The Carbon Cycle Where does the CO 2 go? PowerPoint 97 To download: ShiftLeftClick Please respect copyright on this material

Key Points F Natural cycling of carbon through living things into plants/soil and coal and oil/limestone F Very different residence times in different parts of system F Rates of deforestation and burning fossil fuel small but accumulate for decades F Biological feed backs poorly known

Increasing Carbon Dioxide F Why the wiggles? F Why the trend?

Annual Wiggles in CO 2 F CO 2 used by plants in photosynthesis – making leaves in summer time – decaying back to CO 2 in winter South Nort h summer Pol e Pole Pole

CO 2 and Vegetation

CO 2 with latitude and year F Japan Climatic Data Center

Key Points F Natural cycling of carbon through living things into plants/soil and coal and oil/limestone F Very different residence times in different parts of system F Rates of deforestation and burning fossil fuel small but accumulate for decades F Biological feed backs poorly known

Background Facts F kg C = 1 Gt C = 1 billion tons carbon F Only 1/2 CO 2 from fossil fuel and deforestation still in atmosphere F CO 2 essential for photosynthesis – carbon dioxide + water + sunlight -> sugar F CO 2 dissolves in water – primarily as carbonate HCO 3 - – solubility less when warm, can of soda

The Pre-Industrial Carbon Cycle F Reservoirs in Gt C F Fluxes in GtC/y F Horel & Geissler Figure 6.3

Atmosphere - Vegetation Exchange annual cycle F Uptake by plants, approx 100 Gt/y Controlled by photosynthesis F Respiration as CO2, approx 100 Gt /y Some tissue maintenance, remainder decay of plant matter F Net storage in tree-trunks and soil carbon (decades) +/- ? GtC/y, residence time ~ 40 y F Atmosphere residence time 8 years

The Pre-Industrial Carbon Cycle F Flux Biota-Soil F Leaves, branches, roots become part of soil F Horel & Geissler Figure 6.3

Atmosphere - Surface Ocean Exchange annual cycle F Uptake by ocean, 92 GtC/y controlled by atmospheric concentration F Loss to atmosphere, 90 GtC/y controlled by ocean concentration and temperature F Upper ocean concentration rises, tending to balance, residence time 10 y

The Pre-Industrial Carbon Cycle F CO2 Dissolves In Water F Net flux down as atmospheric concentration increases

Deep Ocean Time Scales 1000 y F Gain, 39 Gt C/y, by sinking from surface in high latitudes and from fecal pellets F Loss, 37 Gt C/y, by upwelling into surface layer F Net gain, 2 Gt C /y, controlled by concentration difference, surface - deep F Total reservoir 40,000 Gt C (large) F Volcanic, weathering inputs small and nearly fixed

The Conveyor Belt

The Pre-Industrial Carbon Cycle F Reservoirs in Gt C Up welling Down welling Fecal Pellets

Geologic Time Scales 100’s of millions of years Geologic Time Scales 100’s of millions of years F balanced partition between atmosphere, biota, ocean F carbon removed 0.2 Gt /y (small) by deposit of limestone sediments, controlled by concentration CO2 in ocean F carbon inserted by volcanoes, weathering of exposed limestone, controlled by plate tectonics F total carbon 60 million Gt (huge)

The Pre-Industrial Carbon Cycle F Reservoirs in Gt C F Fluxes in GtC/y F Horel & Geissler Figure 6.3

Geologic Sources of CO 2 Geologic Sources of CO 2 F Volcanic Emissions F Weathering

CO 2 and Human Activities

Key Points F Natural cycling of carbon through living things into plants/soil and coal and oil/limestone F Very different residence times in different parts of system F Rates of deforestation and burning fossil fuel small but accumulate for decades F Biological feed backs poorly known

The Present Carbon Cycle F Atmosphere +3 GtC /y F Soil, deep ocean +2 GtC /y -2 per year

Atmosphere-Vegetation- Surface Ocean 10’s of years F Vegetation-atmosphere, ocean- atmosphere near balance F Atmospheric perturbation driven by fossil fuel and deforestation, 6 GtC /y F As atmospheric CO2 rises, partially compensating uptake by vegetation and surface ocean, 2.5 GtC /y F Deep ocean concentration fixed

Forcing Gt C /y Response ppm 1900

Key Points F Natural cycling of carbon through living things into plants/soil and coal and oil/limestone F Very different residence times in different parts of system F Rates of deforestation and burning fossil fuel small but accumulate for decades F Biological feed backs poorly known

Ecosystem Communities

Vegetation Responds to Enhanced CO2 F Other things being equal –plants grow faster –use water more efficiently F Measured net uptake of CO2 by mid- latitude forests F Indirect effects from climate change hard to model

Ice Age Variations F Due to solubility and vegetation changes?

Key Points F Natural cycling of carbon through living things into plants/soil and coal and oil/limestone F Very different residence times in different parts of system F Rates of deforestation and burning fossil fuel small but accumulate for decades F Biological feed backs poorly known

Sources of Information F Horel and Geisler Chapter 6, 5 F Japan Climate Data Center F Climate Change 1994