Greenhouse effect, 1950-2002
The enhanced greenhouse effect caused jointly by the global greenhouse gases increased further in 2002, and is now more than 2.5 W/m2. Since 1980, the greenhouse effect has increased less quickly.
Greenhouse effect continues to increase
The enhanced greenhouse effect caused by global greenhouse gases is currently more than 2.5+/-0.25 Watts per m2. The greenhouse effect is intensifying because of the emission of greenhouse gases from human activities. The greenhouse effect is currently increasing by approximately 3 W/m2 per century, as opposed to 5 W/m2 per century in the years around 1980. This deceleration is primarily the result of the termination of CFC production under the Montreal Protocol (UNEP, 1987-2000).
The enhancement of the greenhouse effect, also known as radiation forcing caused by greenhouse gases, means that more energy reaches the earth's surface than is lost to space. The result is an increase in the temperature on the earth's surface. The cause of the greenhouse effect is the increasing concentration of greenhouse gases. This in turn is the result of emissions of greenhouse gases from human activities.
The contribution of greenhouse gases to the enhanced greenhouse effect
- Carbon dioxide (CO2) now accounts for 61% of the enhanced greenhouse effect,
- with methane (CH4) accounting for 19%,
- nitrous oxide (N2O) for 6%,
- CFCs and HCFCs together for 13%
- and PFCs, HFCs, and SF6 for 0.7%.
The influence of ozone
The discussion above relates to the "global" greenhouse gases only. These are the greenhouse gases with a long life that, as a result, get well mixed into the atmosphere. Ozone is also an important greenhouse gas of which the concentrations are affected by human activity. Unlike the global greenhouse gases, ozone is not emitted directly by human activities. Ozone is formed in the atmosphere and it is broken down partly in the atmosphere and partly on the earth's surface. Ozone concentrations are affected by human emissions of various substances that form ozone or break it down, such as nitrogen oxides, volatile organic compounds, and hydrocarbons containing chlorine and bromine.
As a result of human activities, the ozone concentration in the lower atmosphere (the troposphere) has increased in recent centuries. This increase enhances the greenhouse effect caused by the global greenhouse gases by 0.35+/-0.2 W/m2. Tropospheric ozone is therefore the third most important greenhouse gas (after CO2 and CH4) in terms of its contribution to the enhanced greenhouse effect. In the higher atmosphere (stratosphere), the concentration of ozone actually fell after 1980. This is the result of the increase in concentrations of chlorine and bromine compounds, which decompose in the stratosphere and break down ozone there. As a result, the greenhouse effect generated by ozone has fallen by 0.15+/-0.1 W/m2.
The net effect of changes in ozone concentrations is therefore an enhancement of the greenhouse effect by 0.35 - 0.15 = 0.2 W/m2.
Kyoto Protocol
The Kyoto Protocol (UNFCCC, 1997) and the Climate Treaty of the UN (UNFCCC, 1992) are agreements made with a view to stabilising concentrations of greenhouse gases. The idea is that this will reduce the human impact on the climate. In order to stabilise greenhouse gas concentrations in time, emissions of greenhouse gases caused by humans must be reduced by more than half compared to 1990. The Kyoto Protocol covers the gases CO2, CH4, N2O, HFCs, PFCs and SF6.
CFCs and HCFCs are not covered by the Climate Treaty since they are regulated under the Montreal Protocol (UNEP, 1987-2000) on the protection of the ozone layer in the stratosphere.
How is the greenhouse effect calculated?
The greenhouse effect (radiation forcing caused by greenhouse gases) is calculated using the increase in the concentration of greenhouse gases compared to the preindustrial period, defined roughly as 1750. Furthermore, the greenhouse effect also depends on the radiation of heat through the atmosphere. That depends on the greenhouse gas in question, and is also affected, in the case of some greenhouse gases, by the concentrations of the other greenhouse gases. The total contribution of the various gases is the greenhouse effect, expressed in W/m2. This is the amount of extra energy falling per second onto a square metre of the earth's surface.
The figure only shows the effect of the direct greenhouse gases; the greenhouse effect of tropospheric ozone (caused by CO, NOx, VOC, CH4 and some other gases) as well as the cooling effect of aerosols (caused, among others, by SO2) are not included. These indirect influences partly cancel each other out.
References
- IPCC (2001). The Scientific Basis, Houghton et al. (eds.), Intergovernmental Panel on Climate Change (IPCC). Cambridge University Press, Cambridge, U.K. 881 pp, 2001.
- UNEP (1987 - 2000). The Montreal Protocol on substances that deplete the ozone layer (with amendments).
- UNFCCC (1992). United Nations Framework Convention on Climate Change. Rio de Janeiro, 1992.
- UNFCCC (1997). Kyoto Protocol to the United Nations Framework Convention on Climate Change. Kyoto, 11 December 1997. Link to PDF file. Link to HTML version.
Relevant sections and indicators in the Environmental Data Compendium
- Environmental pressure, theme of Climate change: introduction and Climate change: policy
- Depletion of the ozone layer: policy
- See the 'Global air quality' guide for a reference to the concentrations of greenhouse gases and for data about the greenhouse effect and the consequences for the climate.
- See the 'Environmental pressure, theme of Climate change (greenhouse effect)' guide for the emissions of substances that affect the climate.
- Concentration of greenhouse gases, 1980-2002
- Concentration of ozone-depleting substances, 1980-2002
Relevant information outside of the Environmental Data Compendium
- Information about the Climate Treaty and the Kyoto protocol can be found on the website of the United Nations Framework Convention on Climate Change (UNFCCC).
- Information about Dutch climate policy can be found on the website of the Ministry of Housing, Spatial Planning and the Environment.
- More information about the effects of climate change on the weather can be found on the website of the Royal Netherlands Meteorological Institute.
- More information about climate change and concentrations of greenhouse gases can be found on the websites of the IPCC (Intergovernmental Panel on Climate Change) and ETC/ACC (European Topic Center on Air and Climate Change).
- Information about current and future developments for the Kyoto Protocol can be found in Environmental Balance 2003 and National Environmental Outlook 2000-2030, both of which are RIVM publications.
