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You are here: UMWiki>WaterVapor1 Web>WebHome (28 Sep 2008, colle034)
<p align="right" style="text- Global climate change is an issue that needs to be addressed, however with so many different inputs that affect climate change, it is hard to do so. The Intergovernmental Panel on Climate Change (IPCC) recently reported that within the last 50 years, most of the observed greenhouse effect can be attributed to human activities, (Crosson, 2008). "Methane, water vapor, and carbon dioxide are collectively responsible for the majority of the Earth's greenhouse effect," (Crosson, 2008). Table 1 shows the relationship of water vapor compared to other greenhouse gases as it contributes to the greenhouse effect.

Many scientists view water vapor as positive feedback, some argue that it can be negative, but nothing that has been presented in recent years. It is a positive feedback because scientific atmospheric models show a constant relative humidity in direct respect to increasing temperatures within the tropical troposphere, which implies an increase in specific humidity or otherwise known as water vapor (Gettelman, 2008). Upper-tropospheric water vapor feedback is perhaps the most important type, since a change in the state of the climate changes the water vapor. Water vapor is the highest percentage content in all of the greenhouse gases, which is why if there is a great change in temperature it is further going to increase the water vapor content and create a snowball effect of increasing temperatures.

“The water vapor feedback arises largely from the tropics where there is a nearly moist adiabatic profile,” (Gettelman, 2008). If the relative humidity is unchanged due to the moisture arising from the oceans and convection to the upper troposphere, then the water vapor will increase (2008). Most of these observations were made from community atmosphere models, infrared sensors and satellites. Through lots of observations and scientific tests, it was determined that specific humidity or water vapor increases from the response of increasing surface temperatures in order to maintain the relative humidity rate (Gettelman, 2008). “The increase in temperature scales is like a moist adiabat, with increases larger at higher altitudes” (Gettelman, 2008). Since there are lower pressures at higher altitudes with larger increases of temperatures, scientists suggest that the structure of the tropics are changing, including rising levels of moisture at higher altitudes and higher levels of subsidence at lower altitudes (Gettelman, 2008). Through the atmosphere models and satellite data, there is confidence that there is lots of climate sensitivity due to the positive feedback effect from water vapor.

Water vapor feedback works when transpiration and evaporation are produced from short wave radiation absorbing through the Earth’s surface to warm the environment. This moist atmosphere produces a layer above the Earth’s surface which then reflects the majority of the long wave radiation back to the surface, thus creating warmer temperatures. Although this is necessary for the survival of all mankind, temperatures are beginning to increase too much from the release of high amounts of greenhouse gases. Some of these gases naturally occur in the environment, such as methane, nitrogen and carbon dioxide, however, the exhaust from cars and industry smokestacks increase these by the process of the greenhouse effect. The warming temperatures resulting from this, constantly circulates with water vapor by increasing the specific humidity. Warmer temperatures produce more and more evaporation and transpiration, which increase this layer of entrapping long wave radiation.

"The equilibrium climate sensitivity is a measure of the climate system response to sustained radiative forcing," (IPCC, 2007).

Table 1. Contribution of water vapor to greenhouse effect (Global Warming)

References:

肻x{fffd}\x{fffd}肻x{fffd}路 Gettelman, A. and Fu, Q. Observed and Simulated Upper-Tropospheric Water Vapor Feedback. American Meteorological Society. Volume 21, Issue 13 (July 2008), pp. 3282–3289.

肻x{fffd}\x{fffd}肻x{fffd}路 Crosson, E.R. A cavity ring-down analyzer for measuring atmospheric levels of methane, carbon dioxide, and water vapor, Applied Physics B: Lasers and Optics. Volume 92, Number 3. (September, 2008) pp. 403-408.

肻x{fffd}\x{fffd}肻x{fffd}路 Global Warming: A closer look at the numbers. Modified: January 10, 2003. http://www.geocraft.com/WVFossils/greenhouse_data.html Visited: September, 16, 2008.

肻x{fffd}\x{fffd}肻x{fffd}路 IPCC, 2007 . Fourth Assessment Report. Cambridge University Press, London

肻x{fffd}\x{fffd}肻x{fffd}路 Schneider, Edwin K. Tropospheric Water Vapor and Climate Sensitivity. Journal of the Atmospheric Sciences. Volume 56, Issue 11. (July, 1998). pp. 1649–1658

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pdfpdf Tropospheric_Water_Vapor_and_Climate_Sensitivity.pdf manage 164.1 K 17 Sep 2008 - 12:55 UnknownUser Climate Sensitivity Article
Topic revision: r4 - 28 Sep 2008 - 20:52:01 - colle034
 
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