The method of the ecological scarcity method weightes different ressources and emissions according to their ecological factors. An ecological factors is based on three characteristic: characterisation, normalisation and weighting. 

characterisation: In a first step, harmful substances get a characterisation factor on how damaging they are to the environment. For example, harmful susbtances that contribute to climate change get a characterisation factor according to the IPCC report also called climate change potential. 

normalisation: is sometimes optional and calculates an impact relative to a chosen reference. The goal is to present the number in an uniform, dimensionless unit like a fraction of a person's yearly impact. 

weighting: it weights different environmental factors, so that it is possible to present the LCA result in a single score. This allows to compare the environmental impact of different products. It is important to be aware of the reasoning of the environmental impact factors. One method, is the distance to target method, when the goal of a country is to reduce CO2 emissions by 50% and to reduce SO2 emissions by 20%, the climate change impact factor will get a higher weighting.