Climate models are very complex, and one part of the models that is especially difficult to get correct is how the models handle clouds. Clouds tend to be smaller than the grid size of the models and reach to different wavelengths of light in different ways. High clouds during the day can cool things off slightly. Climatologically, this even shows up along the major flight paths of airports like Chicago’s O’Hare, where contrails from the arriving and departing flights causes cooling underneath the glide paths. Clouds at night trap heat from the ground near the surface, keeping it warmer, so it is harder to get a surface freeze when the sky is very cloudy. This story from The Week describes why getting the clouds correct in the models is a key to getting accurate climate projections.
