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Biologically CO₂ is very important because it is takes part in the photosynthesis and in respiration, which are essential processes for living species. The photosynthesis is a biochemical reaction that takes place in green plants when sunlight is used to transform CO₂ and water to glucose, oxygen and energy. The opposite reaction takes place during respiration of living species; oxygen and glucose is then transformed back to CO₂ and water.

Environmental impacts of CO₂ Emissions

Global CO2 emissions. Source: Wikipeda.

Increasing CO₂ emissions is mainly a result of combustion of fossil fuels like coal, oil and gas for energy production. There has been a large increase in global anthropogenic (human made) CO₂ emissions since the industrial revolution 250 years ago as shown in Figure 1.

The Greenhouse Effect

Radiation from the sun will be reflected by the surface of the earth as infrared radiation. The greenhouse effect is a natural process where some gases in the atmosphere reflect the infrared radiation back to the earth. Without this natural greenhouse effect, the global average temperature would have been -19 ^oC, and not +15 ^oC as it is today.

Scenarios for atmospheric CO2 concentration and global temperature increase. The different lines represent different models. Source: IPCC.

Water vapor is the most important gas leading to greenhouse effect, but because atmospheric water vapor concentration is hardly effected by human activity, this is referred to as natural greenhouse effect.

Gasses leading to greenhouse effect are called greenhouse gasses (GHG). If the atmospheric concentration of GHGs increases due to human activity the result will be man made greenhouse effect. The most important GHGs leading to manmade greenhouse effect are CO₂, ozone (O₃), N₂O, methane (CH₄) and CFCs (Cloro­fluor­carbones). The most important GHG leading to anthropogenic global warming is CO₂.

According to IPCC, there is no doubt that increasing anthropogenic CO₂ emissions are leading to global warming.

The consequences of too high global warming will be melting of glaciers, leading to reduced water and food resources. The sea level will rise, and there will be more extreme weather, more draughts, and more floods. As a consequence more than 200 million humans can become climate refugees. Ecosystems will be disrupted, and 15 to 40 percent of all species can be extinct.

Acidification of the Oceans

CO₂ can be dissolved in the oceans, and increasing atmospheric CO₂ concentration will increase the amount of dissolved CO₂. The result will be acidification of the oceans, which can lead to serious consequences for species living under water.

Strategies to cut emissions

A global warming of more than 2 ^oC increase in global average temperature will lead to serious consequences, and IPCC have therefore suggested that global GHG emissions should be reduced by 50 to 80 percent by 2050. This is a tremendous challenge, especially when energy demand and fossil fuel consumption increases rapidly in developing countries like China and India. Even if we are able to keep the increase in average global temperature below +2 ^oC, there will be dramatic climate changes, especially in artic areas.

Reduction of global CO₂ emissions requires a combination of several strategies; the energy consumption must be reduced through enhanced energy efficiency and the production of renewable energy must be increased. The potential of such measures are far too small to close the gap between global energy demand and renewable energy production, and the world will therefore be dependent on fossil fuel for decades.

Additional strategies are requires to obtain sufficient cut in global CO₂ emissions. Governments must establish economic incentives and regulatory framework to strengthen research and development of new low emission technologies.

Another alternative for reducing CO₂ emissions is to switch from fossil fuel energy production to nuclear energy. However, this is considered as a bad strategy due to the potential hazards related to nuclear energy production and nuclear waste. Another argument is that the potential for CO₂ emission reduction due to increased nuclear energy production is relatively small.

CO₂ Capture and Storage

A promising technology for reducing global CO₂ emissions is Carbon dioxide Capture and Storage (CCS), which has a large potential for reducing global CO₂ emissions on a relatively short time-scale. CCS includes CO₂ capture from CO₂ sources, transportation of CO₂ to a storage site, and safe underground storage of CO₂. CCS is applicable to large CO₂ point sources like fossil fuelled power plants and large industrial sources.

CO₂ capture refers to the process where CO₂ from a flue gas is separated from the other flue gas components.

Transportation of compressed CO₂ can be performed by pipelines or ship.

Aquifer storage and CO2 used for EOR

CO₂ storage can take place in suitable underground geological structures, for example depleted oil and gas reservoirs or saline formations; so-called aquifers, see Figure 3. Before CO₂ storage can be deployed on a global scale, methods and standards for CO₂ storage must be established to ensure safe storage without leakages.