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Greenhouse gases

 

About greenhouse gases and climate change

The greenhouse gases reported under the Climate Convention are:

  • Carbon dioxide (CO2)
  • Methane (CH4)
  • Nitrous Oxide (N2O)
  • Hydrofluorocarbons (HFCs)
  • Perfluorocarbons (PFCs)
  • Sulphur hexafluoride (SF6)

The main greenhouse gas responsible for the anthropogenic influence on the heat balance is CO2. The atmospheric concentration of CO2 has increased from 280 to 370 ppm (about 30%) since the pre-industrial era in the nineteenth century. The main cause is the use of fossil fuels, but changing land use, including forest clearance, has also been a significant factor. The concentrations of the greenhouse gases CH4 and N2O, which are highly linked to agricultural production, have increased by 150% and 16%, respectively. Changes in the concentrations of greenhouse gases are not simply related to these effects on the heat balance, however. The various gases absorb radiation at different wavelengths and with different efficiency. Moreover, the concentrations of some gases are so high that the radiation at some wavelengths is already nearly fully absorbed. An increasing concentration will therefore have a limited effect. This must be considered when assessing the effects of changes in the concentrations of various gases. Further, the lifetime of the gases in the atmosphere must be taken into account – the longer they remain in the atmosphere, the greater their overall effects. The global warming potential of various gases has been defined as the warming effect of a given weight of a specific substance relative to CO2. The purpose of this is to be able to compare and integrate the effects of individual substances on the global climate. The typical lifetimes are 100, 10 and 300 years for CO2, CH4 and N2O, respectively, and the time perspective clearly plays a decisive role. The lifetime chosen is typically 100 years. Then the effect of the various greenhouse gases can be converted into the equivalent quantity of CO2, i.e. the quantity of CO2 giving the same effect in absorbing solar radiation. According to the IPCC Second Assessment Reportthe most recent global warming potential values for a 100-year time horizon are:

  • CO2: 1
  • Methane (CH4): 21
  • Nitrous oxide (N2O): 310

Based on weight and a 100-year period, methane is thus a 21 times more powerful greenhouse gas than CO2 and N2O is 310 times more powerful. Some of the other greenhouse gases (hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride) have considerably higher global warming potential values. For example, sulphur hexafluoride has a global warming potential of 23,900.

The Climate Convention and the Kyoto Protocol

At the United Nations Conference on Environment and Development in Rio de Janeiro in June 1992, more than 150 countries signed the UN Framework Convention on Climate Change (the Climate Convention). On 21 December 1993 the Climate Convention was ratified by enough countries, including Denmark, for it to enter into force on 21 March 1994. One of the provisions was to stabilise the greenhouse gas emissions from the industrialised nations by the end of 2000. At the first conference under the UN Climate Convention in March 1995 it was decided that the stabilisation goal was inadequate. At the third conference in December 1997 in Kyoto, Japan, a legally binding agreement was reached, committing the industrialised countries to reduce the six greenhouse gases by 5.2% in the period 2008-2012 compared to the 1990 level. However for the F-gases the nations can freely choose between 1990 and 1995 as the base year. On May 16, 2002, the Danish Parliament voted for Danish ratification of the Kyoto Protocol. Denmark is, thus, under a legal commitment to meet the requirements of the Kyoto Protocol. The European Union must reduce emissions of greenhouse gases by 8%. However, within the EU, the member states have made a political agreement – the Burden Sharing Agreement – on the contributions by each state to the overall EU reduction level of 8%.

Under the Burden Sharing Agreement Denmark must reduce emissions by an average of 21% in the period 2008-2012 compared to the 1990 emission level.

In accordance with the Kyoto Protocol Denmark’s base year emissions include the emissions of CO2, CH4 and N2O in 1990 in CO2-equivalents and the emissions of HFCs, PFCs and SF6 in 1995 in CO2-equvivalents. Furthermore, the removals by sinks are included in the net emissions. Removals by sinks only include sequestration due to afforestation since 1990. When reporting to the Climate Convention the net CO2 removals by forests existing in 1990 are included in the calculation also.

The role of the European Union

Since the European Union (EU) is also a party to the UNFCCC and the Kyoto Protocol, and has to submit similar data sets and reports for the collective 15 EU member states as national Parties have, the EU imposes some additional guidelines to EU member states through the EU Greenhouse Gas Monitoring Mechanism to guarantee that the EU meets its reporting commitments.

Danish greenhouse gas emissions

The greenhouse gas emissions are estimated according to the IPCC guidelines and are aggregated into seven main sectors. The green-house gases include CO2, CH4, N2O, HFCs, PFCs and SF6. The figure shows the estimated total greenhouse gas emissions in CO2 equiva-lents from 1990 to 2004. The emissions are not corrected for electricity trade or temperature variations. CO2 is the most important green-house gas, followed by N2O and CH4 in relative importance. The con-tribution to national totals from HFCs, PFCs and SF6 is approximately 1%. Stationary combustion plants, transport and agriculture represent the largest sources. The net CO2 removal by forestry and soil (Land Use Change and Forestry (LUCF)) is in the region of 3% of the total emission in CO2 equivalents in 2004. The national total greenhouse gas emission in CO2 equivalents without LUCF has decreased by 1.5% from 1990 to 2004 and by 5.5% with LUCF.

Greenhouse gasses graph

Greenhouse gas emissions in CO2 equivalents distributed on main sectors for 2004 and Time-series for 1990 to 2004.

 

View backgrounddata for the graph

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Henrik Bruun

01.11.2007


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