Climate change is a gradual change in the global temperature caused by the accumulation of greenhouse gases in the atmosphere. Carbon dioxide is the most significant greenhouse gas and results from the generation of electricity, generation of steam and combustion of fuels. A small amount of carbon dioxide is also emitted from fermentation operations. The other greenhouse gases include methane emitted from waste treatment and halocarbons, emitted from production operations and ancillary cooling systems.

GSK reports carbon dioxide, including CO₂ equivalents, in million kilograms. For CO₂ related to energy, GSK includes electricity imported (not generated onsite), steam imported (not generated onsite) and combustion of fuel used for non-transport related activities (e.g. onsite generation of electricity and steam). The 2001 CO₂ from energy sources baseline was originally reported as 1,950 million kilograms. The calculations resulting in this value were reviewed as part of the data reporting and analysis process this year. Incorrect application of CO₂ conversion factors, the incorrect inclusion of site-based transport fuels and double counting the fuels used onsite to generate steam and electricity were uncovered making a change to the 2001 baseline necessary. This new 2001 baseline is 1,694 million kilograms. For 2002, the CO₂ generated from these energy sources is 1,631 million kilograms representing a 3.7% decrease. Carbon dioxide generated from non-transport fuels, production of imported steam and production of imported electricity decreased by 4.7%, 92% and 0.4% respectively.

In 2001, GSK set an improvement target of 8% reduction on a per unit sales basis by the end of 2005 for CO₂ from these energy sources.

Carbon dioxide is the most significant greenhouse gas and results from the generation of electricity, generation of steam and combustion of fuels. The other primary greenhouse gases include methane, nitrous oxide, hydrofluorocarbons, perfluorcarbons and sulfur hexaflouride. Greenhouse gases such as CO₂ and methane are formed from waste treatment and fermentation. Halocarbons are released during production operations and from ancillary cooling systems. These other greenhouse gases can be compared to carbon dioxide by calculating their CO₂ equivalence. Included in the global warming potential figure in this graph is carbon dioxide generated from energy sources (see summary on carbon dioxide), CO₂ equivalents from halocarbons (ozone depleting substances) and CO₂ equivalents from waste treatment and fermentation.

Inventory methods and factors utilised for conversion to carbon dioxide equivalents are based on the World Business Council for Sustainable Development (WBCSD)/ World Resources Institute (WRI) Greenhouse Gas Protocol Initiative, September 2001, its Stationary and Mobile Combustion Workbooks, and the Intergovernmental Panel on Climate Change (1996).

GSKs total global warming potential expressed in carbon dioxide equivalents, was reported as 3,363 million kilograms in 2001. In light of the baseline changes made to CO₂ from energy there is also a revised 2001 baseline for total global warming potential of 3,154 million kilograms. In 2002, the total global warming potential is 2,854 million kilograms representing a 9.5% decrease.