The Carbon Cycle Questions I hope to address: ● What©s so special about Carbon anyway? ● Why do we care about the carbon cycle? ● Where does the Earth keep all it©s carbon? ● What factors determine atmospheric carbon dioxide concentrations? ● Where does the carbon dioxide we emit end up? ● What can we do to remove our excess carbon dioxide from the air? What©s so special about Carbon anyway? ● carbon has a unique chemistry that makes it disproportionately abundant in living organisms relative to it©s abundance on Earth. ● softest to hardest compounds on earth (graphiteÐi.e. pencil lead-- to diamond) are made of carbon Carbon is abundant in living organisms disproportionately to it©s abundance on earth... ● Carbon only makes up 0.094 % of Earth©s crust, and only 0.038 % of the atmosphere ● Humans are 18% composed of Carbon. Carbon forms Polymers ● A polymer is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. The term is derived from the Greek words: polys meaning many, and meros meaning parts[1] Hypothetical silicon-based life Silicon? ● Silicon makes up 28% of the Earth©s crust! (As opposed to carbon which is only 0.094%). ● Of meteorites and space dust, 84 carbon compounds but only 8 silicon, and 4 of those Why not silicon? ● Silanes (Si-H2) compounds are highly reactive with water. Why not silicon? ● Silanes (Si-H2) compounds are highly reactive with water. ● Carbon can form double and triple bonds, which silicon can©t as easily do. ● Combustion of C-H2 compounds produces carbon dioxide and water (both gases). Combustion of Si-H2 compounds produces SiO2, which is a solid! You©d have to breathe out bricks to use silicon. ● Silicon might be more important on extremely hot planets Why do we care about the carbon cycle? The other molecules are less likely to absorb infrared heat. ● Nitrogen 78.084% ● Oxygen 20.946% ● (oxygen and ozone absorb UV, visible and a little bit of IR) ● Argon 0.934% ● Carbon dioxide 0.038% ● (absorbs IR) ● Water vapor 1% ● (absorbs IR) ● Other 0.002% What Factors control carbon dioxide in our atmosphere right now? The Annual Cycle of Photosynthesis and Respiration from Mauna Loa Observatory ● Notice how the biologically driven annual cycle is a about a factor 10 greater than the anthropogenic increase over 1 year ● Known as the Keeling curve 17 18 Carbon Exchange With Plants · Photosynthesis: carbon dioxide + water + light => carbohydrate + oxygen CO2 + H2O + light => CH2O + O2 · Respiration: – ~half of the carbohydrates used to produce energy for metabolism O2 + CH2O => energy + H2O + CO2 – ~half used to form new plant tissue (biomass), so growing plants are net C sinks · Decomposition – Respiration by bacteria that consumes organic matter · Total exchange of CO2 ~1000 times faster than geologic exchanges 20 Oceanic Carbon ● Oceans store about 50 times more CO2 than the atmosphere and 19 times more than terrestrial biosphere CO2 CO2 ⇔ + - CO2 + H2O H + HCO3 21 Oceanic CO2 Pressure ● Difference between water pCO2 and atmospheric pCO2 ● Negative values (blue) mean the ocean takes up CO2 22 Oceanic Biological Pump ● Phytoplankton absorb CO2 ● Zooplankton consume phytoplanton – source of oceanic food web ● Respiration returns most of CO2 to the ocean ● Some organic matter sinks to ocean bed and provides a net (essentially permanent) uptake of CO2 into the ocean 23 Ocean Uptake Timescale ● Pre-industrial: – 98.1% CO2 in oceans – 1.9% in atmosphere ● For 100 molecules CO2 emitted today – 6 dissolve in 1 year – 29 in 10 years – 59 in 60 years – 84 in 360 years ● Currently 42% of CO2 emitted since 1800 has dissolved in the ocean ● At the time when atmospheric CO2 has doubled – 80-85% in oceans – 15-20% in the atmosphere The problem is the rate of emission of CO 2 27 Human Perturbation to the Carbon Cycle Human Perturbations to the Global Carbon Budget CO2 sources Flux (Gt C/yr) Fossil fuel combustion and cement production 5.5 ± 0.5 Tropical deforestation 1.6 ± 1.0 Total anthropogenic emissions 7.1 ± 1.1 CO2sinks Storage in the atmosphere 3.3 ± 0.2 Uptake by the ocean 2.0 ± 0.8 Northern hemisphere forest regrowth 0.5 ± 0.5 Other terrestrial sinks (CO2 fertilization, nitrogen fertilization, climatic effects) 1.3 ± 1.5 Source: Climate Change 1995, published by the IPCC While we understand the C-cycle in principle, the budget is not yet well quantified 29 Increasing emissions from the developing world · Over the next few decades, 90 percent of the world's population growth will take place in the developing countries, some of which are undergoing rapid economic development · Per capita energy use in the developing countries, which is currently only 1/10 to 1/20 of the US level, will also increase · If current trends continue, the developing countries will account for more than half of total global carbon dioxide emissions by 2035 · China, which is currently the second largest source, is expected to displace the US as the largest emitter by 2015 Kyoto Accord ± a quick review · The Kyoto Accord calls for the 38 industrialized countries by 2012 to reduce their combined annual gas emissions to 5.2 percent below levels measured in 1990. · It set a different negotiated target for each country (e.g., USA, 93% of baseline year ± 1.348.2 MtC What can we do to reduce the rate of CO2 increase in the atmosphere? ● Don©t put it in the atmosphere to begin with! ● Pump it into the ground or the deep ocean ● Grow Trees ● Sequester it with carbon dioxide absorbing minerals. Carbon footprint calculator ● http://www.carbonfootprint.com/USA/calculator.html ● Other ecological Footprint calculators ● http://www.ecobusinesslinks.com/ecological_footprint_calculator.htm Pump it into the ground? Some sinks: Pump it into the Deep ocean? Pump it into the deep ocean Store it in minerals? Geological time-scale carbon cycle Olivine could absorb CO2 · The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. It is one of the most common minerals on Earth, and has also been identified on the Moon, Mars, and comet Wild 2. Serpentinite reactions Reaction 1 Mg-Olivine + Water + Carbon dioxide → Serpentine + Magnesite + Silica Reaction 2 Fe-Olivine + Water + Carbonic acid → Serpentine + Magnetite + Magnesite + Silica Reaction 3 Serpentine + carbon dioxide → Magnesite + silica + water Store it in Trees? ● Trees are the main storage of terrestrial carbon ● First step is to reduce current forest clearance rates ● Do existing trees grow faster in a CO2-rich environment? ● What about new plantations? 50 Carbon and Land Use 1 Pg = 1 Peta gram = 1015 g = a thousand million million grams 51 Using Forests to Sequester Carbon · Total fossil fuel reserves can't be mopped up by trees – look back at the Reservoir Table · What happens to biomass growth rate with increased atmospheric CO2? – In experiments: Faster growth of forest pine trees for a few years, then return to normal since trees need other nutrients, such as nitrogen – Other experiments show unabated increased growth rates – Drought or other stress increases CO2 emissions ● Open issue, but trees unlikely to be a reliable CO2 remover 52 New Plantations · A conservative estimate for the amount of CO2 sequested by a 100 hectare Blue gum (Euc.globulus) plantation grown in Australia for 20 years can be worked out as follows: ● Growth rate of plantation – 20 cubic metres Stemwood/hectare/year ● Total stem wood volume at age 20 – 40,000 cubic metres ● One cubic metre of wood equals 0.32 tonnes of Carbon – Total wood volume=12,800 tonnes of Carbon ● Soil and non-stem Carbon accumulates at rates of about 2.5 tonnes/hectare/year – total soil and non-stem Carbon accumulated at age 20 = 5,000 tonnes of Carbon ● Total Carbon (wood, non stem and soil) at age 20 ± 17,800 tonnes of Carbon ● One tonne of Carbon = 3.67 tonnes CO2 – 100ha plantation would `capture' 65,000 tonnes of CO2 over the 20 year period, or an average of 3,270 tonnes CO2/year Question: What fraction of the world's land area would you need to cover in such trees in order to mop up 10 Pg CO2 emission from fossil fuels per year? A hectare (symbol ha) is a unit of area, equal to 10,000 square metres "Surface Area: Land area, about 148,300,000 sq km, or about 30% of total surface area; water area, about 361,800,000 sq km, or about 70% of total surface area." 53 The Carbon Budget 54 Carbon Exchanges Between Reservoirs ● Geologic carbon exchanges on time scale of millions of years ● Biological/physical carbon exchanges on the time scale of days to ~1000 years 55.