How greenhouse gases affect the climate
The Earth’s atmosphere contains various gases that absorb the heat radiated from the planet’s surface. Since they also allow most solar radiation to pass through, they are referred to as greenhouse gases. This is because greenhouses also allow solar radiation to pass through while retaining thermal radiation.
Natural greenhouse gas emissions, or GHG emissions, occur, for example, through volcanic eruptions and forest fires. They are what made life on our planet possible in the first place. Without this natural greenhouse effect, the Earth would still be frozen.
However, due to human activities, their concentration in the atmosphere has increased significantly since the 19th century. Industrialization in particular marked a turning point. The increased use of fossil fuels such as coal, oil, and gas released large quantities of greenhouse gases. The resulting anthropogenic greenhouse effect has caused the average temperature on Earth to rise continuously over recent decades, with consequences for the climate that are, in some cases, dramatic.
Different greenhouse gases
The most commonly emitted greenhouse gas is carbon dioxide (CO2). It is produced primarily through the combustion of coal, oil, and gas and contributes particularly strongly to global warming. In addition to CO2, however, there are other greenhouse gases with an even stronger climate impact, which are released, for example, through agricultural processes such as the use of fertilizers and pesticides, as well as through industrial processes.
In December 1997, the Kyoto Protocol identified the following climate-damaging greenhouse gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and the so-called fluorinated greenhouse gases, or F-gases, which include hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6). Since 2015, nitrogen trifluoride (NF3) has also been included.
According to the Emissions Database for Global Atmospheric Research (EDGAR), around 53.2 gigatonnes of greenhouse gases were emitted worldwide in 2024, excluding GHG emissions and removals from sources such as land use, land-use change, and forestry. The majority of emissions, 74.5 percent, came from fossil carbon dioxide — that is, from the combustion of fossil energy sources such as coal, oil, and gas. This was followed by methane at 17.9 percent, nitrous oxide at 4.8 percent, and F-gases at 2.8 percent.
In Germany, according to the German Environment Agency, around 88.2 percent of greenhouse gases emitted in 2024 were attributable to carbon dioxide, 6.8 percent to methane, 3.6 percent to nitrous oxide, and around 1.4 percent to fluorinated gases.
CO2 equivalents enable comparability
To measure the impact of different greenhouse gases on the climate, the unit CO2 equivalents, also referred to as CO2e or CO2eq, has become established. By converting different types of emissions into the equivalent amount of carbon dioxide, these impacts can be made comparable. CO2, with a Global Warming Potential, or GWP, of 1, serves as the reference value.
Global Warming Potential is calculated over a specific period of time, such as 20, 100, or 500 years. In international reporting, the 100-year time horizon, GWP100, is mandatory. According to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC), the GWP100 of methane, for example, is 27. This means that one tonne of methane and one tonne of CO2 together would correspond to 28 tonnes of CO2e.
Deutsche Bahn accounts for all greenhouse gases considered material under the GHG Protocol in its greenhouse gas accounting. In Scope 1, 2, as well as 3.3, 3.4 and 3.11, these are generally CO2, CH4 and N2O. In Scope 3.1 and 3.2, the spend-based approach applied by DB takes into account the greenhouse gases CO2, CH4, N2O, HFCs, PFCs, SF6 and NF3. The respective Global Warming Potential values are based on the IPCC’s Sixth Assessment Report, using the 100-year GWP.
The basis for DB’s greenhouse gas accounting consists of final energy consumption data collected and aggregated across the Group, data on other sources of emissions and performance data, as well as the emission factors used consistently throughout the DB Group. Sources for the factors and methods used include the Institute for Energy and Environmental Research Heidelberg (ifeu), the EcoTransIT World accounting tool, the German Environment Agency (UBA), XIO Sustainability Analytics, the GHG Protocol, and DB’s own calculations.
The transport sector is responsible for around 20 percent of greenhouse gas emissions in Germany as of 2023. Road transport, including passenger cars and trucks, accounts for a significant share of this. In recent years, there has been little progress in reducing these emissions. In fact, emissions have even increased in some areas, such as aviation and shipping.
Overall, the transport sector is considered particularly difficult to decarbonize, as dependence on fossil fuels remains high. However, a positive trend can be observed in rail transport, where CO2e emissions have been continuously reduced since 1990.
Deutsche Bahn’s long-distance rail services are the most climate-friendly means of mass transport in Germany. This advantage is primarily due to the use of green electricity for DB traction power. In 2025, the share of green electricity had already reached 71.5 percent.
Deutsche Bahn will become climate-neutral by 2040 and has committed to achieving net-zero greenhouse gas emissions across the entire value chain by 2040. This target has been backed by an implementation plan and validated by the renowned and independent Science Based Targets initiative (SBTi).
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