*2.4. NDP026*

We reanalyzed the ground-based total cloud cover observations in Numeric Data Package NDP06 [26], following methodology outlined in Warren et al. [27]. Briefly, the methodology consists of estimating seasonal trends at each of the stations, then averaging these trends over a 10 × 10 degree grid. We compared these estimated trends with those predicted by CMIP5 models for the period of 1971–2005 using a chi-squared test for independence. Several modeling studies showed the connection between low clouds over land and increased levels of CO2 in the atmosphere [28,29]. As such, it would have been more appropriate to use changes in low cloud cover in our analysis. However, CMIP5 did not mandate modeling teams to submit low, medium, and high cloud simulations separately. Only total cloud cover was required from the modeling teams, hence we used total cloud cover data in our analysis.
