Clouds and climate models

I have had heated discussions with climate change deniers, them saying that climate change is a hoax, since climate models do not take cloud effects properly into consideration. According to them, it is clear that clouds cause cooling, and if they were included, the models would not predict global warming. As evidence for their claim, they give the cooling caused by clouds formed by volcanic eruptions, and the decrease in temperature when the sunshiny day turns into cloudy one. Further, they maintain that whenever temperature increases, clouds will be formed causing cooling.

Climate models include clouds, but  because different cloud types, their stability and distribution affect climate in different ways, the uncertainties of the models are markedly increased by them. Further, contrary to what climate change deniers say, temperature increase is not associated with cloudiness and consecutive cooling. In fact, it appears that warming causes changes in clouds and cloudiness, which further increase temperature.

The effects of clouds on climate models are difficult to estimate, because cloud altitude, the thickness of cloud, and the nature of the small particles (aerosols) gathering the moisture needed to form clouds all affect the temperature effects of clouds. For example, low-lying clouds can actually increase temperature, as they trap the heat, and prevent it from escaping; this is best seen in cloudy nights, which are much warmer than clear nights. In contrast, clouds at high altitudes have little heat-trapping capacity but, depending on the nature of particles in the cloud, effectively reflect sunlight thereby effectively cooling the atmosphere below. The particles in the clouds can be either reflective or absorptive, and cloud formation and dissolution give additional problems for climate models.

Consecutively, clouds are presently the largest uncertainty of climate models. However, regardless of the cloud input, the models show that climate change is occurring. Furthermore, the models have improved considerably in the recent past, as both the cloud behaviour is understood better and the computing power has increased. The uncertainties of climate models caused by clouds can further decrease as a result of theoretical and experimental studies on them.