Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:, 2003] and visibility [Seinfeld and Pandis, 2006] and can also influence Earth’s energy balance either directly [Intergovernmental Panel on Climate Change, 2007] or through the modification of cloud properties [Twomey, 1977; Albrecht, 1989].
Category: