Evaporation Feedbacks

The Hydrologic Cycle

The hydrologie cycle is part of this heat energy imbalance process. This feedback process complicates the global warming phenomena and involves water vapor, clouds, and aerosol particles. Evaporation is the basis of this important process. Water is evaporated by Sun, incorporated into clouds as water vapor, falls to the land and water bodies as rain, and enters water bodies to complete the cycle. Conversely, to make matters worse, water vapor acts as a prominent greenhouse gas as it is involved in an important climate feedback loop. Due to ascending evaporation from water bodies, the water vapor amount in the atmosphere increases.

The additional water vapor absorbs radiated thermal infrared energy that would otherwise escape from Earth's surface to outer space, and radiates the heat back to the Earth again. Thus, it makes the Earth's surface even warmer. This somber picture is further complicated by important interactions among water vapor, clouds, atmospheric motion, and radiation from both the Sun and the Earth.

Moreover, continuous increases of the Earth's surface temperature augments the sea or ocean surface temperature. Therefore, increased evaporation and higher annual rainfall amounts should occur. Computer simulation models found that a global warming of 7.2 degrees F (4 degrees C) is expected to increase global evaporation and precipitation by about 10 percent. Scientists found through models that the upper tropospheric water vapor amount will increase by 15 percent with each degree of atmospheric temperature rise, because of increased evaporation.

Another evaporation feedback mechanism involves the atmospheric wind-evaporation-convection feedback in the tropics. The feedback is shown to be very effective in channeling perturbations from one component of the climate system to other components, such as from evaporation to surface wind, and from atmospheric convective activity to evaporation. Through this feedback process, it is also observed that surface evaporation over tropical oceans is connected with cloud absorption of shortwave radiation. Diminished shortwave absorption by clouds causes excessive shortwave radiation at the Earth's surface, leading to excessive evaporation. As the loop continues, the Earth's surface gets warmer and warmer.

...