Environmental news No. 80 2005 – Spatial differentiation in LCA impact assessment

Spatial differentiation in LCA impact assessment

2. Global Warming

Background information for this chapter can be found in:

Chapter 1 of "Environmental assessment of products. Volume 2: Scientific background" by Hauschild and Wenzel (1998a).
Chapter 4 of "Guideline in normalisation and weighting – choice of impact categories and selection of normalisation references" by Stranddorf et al., 2005.

2.1 Introduction

The environmental mechanisms underlying global warming, and the climate change associated with it, are global of nature. This means that the impacts caused by an emission are modelled in the same way regardless where on the surface of the earth, the emission takes place. There is therefore no relevance of including spatial variation in the source and receptor characteristics for this impact category. The characterisation factors are site-generic by nature and will be valid for EDIP97 (as an update) as well as for EDIP2003.

The atmosphere of the earth absorbs part of the infrared radiation emitted from earth towards space, and is thereby heated. This natural greenhouse effect can be said with certainty to have been increased over the past few centuries by human activities leading to accumulation of such gases as CO₂, N₂O, CH₄ and halocarbons in the atmosphere. The most import human contribution to the greenhouse effect is attributed to the combustion of fossil fuels such as coal, oil and natural gas.

The predicted consequences of the man-made greenhouse effect include higher global average temperatures, and changes in the global and regional climates. The world-wide network of meteorological researchers and atmospheric chemists, the IPCC (Intergovernmental Panel on Climate Change), is following the latest development in our knowledge of the greenhouse effect and issuing regular status reports. These status reports comprise the basis of the EDIP97 and EDIP2003 methodologies' assessment tool for the global warming.

The endpoint is chosen at the level of increase in the atmosphere's radiative forcing.

2.2 Classification

For a substance to be regarded as contributing to global warming, it must be a gas at normal temperatures in the atmosphere and:

be able to absorb heat radiation and be stable in the atmosphere for a period of years to centuries,
or
be of fossil origin and converted to CO₂ on breakdown in the atmosphere.

The criteria applied in the EDIP methodologies to determine if a substance contributes to global warming 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. At one point the EDIP method goes further than the IPCC's recommendation by including that contribution from organic compounds and carbon moNO_xide of petrochemical origin, which follows from their degradation sooner or later to CO₂ in the atmosphere. For emissions of CO₂ it is important to check whether they constitute a net addition of CO₂ to the atmosphere, or whether they simply represent a manipulation of part of the natural carbon cycle. If the source of carbon is fossil (coal, oil, natural gas), conversion to CO₂ will mean a net addition. If there is a question of combustion or breakdown of material which does not derive from fossil carbon sources, but e.g. from biomass, there will normally be no net addition because the material in question was generated recently by fixation of CO₂ from the atmosphere, and will sooner or later be broken down to CO₂ again (see Hauschild and Wenzel, 1998b, for a more detailed discussion).

The list of substances estimated to contribute to global warming is manageable and can be regarded as exhaustive. In other words, it is not necessary in practice to check whether a substance fulfils the criteria above in order to decide whether it is to be regarded as contributing to the greenhouse effect. It is sufficient to consult the list of greenhouse equivalency factors in Table 2.1.

2.3 EDIP2003 and updated EDIP97 characterisation factors

The endpoint for this impact category is chosen at the level of radiative forcing, and the EDIP2003 and revised EDIP97 characterisation factors are therefore taken from the latest version of the IPCC consensus report. These are complemented by factors for hydrocarbons and partly oxidised or halogenated hydrocarbons of fossil origin, which are derived from the stoichiometrically determined formation of CO₂ by oxidation of the substance. The recommendation for EDIP97 is still to use a time horizon of 100 years and to check the sensitivity to this choice by applying the other time horizons.

Table 2.1. Factors for characterisation of global warming (in g CO₂-equivalents/g). Taken from Albritton and Meira Filho, 2001 except as noted.

Click here to see the Table

2.4 Normalisation

The updated EDIP97 person equivalent for global warming is 8.7 t CO2-eq/pers/yr as found in Stranddorf et al., 2004.