1Announcements• Exam on Thursday (th h t d ’ t i l)(through today’s material)• Exam review (based on review questions posted a week ago) tonight at 5pm.Anthropogenic CO2: where does all the carbon go?(a summary of carbon cycle)Gl b l Ch n L t S S l sk 2N2010I. Past: Arrhenius, Revelle, and Keeling: does anthropogenic CO2accumulate in the atmosphere?II Present: where does the carbon go?Global Change Lecture, S. Saleska, 2-Nov-2010II. Present: where does the carbon go?III. Future: What will be the fate of carbon sinks/sources in the future?2I. Arrhenius, Revelle, and Keeling:Does anthrpogenic CO2 accumulate in the atmosphere?“On the Influence ofOn the Influence of Carbonic Acid in the Air upon the Temperature of the Ground,”by Svante Arrhenius(1896)Arrhenius’ 1896 prediction of temperature change induced by doubled CO2(“carbonic acid=2.0”):Included:Mean annual temperature changeLatitude bands- More warming at high latitudes than low- more warming in winter than during the summer-doubled CO2 global average = 5+ CHigh latitudes:Tropics (current IPCC estimate: 1.5 – 4.5C)High latitudes:≈ 6.0p≈ 53Arrhenius’ 1896 prediction of temperature change induced by doubled CO2(“carbonic acid=2.0”):Included:Latitude bands- More warming at high latitudes than low- more warming in winter than during the summer- doubled CO2 global average = 5+ C(current IPCC estimate: 1.5 – 4.5C)Naïve calculation• Assumption: Added carbon will partition itself between the ocean and atmosphere in the samebetween the ocean and atmosphere in the same proportions that it exists there now: Atm/Ocean = 600 Pg/38,000 Pg = 1/63(i.e. 1/63 = 1.5% of added CO2 will stay in the atm)So Arrhenius didn’t think this warming would ever happen, and neither did most scientists for another 60 years. Until…4"Human beings are now carrying out a large scale geophysical experiment of ageophysical experiment of a kind that could not have happened in the past nor be reproduced in the future." • Revelle & Suess (1957)Roger Revelle, seen here studying seawater chemistry, ca. 1936, and as a leading adminstrator as well as scientist, ca. 1958.(Source: Weart: http://www.aip.org/history/climate/ )Chemistry ofDissolution of CO2 in SeawaterCarbonate chemistry in the oceans:(Covered in ocean biogeochemistry lecture #1, 10/19) yCO2+ H2O  H2CO3 (CO2 to carbonic acid)H2CO3 H++ HCO3-(carbonic acid to bicarbonate)HCO3- H++ CO3-2(bicarbonate to carbonate)----------------------------------------------------Net: CO2+ H2O + CO3-2 2HCO3-the ability to dissolve CO2 depends on the relative concentrations of the carbonate ions (CO3-2& HCO3-) which are controlled by ocean alkalinity (details in previous lectures on Ocean carbon)The net result is that the factor by which the oceans can take up CO2 is reduced by a factor of ~10. This factor is called the “Revelle factor”5Charles David Keeling. Keeling’s test of Revelle’s hypothesis(anthropogenic CO2 was not going into the ocean, but was staying in the atmosphere)A rising level of CO2 in the atmosphere was first demonstratedatmosphere was first demonstrated in 1960 in Antarctica, visible after only two years of measurements. (Keeling, 1960)This work definitively confirmed Revelle’s hypothesisAbove: 1961Right: in 1990sPart II. Present: where does all the carbon go?The question we started with inThe question we started with in Terrestrial Biogeochemistry lecture #1 (9/28)6Uptake by= land and oceansQuestions about carbon uptakePart IIWhere does all the carbon go?Part II.Where does all the carbon go?1. How do we tell how much is going into the land, and how much is going into the ocean?2. What causes the high interannualgvariability in atm. CO2? (the wiggles?)Part III.What about the future?71. How much CO2is going into the land, and how much is going into the ocean?Methods:Atmospheric“Inverse modeling”Methods: Atmospheric Inverse modeling(a) combine global atmospheric CO2 data with global model of atmospheric transport– Identify where CO2 is added and removed to/from atmosphereTans et al 1990simple example–Tans et al. 1990 -simple example(b) Multi-tracer inversionsexample: combine CO2 and O2 (Ralph Keeling et al)What is “inverse modeling”?• Imagine a model that, given a pattern of dik fCO2 th th’sources and sinks of CO2 on the earth’s surface, predicts a resultant pattern of concentrations in the atmosphere• Run this model backward (i.e. “invert” the model) to get the pattern of sources andmodel) to get the pattern of sources and sinks from the atmospheric concentrations8O2 nHypothetical examples: #1: balanced carbon cycle, no net sources and sinksAtmospheric COconcentrationlattitudeequatorSouthpoleNorth poleHypothetical examples: #2: fossil fuel emissions (current pattern): no net sources/sinksO2 nAtmospheric COconcentrationlattitudeequatorSouthpoleNorth poleSource/sinkFossil fuel9Global CO2observation networkObserved (red) and modeled (blue) CO2Obs. CO2Blue lines:various oceanuptake scenariosused as model input(blue) CO2 profiles with latitude from Tans et al. 1990Obs. CO290°S90°N• Ocean uncertainties cannot explain observed gradient• Given a NH source, we require a NH sink (non-ocean) to balance• Conclude: NH terrestrial biosphere a significant sink• specific estimate out of date, but conclusions stand test of time10Partitioning terrestrial and oceanic carbon exchange:a multiple tracer approachA) Biological COexchange is intimately Inverse model example (b): CO2 & O2A) Biological CO2exchange is intimately coupled with O2exchange: photosynthesis produces O2, respiration consumes itB) Ocean-atmosphere CO2exchange is physical Recall: Carbon is the currency of lifePhotosynthesis/Resp.: H2O + CO2 CH2O + O2)p2gpydissolution, so oceanic CO2uptake does not influenceatmospheric O2C) Thus, the relationship between the CO2 and O2content of the atmosphere provides a fingerprintof biological and oceanic CO2exchangesBlue = Atm. O2/N2Red = CO2Alaska:Australia:111) We know how much fossilfuels we’re burning (and that combustion requires O2)Starting point in 1990(1990-2000)Potential end-point in 2000 (no sinks)1) We know how much fossilfuels we’re burning (and that combustion requires O2)3) We know the O2:CO2ratio associated with land-atmosphere COexchange 2) But we observeless CO2increaseand O2decrease thenwe should based on knownfossil fuel emissionsatmosphere