The relative contributions to the greenhouse effect from the use of different fuels

An attempt has been made to assess factors that indicate how various fuels affect the climate. In these factors emissions of carbon dioxide, methane and nitrous oxide are weighed together with reference to the direct and indirect effects of these gases on the long wave radiation absorption.The analysis is dependent on the time period that is to be studied. We have carried out calculations both on the basis of the coming 50-year period and on the basis of a period where the greenhouse effect is summed up after the total lifetime of the gases in the atmosphere, i.e. more than 400 years.The analyses show that the results become different according to the time period considered.The uncertainties in the calculations are due to the following:

• ?the indirect effects of methane emissions, i.e. ozone formation, are difficult to assess;
• ?knowledge about the emissions of methane and nitrous oxide is incomplete;
• ?any other secondary effects such as emissions of carbon monoxide and other organic substances, natural and anthropogenic, may be of significance.

In addition, light should be shed on whether the results change significantly if account is also taken of the effects of the gases on the stratosphere, i.e. the depletion of the ozone layer.