Water Vapour : Culprit for Global Warming

A little surprising isn't it, expert says water vapour is the main villain behind rapidly increasing temperature.Evaporated H20 is a known greenhouse gas -a gas that absorbs and re-emits infrared radiation in Earth's atmosphere, thereby increasing temperatures.By mass and volume, water vapor is the most prevalent greenhouse gas in the atmosphere.
The skeptical argument thus goes something like this: Since water vapor is the most potent greenhouse gas, and since this vapor is created through natural evaporation rather than human activity, the current warming trend is nothing to worry about—just the Earth going through a normal climatic cycle.
But this viewpoint ignores the reactive nature of water vapor—in other words, the gas doesn't cause warming all by its lonesome. The amount of water vapor the atmosphere can hold is almost purely a function of temperature—the warmer the air gets, the more vapor it's able to glean from the planet.
We know, for example, that the atmospheric water content over the oceans has increased (PDF) by 0.41 kilograms per square meter every 10 years since 1988. So, what's causing the temperature rise that's resulted in greater evaporation? Well, over that same time period, global emissions of carbon dioxide have soared.
And unlike water vapor, which returns to Earth as precipitation within a week of entering the atmosphere, CO2 sticks around for between 50 and 200 years.
Carbon dioxide accounts for approximately 25 percent of the greenhouse effect, so it's pretty clear that the dramatic increase in atmospheric CO2 is playing a significant role in recent warming. (This warming might have been even greater if not for the ability of the planet's oceans to absorb heat.)
Warmed by CO2, the atmosphere is thus able to absorb more water vapor. And that water vapor, in turn, causes further warming—it amplifies the effects of carbon dioxide. So anthropogenic CO2 serves as the chief engine of global warming, with water vapor playing a crucial secondary role.