Global Carbon Cycle

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Carbon is exchanged between the active pools due to various processes – photosynthesis and respiration between the land and the atmosphere, and diffusion between the ocean and the atmosphere.

Carbon Pools

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Carbon is stored on our planet in the following major pools: • as organic molecules in living and dead organisms found in the

biosphere; • as the gas carbon dioxide in the atmosphere; • as organic matter in soils; • in the lithosphere as fossil fuels and sedimentary rock deposits such as

limestone, dolomite and chalk; • in the oceans as dissolved atmospheric carbon dioxide and as calcium

carbonate shells in marine organisms.

• Carbon (as CO2) is accumulated… – Photosynthesis uses sunlight to make

carbohydrate from CO2.

• Carbon (as CO2) is released…– Respiration - carbon is oxidized for energy.– Combustion - carbon is burned– Weathering - rain (slightly acidic) weathers

calcium carbonate rocks

Carbon Cycle Has Been In Balance for Millions of Years

• But in the last century CO2 levels have been creeping up.

• Why?

Carbon Cycle Has Been In Balance for Millions of Years

• But in the last century CO2 levels have been creeping up.

• Why? - (burning of fossil fuels).

Greenhouse gassesin the atmosphereact like the glass ina greenhouseor car.

The Greenhouse EffectThink of the inside of a car in the summer…

UV radiation from the sun passes through the glass,warms up the seats, and gets trapped

Heat (infrared) doesn’tpass back out through glass easily

The Greenhouse Effect is a Good Thing

Because Mars has almost nogreenhouse gasses, heat fromthe sun goes back into outer space. Average temperature = -10 °F

Venus has too much of a good thing…

High CO2 levels on Venustrap too much heat. Temperature is nearly 800 °F.Even hotter than planet Mercury (350 °F),which is closer to the sun.

Atmospheric CO2 Concentration-1

4/12Accurate and direct measurements of the concentration of CO2 in the atmosphere began in 1957 at the South Pole and in 1958 at Mauna Loa, Hawaii.

Atmospheric CO2 Concentration-2

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In 1958, the concentration of CO2 was about 315 ppmv, and the growth rate was about 0.6 ppmv/yr. This growth rate has generally been increasing since then; it averaged 0.83 ppmv/yr in the 1960s, 1.28 ppmv/yr during the 1970s, and 1.53 ppmv/yr during the 1980s. The concentration in 2006 was over 380 ppmv.

The annual cycle in the Mauna Loa record is due to the seasonality of vegetation. In early spring, the concentration of CO2 is at its maximum, and as the plants green-up, the concentration drops, reaching a minimum value towards the end of the summer, and when leaves fall, it starts to build up again. This swing in the amplitude is most pronounced in the records from the northern high latitudes, where it can be as large as 15 ppmv.

Major Greenhouse Gasses

• Water vapor Does much to keep planet warm. We have no control over water vapor.

• CO2 is the most significant greenhouse gas. Levels increasing because of fossil fuel burning. We should be concerned about this one.

Other Greenhouse Gasses

• Methane - from wetlands, ruminants and commercial production. 20-30 times more potent than CO2. Levels going up slowly.

• Nitrogen oxides (NOx or NxO) - formed during combustion from N2 that’s in air. 200-300 times more potent than CO2.

• Chloroflurocarbons (CFC’s) - Foam insulation, refrigeration gas, used to be an aerosol propellant. Being phased out.

• Ozone - formed from lightning, electrical arcs, and a reaction of gas vapors and sunlight.