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:Furthermore, for thin clouds under pristine conditions, as often found in the Arctic, increased particle concentrations due to pollution can lead to clouds that increase surface warming from longwave emission (Garrett et al., 2002; Garrett and Zhao, 2006; Mauritsen et al., 2011).
Category: