|Characterisation Method Name:|
|The earth's atmosphere absorbs part of the energy emitted as infrared radiation from earth towards space, and is thereby heated. This natural greenhouse effect leading to a warming of the atmosphere has with certainty been increased over the past few centuries by human activities leading to accumulation of such compounds as CO2, N2O, CH4 and|
halocarbons in the atmosphere. The most import human contribution to the global warming impact is attributed to the combustion of fossil fuels such as coal, oil and natural gas.
The consequences of the man-made global warming may include increased global average temperatures and sudden regional climatic
The world-wide network of climate researchers and atmospheric chemists, the IPCC (Intergovernmental Panel on Climate Change), is following the latest development in our knowledge of global warming and issuing regular status reports. These status reports comprise the basis of the EDIP method's assessment tool for global warming.
Global warming is an impact affecting the environment on a global scale.
1 Determine which substances contribute to global warming
For a substance to be regarded as contributing to global warming, it must be a gas at normal atmospheric temperatures and:
• be able to absorb infrared radiation and be stable in the atmosphere with a residence time of years to centuries,
• be of fossil origin and converted to CO, on degradation in the atmosphere.
The EDIP method's criteria for which substances contribute to global warming generally follow the IPCC's recommendation of excluding indirect contributions to the greenhouse effect, i.e. contributions attributable to a gas affecting the atmospheric lives of other greenhouse gases already present. The indirect effects are difficult to model, and the IPCC is therefore refraining for the time being from quantifying indirect contributions with the exception of contributions from the gas methane (Albritton et al., 1995a). The EDIP method, however, goes further than the IPCC's recommendation in including the contribution from organic compounds which is due to their inevitable degradation to CO, in the atmosphere.
For every emission of CO, it is important to check whether it is a nett addition of CO, to the atmosphere or simply a manipulation of part of the natural biogeochemical carbon cycle. If the source of carbon is fossil (coal, oil, natural gas), conversion to CO, will mean a nett addition, If, however, there is a question of combustion or breakdown of material which does not derive from fossil carbon sources, but for example from biomass, there will normally be no nett addition because the material in question was generated recently by fixing of COz from the atmosphere, and it would in any event inevitably be broken down to 002 again (see Hauschild & Wenzel, 1997d, for a more detailed discussion).
The list of substances considered to contribute to global warming is short and it can be regarded as exhaustive. It is thus not necessary in practice to check whether a substance fulfils the criteria in order to
decide whether it is to be regarded as contributing to global warming.
The IPCC presents global warming potentials (GWPs), which for each individual greenhouse gas express the potential contribution to global warming from a given quantity of the gas relative to the contribution from a corresponding quantity of 002. Calculation of the GWP values is based on model simulations of the gases' expected behaviour in the atmosphere over a large number of years.
The present version of the EDIP method employs the GWPs presented by the IPCC in their 1994 status report (Albritton et al., 1995a) for calculation of the global warming potential.
The IPCC does not include indirect contributions from gases other than methane. The EDIP method nevertheless offers the option of including that part of the indirect contribution from volatile organic compounds (VOCs) and carbon monoxide (CO) attributable to their predictable conversion to CO2. This applies only if the gases originate from fossil resources.
The choice of time scale T plays a large
role in the magnitude of the equivalency factor. For those gases with atmospheric lives significantly shorter than that of the reference gas CO2 the equivalency factor decreases with an increase in T. The opposite is the case for those gases with significantly longer lives than C02. In
accordance with general LCA practice, the EDIP method recommends using a time scale of 100 years.