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:Whether Arctic clouds have a net warming or cooling effect depends on the time of year and location (Garrett et al., 2002; Garrett and Zhao, 2006; Lubin and Vogelmann, 2007; Sedlar et al., 2010; Shupe and Intrieri, 2004; Tjernström, 2005; Wang and Key, 2003).
Category: