GARP) 7. Twomey (1971) Sensivity of cloud albedo to droplet population

12 1980s, Ram; D&C The 1980s 1. Ramanathan et al. (1985) Recognition of greenhouse gases other than H 2 O and CO 2 (CH 4, N 2 O, CFCs ) 2. Dickinson and Cicerone, Nature (1986) Separation of forcings ( thermal trapping ), W/m 2 from responses (ΔT) allows the comparison of different forcing agents: 1985 F ΔF GAS amount (W/m 2 ) ( ) CO 2 CH 4 O 3 (trop) CFC11 CFC12 N 2 O 345 ppm 1.7 ppm ppb 0.22 ppb 0.38 ppb 304 ppb ~

13 1980s, Grassl The 1980s, cont. 3. Grassl (1988) Existence of a large negative forcing by anthropogenic aerosols (e.g., SO 4 ) Anthropogenic aerosol particle influence outside clouds on solar radiation, for particles without soot (thick line) and with 20% soot (thin line).

14 1980s, Lorius The 1980s, cont. 4. Lorius et al. (1987) Ice core records reveal very low CO 2 in ice ages Petit et al., Nature (1999)

15 Petit figure

16 1980s, Coakley; Charlson The 1980s, cont. 5. Coakley, Bernstein and Durkee, Science (1987) Observations of the influence of droplet size on cloud reflectance 6. Charlson, Lovelock, Andreae and Warren, Nature (1987) Hypothetical feedback involving marine phytoplankton, dimethylsulfide, cloud albedo

17 1990s, Charlson; Kiehl The 1990s 1. Charlson et al. (1991) = First global map of calculated forcing by SO 4 aerosol Negative forcing comparable in magnitude to that of CO 2, opposite in sign (-0.3 to -1 W/m 2, cf by man-made GHG) 2. Kiehl and Briegleb (1993) Forcings by CO 2 and by aerosols are not geographically uniform

18 Sci. American fig Results from Kiehl & Briegleb, as used in: Charlson and Wigley, Scientific American, 270 (1994) Average heat gain, July 1993 (watts per square meter)

19 The 1990s, cont. 3. Karl et al. (1995) Patterns of temperature change are not uniform T change similar to aerosol map

20 1990s, Keeling, Mauna Loa The 1990s, cont. 4. Keeling, R. (1996) CO 2 increase is linked to O 2 decrease

21 1990s, 5 & 6 The 1990s, cont. 5. Development of intergovernmental protocols: Intergovernmental Panel on Climate Change (IPCC, 1990, 1992, 1994, 1995) Framework Convention on Climate Change (FCCC) a. Rio de Janeiro (1992) b. Berlin (1995) c. Geneva (1996) d. Kyoto (1997): binding agreements to reduce CO 2 emission e. Buenos Aires (1998) 6. First attempts to measure actual climate forcings by aerosols (US, India, China) a. Tarfox b. Indoex c. ACE-ASIA 7. Centennial of Arrhenius paper, Stockholm, April 1996

22 2000s The 2000s 1. IPCC 2001, EOS satellites focused on climate 3. A-Train of 5 satellites flying in formation, climate focus: a. Aqua b. Calipso c. CloudSat d. Parasol e. Aura 4. FCCC Copenhagen, Dec, 2009

23 Conclusions Summary so far While still very uncertain, the magnitude of negative forcing by anthropogenic aerosols is sufficiently large to have balanced a substanital part of the global-mean greenhouse gas forcing. 2. Temperature change is not the only useful metric of imposed climate change. 3. The concept of climate forcing (W/m 2 ) provides a metric for imposed climate change in addition to and as an alternative to temperature change. 4. The magnitude of temperature changes to be expected in the future cannot be more certain than the forcings that are the cause of the expected warming. 5. In spite of the large uncertainties, it is inevitable that the net forcing will be increasingly positive in the future because CO 2 and other man-made GHGs accumulate in the air while aerosols do not.

24 Schwartz et al. (2007), Nature Reports: Climate Change, 1, Rosy

25 Too Serious! BUT! We are getting too serious

26 Wizard of Id

27 Scientists R Us

28 Dubridge quote 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. Dr. Lee Dubridge Science Advisor to President Nixon US News and World Report January, 1970

29 Caveat CAVEAT: Aerosol effects and greenhouse gas effects cannot simply cancel each other out. WHY? Because they occur at different places and times in the atmosphere.

30 Evolution part 1: 1-6 Evolution of Science/Policy Debate s: Arrhenius estimates 500 years would be needed for doubling of CO 2 ; sums up impact on humans: Our descendants might live under a milder sky and in less barren natural surroundings than is our lot at present : First reports of increased CO 2 from attempted chemical measurements; high uncertainty led to some debate over methodology s s: Developments in nuclear chemical methods. J. Willard Libby develops carbon dating based on 14 C; Hans Suess notes secular increase of 12 CO 2 in tree rings before bomb testing. Geochemists agree that CO 2 increase is real. Atmospheric scientists are skeptical s: The IGY and beginnings of monitoring of CO 2 by Keeling. Debate over whether humans could cause CO 2 to increase. (Note comments of B.J. Mason and C.E. Junge.) s: Debate over the global temperature increase from ca , and the cooling from ca Debate over possibility of a human-induced ice age in spite of CO 2 increase. 6. Beginnings of the environmental movement White House Conference on the Environment: Restoring the Quality of Our Environment. Through his worldwide industrial civilization, Man is unwittingly conducting a vast geophysical experiment. Within a few generations he is burning the fossil fuels that slowly accumulated in the Earth over the past 500 million years.

31 Evolution part 2: 7-11 Evolution of Science/Policy Debate, cont s: Beginnings of interest in climatic effects of aerosols. (Mitchell, Bryson, Junge ) s: Debate over relative importance of natural variability, other forcing agents. Use of forcing (W/m 2 ) as index of the extent of human influence. Note that ΔF of 6-7 W/m 2 is projected to occur by ca. 2100, and is about the same magnitude as the ΔF at the end of an ice age. (6-9 W/m 2 ) s: Recognition that T is increasing and beginnings of debate over whether humans are the cause. Beginnings of the IPCC. 2000s: Recognition that humans are a cause of T increase but debate over how much temperature increase is harmful s, cont.: In some circles, recognition that a few to several degrees of T increase would be harmful and debate over ways to adapt to it. Q.E.D: The debate shifts to the cutting edge of scientific research, whenever progress is made.