Refers to the idea that emissions reductions anywhere within a specific area count toward compliance. For example, if a plant with multiple emissions sources is treated as being “under a emissions bubble”, regulators assess only the total emissions of the plant, not the emissions of each individual source, in determining compliance. Bubble also refers to an option in the Kyoto Protocol that allows a group of countries to meet their targets jointly by aggregating their total emissions. The member states of the European Union are utilizing this option.