However, as the temperature increases, other aspects of the climate will alter, including the amount of water vapor in the atmosphere. While human activities do not directly add significant amounts of water vapor to the atmosphere, warmer air contains more water vapor. Since water vapor is itself a greenhouse gas, global warming will be further enhanced by the increased amounts of water vapor. This sort of indirect effect is called a positive feedback. However, observations of the current atmosphere provide evidence for the conclusion that on a global scale, a warmed atmosphere will moisten and this will enhance greenhouse warming.
Clouds are another important factor in determining climate.
The increased levels of water vapor in the atmosphere, as well as changes in temperatures and winds, will also cause changes in clouds that will alter the amount of energy from the sun that is absorbed and reflected by the Earth, at some locations enhancing and at others diminishing the warming due to greenhouse gases. The response of clouds to global warming is a major uncertainty in determining the magnitude and distribution of climate change.