The researchers aimed to choose the best climate models to predict future climate in Western North America. They selected four models for each of two possible future scenarios (based on greenhouse gas levels) that accurately reflected past climates and predicted changes in temperature and rainfall. By comparing these models to historical data, they selected models that represented a range of possible climates, from very wet and warm to dry and cold, giving a comprehensive picture of potential future conditions in the region. This helps in planning for the impacts of climate change in Western North America.