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Dictionary

Carbon Dixoide

Carbon dioxide is the result of many natural processes. All of these have a long-term balanced cycle in the biosphere. Humans are interrupting this natural balance.

Carbon is the basis of all life. Molecules which contain carbon as a basis, or have carbon in a chain, or polymers, are known as organic molecules.

Carbon is essential for life on the planet, and is circulated through the biosphere and lithosphere by the mechanisms of the carbon cycle. Carbon enters the life cycle through photosynthesis, where plants absorb CO2, unite it with water, under the energy of sunlight, to produce cellulose, which is (C6H12O5)n. This large molecule is then converted to sugar (glucose C6H12O6), and consequently amino acids, proteins, and all the substances which comprise organisms.

The main pathway of carbon is the atmosphere. There is a long-term balance of CO2 in the atmosphere of around 300 parts per million (0.3%). You are right to think this is not very much. For every carbon dioxide molecule floating around in the atmosphere, on average there are 70 oxygen molecules, and 240 nitrogen molecules!

GISS images
Images courtesy of NASA’s Goddard Institute for Space Studies (GISS)

So, if carbon is in such low quantities, and so essential to life, it may be tempting to think that problems would arise if there were too little carbon, not too much?

The problem lies with fossil fuels. Although there is a rough balance between plant transpiration (converting atmospheric carbon to solid cellulose) and respiration (the return of carbon to the atmosphere as CO2, when we breathe out, or burn something), there is also a 'big picture' part of the carbon cycle. Carbon is 'lost' from the biosphere, as peat is pushed underground, or sealife dies and drifts into sea sediment. And carbon is brought back into the atmosphere through the disintegration of carbonate rocks, which becomes magma, which is fired out of volcanoes.

These lithosphere (underground) sinks and sources of carbon should also remain in a rough long-term equilibrium. Fossil fuels (coal, oil, gas) are mid-stages of carbon in sinks (dead organic matter being squeezed by the Earth's weight as it sinks deeper into the crust). This carbon is many millions of years old, and is supposed to stay out of the atmosphere for a long time still.

Solar and Earth radiation spectra
Solar and Earth radiation spectra: the Sun's incident radiation is short-wavelength, and the Earth's is long-wavelength

However, since the Industrial Revolution began to burn coal at ever-increasing rates, and motor vehicles have been burning millions of tonnes of oil per year, this carbon has been brought back into the biosphere far too early, and has caused an sharp increase in the amount of CO2 in the atmosphere. In fact, instead of 0.3%, there is now 0.4% CO2 concentration in the troposphere, the first 15 km of the atmosphere. That's how busy we have been generating energy from fossil fuels for two hundred years!

This excess of carbon acts like a blanket around the Earth. The incident solar radiation has a shorter wavelength than thermal radiation. This means that most of the sunlight can pass through the atmosphere, to be absorbed by the Earth's surface, which warms. The Earth then re-radiates this energy with a longer wavelength, in the infrared portion of the electromagnetic spectrum. CO2, methane and water in the atmosphere can absorb this longer wavelength, trapping the energy in the atmosphere. Instead of re-radiating the right proportion of the Sun's radiation energy each day, the Earth retains more and more of it, gradually heating the land, sea and atmosphere.

Carbon dioxide is the major greenhouse gas that is produced by human activities. That is why carbon is the no. 1 culprit in climate change, and the only solution is to stop using fossil fuels. The percent reductions discussed by the Paris Conference, December 2015, the Kyoto Protocol, and the UNFCCC, are political targets. There is no 'safe level' of excess carbon emissions, at which we can be sure we do not cause an irreversible change to the biosphere.

We are a large mammal, enjoying a temporary niche in a dynamic system. Any alteration to the baseline conditions will not be to our benefit.

Carbon dioxide (CO2) is a greenhouse gas, and therefore a major cause of anthropogenic global warming.

CO2 Sources

Fossil fuels: 29.5% power generation, 19.2% road vehicles, 12.9% domestic and commercial, 20.6% industry

Range

Global

Effects

Principal cause of the enhanced greenhouse effect, which is responsible for the observed global warming and climate change. Carbon dioxide is one of the at least eight gases released by human activity which alter the atmospheric characteristics, principally infrared radiation and re-radiation, resulting in a retention of re-radiated heat by the atmosphere.

Counter-measures

Proposed transition of economies from inefficient, fossil-fuel based to more efficient and less fossil-dependent economies. In particular, industry and power generation are subject to restrictions, and the Kyoto Protocol provides for the financial instrument of carbon credits (IET market), which puts a price on carbon emissions, according to the Polluter Pays Principle. Much research and government-backed incentives promote the use of alternatives to fossil fuels in all areas of CO2 generation, in particular renewable energy schemes and subsidised markets.

Outlook

Global CO2 emissions have continued to rise, despite increasing evidence of the veracity of global warming. The actions of the USA in undermining the Kyoto Protocol has led to its ineffectiveness in curbing emerging economies from adopting dirty technologies, rather than committing to the clean technology mechanism proposed by Kyoto.

There are indications that political awareness may yet bring about the widespread adoption of existing and new technologies, and that very dirty practices, such as shale oil, will be prevented from undoing any progress made. The USA is leading the obstruction lobby, as before.

Resources

The Carbon Dioxide Information Analysis Center (CDIAC)

The Carbon Dioxide Information Analysis Center (CDIAC), located at the U.S. Department of Energy's (DOE) Oak Ridge National Laboratory (ORNL), is the primary climate change data and information analysis center for the US DOE.

Carbon dioxide sinks remove carbon from the surface of the Earth. Before humans began to burn fossil fuel, there was a long-term balance between carbon output from volcanoes and sinks in the sea and anaerobic processes on land.

SourceStorageImmissionSinkNet carbon balance
Atmospheric pool720; 1.6%
Biosphere2,000; 4.4% 10.390
Fossil fuels4,130; 9.1% 0
Oceans38,400; 84.7%8.3 -1.6-2.4

The figures in the table above refer to 1015 mols of CO2 (carbon dioxide).

Carbon in the Earth's Carbon Cycle has both organic and inorganic forms. Most inorganic carbon is carbon dioxide (CO2), carbonate (CO32-) and hydrogen carbonate (HCO3-, aka bicarbonate). Organic carbon is carbon in living and dead organisms, fossil fuels, and other organic deposits dispersed in rock, water and the atmosphere.

Respiration of living organisms liberates solar energy stored in glucose during photosynthesis.

Carbon is passing continuously between the inorganic and organic forms. Inorganic carbon is in an oxidised form, which is reduced through photosynthesis to organic form. Hence CO2 is reduced to glucose (C6H12O6). As a more complex chain of carbon atoms, the glucose contains much more energy than CO2. It is this energy storage which fuels living organisms. Through respiration, carbon is oxidised through a series of steps to return to inorganic CO2 at its lowest energy level.

Carbon in the crust is of biological origin, and has a residence time of 2.7 x 105 years. This carbon is mainly the deposits of living organisms which used calcium carbonate (CaCO3) in their shells, and formed sedimentary rock, limestone or related rocks, also formed through metamorphism. Carbonate rock is essentially a permanent reservoir of carbon, however a small amount of carbon is released back into the atmosphere through volcanoes.

In anerobic conditions, such as in swamps, there is insufficient oxygen available to oxidise the carbon in detritus (leaves and dead organisms), so carbon is lost to the environment in what is known as a carbon sink. It is this carbon which is compressed and heated underground to form the fossil fuels: coal, gas, and oil. Thanks to the anaerobic land and ocean carbonate carbon sinks, the Earth has retained a balance between oxygen and carbon dioxide.

Carbon in the crust is of biological origin, and has a residence time of 2.7 x 105 years. This carbon is mainly provided by the deposits of living organisms which used calcium carbonate (CaCO3) in their shells, and forms sedimentary carbonate rock, such as limestone, or subsequent rocks through metamorphism. Carbonate rock is essentially a permanent reservoir of carbon, however a small amount of carbon is released back into the atmosphere through volcanoes.

In anaerobic conditions, such as in swamps, there is insufficient oxygen available to oxidise the carbon in detritus (leaves and dead organisms), so carbon is removed from the surface environment in what is known as a carbon sink. It is this carbon which is compressed and heated underground to form the fossil fuels: coal, gas, and oil. Thanks to the anaerobic land and ocean carbon sinks, the Earth has retained a balance between oxygen and carbon dioxide through the mechanism of life.

Human activities are currently the greatest source of imbalance to the finely-tuned carbon cycle

Carbon as CO2 in the atmosphere has a short residence time. On average, a CO2 molecule released during respiration or decomposition will circulate in the air for just 3.2 years, before being returned to the life cycle through photosynthesis. The atmosphere mixes due to wind systems on about the same timescale. This means that local variations in CO2 concentrations can be created. There are also natural variations in the influx and outfluxes of carbon, due to variations in climate, weather, and volcanic activity. Human activities are currently the major cause of carbon imbalance in the planet's carbon cycle, releasing over 50 Gt of carbon dioxide annually from fossil fuel burning.

Estimates of carbon reservoirs

/Gt (billion tonnes carbon)

  • Atmosphere: 800
  • Biomass: 550
  • Soil: 2300
  • Reactive sediments: 6000
  • Ocean surface: 1000
  • Deep ocean: 37,000
  • Fossil fuels: 10,000
Estimates of natural carbon flows

/Gt (billion tonnes carbon) annual

  • Plant respiration: 60
  • Photosynthesis: 120
  • Microbial decomposition and respiration: 60
  • Air-sea gas exchange: 90 released / 92 uptake
Estimates of carbon accumulation/sinks

/Gt (billion tonnes carbon) annual

  • Anthropogenic (primarily burning fossil fuel) contributions to atmosphere: 9
  • Total natural atmosphere exchange: 5
    • Net terrestrial uptake: 3
    • Net ocean uptake: 2

The atmosphere has a net 4Gt per year accumulation of carbon due to the burning of fossil fuel and other human activities.

The CO₂ footprint, also known as the CO₂ balance, is a measure of the total amount of carbon dioxide emissions (measured in CO₂-equivalent) that is caused, directly and indirectly, by activity or by the life stages of a product.

As there is no internationally recognized definition, some calculations also include all greenhouse gases or additional factors.

Carbon dioxide emissions (measured in CO₂) and greenhouse gas emissions (measured in CO₂ equivalents, CO₂-eq) are often expressed in tonnes per year, or in vehicles per gram per kilometer.

The CO₂ footprint has gained in importance in recent years, as it could be a helpful tool to determine the environmental impacts of products, services and other events in the everyday life of every human being. Only with this information can the climate impacts be effectively minimized, which in turn is necessary to achieve targeted climatic conditions - for example limiting global warming to 2 ° C.

Energy Footprint

The average US household has an annual carbon footprint of 50 tons CO2e per year, which is five times the global average 10 tons CO2e per household per year.

Coal is the dirtiest fuel in common usage for electricity, and for each Megajoule of thermal energy produced emits c. 91 g(CO2e)/MJth of black coal (anthracite), or c. 94 g(CO2e)/MJth for brown coal (lignite). This equates to c. 900 g(CO2e)/kW⋅he of generated electricity for black coal. Brown coal emits c. 900 g(CO2e)/kW⋅he of generated electricity.

Standards

ISO 14067: Accounting for the carbon footprint of products.

In the United Kingdom, a standardization of the carbon footprinting method of products with the British standard 'PAS 2050: 2008', prepared by BSI (British Standards Institute), was completed in 2008.

Examples

Beef: ca. 13 kg CO₂-eq per kilo (varies depending on transport, storage and type of preparation)

Potatoes: ca. 600g CO₂-eq per kilo

Washing powder: 600-850g CO₂-eq per load.

Orange juice: 880-1440g CO₂-eq per litre.

Lumination: 60W incandescent bulb = 34kg CO₂-eq per 1000 hours of use; 11W LCD = 6,5kg CO₂-eq per 1000 hours of use.