Climate, water vapor feedback

In Eq. (LL), A// is the heat of vaporization of water and R is the gas constant. Thus the vapor pressure of water has an exponential dependence on temperature. This suggests that there may be a water vapor feedback associated with global climate change. If the atmosphere warms, for example due to increased greenhouse gases such as C02, increased concentrations of gaseous water are expected in accordance with Eq. (LL). The increased water vapor traps more thermal infrared radiation, warming the atmosphere further (e.g., Raval and Ramanathan, 1989 Stenchikov and Robock, 1995). 

Hall A., Manabe S. (1999) The role of water vapor feedback in unperturbed climate variability and global warmingj. Clim. 12, 2327-46. 

H20 Greenhouse Feedback. As the lower atmosphere (the troposphere) warms, it can hold more water vapor. The enhanced water vapor traps more IR radiation and amplifies the greenhouse effect. Ramanathan [36] indicates that, based on studies with one-dimensional climate models, this feedback amplifies the air temperature by a factor of about 1.5 and the surface warming by a factor of about 3. The IPCC [23] determined a surface temperature amplification factor of 1.6 for water vapor feedback. 

Wordsworth et al 2010 [367] made a three dimensional global circulation model (GCM) of the early martian climate. In their model CO2 condensation, cloud formation and a water cycle was included. Local water vapor feedbacks compensate reduced CO2 warming effects. In general CO2 clouds lead to a substantial warming. 

One such feedback is the influence of clouds and water vapor. As the climate warms, more water vapor enters the atmosphere. But how much And which parts of the atmosphere, high or low And how does the increased humidity affect cloud formation While the relationships among clouds, water vapor, and global climate are complicated in and of themselves, the situation is further complicated by the fact that aerosols exert a poorly understood influence on clouds. 

The nature of such processes can be depicted as a feedback loop, as shown in Fig. 17-4. Using the nomenclature in this figure and continuing with enhanced evaporation of water vapor as our physical example of a feedback that is completely internal to the climate system, we... 

High atmospheric COj leads to fester evapotranspiration rates, providing another mechanism by which water vapor levels increase. This is singularly important as water vapor changes are now recognized by the IPCC as the largest feedback affecting climate sensitivity. 

K (W m-2)-1, this would lead to an increase in the global mean temperature of A Te — 1.4 K. This temperature increase is less than what climate models predict because of feedbacks that act to enhance warming. As noted earlier, such feedbacks include, for example, the fact that a warmer atmosphere contains more water vapor, and hence an enhanced infrared absorption. 

In general, then, surface temperature changes are predicted to be 1-4 times larger if climate feedbacks are included. The increase in atmospheric water vapor provides the... 

For weather prediction in the polar areas, it is important to take into account the effects of sea ice. Approximately 2% of the total water on the earth is stored in the form of ice in polar areas and glaciers. Sea ice accounts for nearly two-thirds of the earth s ice cover in areal extent. Sea ice plays the major role of controlling the exchange of heat, water vapor, and momentum between sea and air in the polar regions. Ice cuts off heat and water vapor transport from the ocean to the atmosphere and increases the albedo. Thus, similar to snow cover over land, sea ice contributes to cooling over the ice surface, which, in turn, tends to thicken the ice— a positive climatic feedback. 

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