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 GHG responsible for the anthropogenic influence on the heat balance is CO2. The atmospheric concentration of CO2 has increased from 280 to 379 ppm (about 35 %) since the pre-industrial era in the nineteenth century (IPCC, Fourth Assessment Report). The main cause is the use of fossil fuels, but changing land use, including forest clearance, has also been a significant factor. Concentrations of the GHGs CH4 and N2O, which are very much linked to agricultural production, have increased by approximately 150 % and 18 %, respectively (IPCC, 2007). The lifetime of the gases in the atmosphere needs to be taken into account – the longer they remain in the atmosphere the greater the overall effect. The global warming potential (GWP) for various gases has been defined as the warming effect over a given time of a given weight of a specific substance relative to the same weight of CO2. The purpose of this measure is to be able to compare and integrate the effects of individual substances on the global climate. Typical atmospheric lifetimes for different substances differ greatly, e.g. for CH4 and N2O, approximately 12 and 120 years, respectively. So the time perspective clearly plays a decisive role. The lifetime chosen is typically 100 years. The effect of the various GHGs can then be converted into the equivalent quantity of CO2, i.e. the quantity of CO2 producing the same effect with regard to absorbing solar radiation. According to the IPCC and their Second Assessment Report, which UNFCCC has decided to use as reference, the global warming potentials 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 than CO₂. 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 (IPCC, 1996).

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 six main sectors. The greenhouse gases include CO₂, CH₄, N₂O, HFCs, PFCs and SF₆. The chart below shows the estimated total greenhouse gas emissions in CO₂-equivalents from 1990 to 2009. The emissions are not corrected for electricity trade or temperature variations. CO₂ is the most important greenhouse gas, followed by N₂O and CH₄ in relative importance. The contribution to national totals from HFCs, PFCs and SF₆ is approximately 1 %. Stationary combustion plants, transport and agriculture represent the largest sources as shown in the pie below. The net CO₂ emission by land use, forestry and soil (Land Use, Land Use Change and Forestry (LULUCF)) is in the region of 2 % of the total emission in CO₂-equivalents in 2009. The national total greenhouse gas emission in CO₂-equivalents without LULUCF has decreased by approximately 10.03 % from 1990 to 2009 and decreased by 15.9 % with LULUCF.

(Click the chart to view the background data)

Illustrations: Greenhouse gas emissions in CO₂-equivalents distributed on main sectors and for the time-series.

Read more about the greenhouse gasses:

• CO₂, Carbon dioxide
• CH₄, Methane
• N₂O, Nitrous oxide
• HFCs, PFCs and SF₆