How does water vapour contribute to global warming?

Question

How does water vapour contribute to global warming?

Answer 1

It provides the majority of the greenhouse effect.  But its' effect is constant, it can't INCREASE temperature by itself.

That's because the amount of water vapor in the atmosphere doesn't change.  Any excess just falls out as precipitation.

Excess CO2 can stay in the air for years, and it's been increasing steadily, so it's the cause of the INCREASE in temperature known as global warming.

A minor detail is that the increase in temperature due to CO2 makes the air able to hold more water vapor, making the temperature increase faster.

In scientific terms, water vapor can't be a forcing, but it is a feedback.

Answer 2

Tom P said:

"Water vapor does not contribute to global warming"

Wrong. Water vapor, as a feedback, accounts for the majority of the recent warming.

"but it is responsible for 90% to 95% of the greenhouse effect."

Wrong again. Water vapor itself accounts for 60-70% of the greenhouse effect.

"It is a very weak greenhouse gas"

This is very wrong. Water vapor is a very strong greenhouse gas.

Answer 3

Kindly note that clouds are not water vapor. Clouds do form from water vapor and water vapor does form from clouds. but in this context water vapor is a gas, while cloud is dispersed liquid.

Clouds do not differentiate much, they reflect all wavelengths, so have essentially  a negative effect on global warming... they reflect more sunlight than long wavelength light.

However, the gas, water vapor has only the slightest ability to reflect visible light or shorter frequency, while it significantly reflects long wave infra-red radiation. This very significantly defines it as a greenhouse gas.

We do get precipitation as water vapor builds up. but it is not at a constant water percentage of air. That is not as important as what happens when temperature is changing.

Water vapor condenses to form more cloud cover as we move to lower temperature globally. and we get less cloud cover as we warm up.

The effect on global warming is partly because we get more water vapor, but also because we get less cloud cover.

You have noticed that we get soil drying under a blazing sun. part of that is because we are getting heat retained by water vapor. and part is because we are getting more sunlight through as a result of reduced cloud cover.

So  water vapor has a bigger effect when earth's temperature is rising. Once earth starts to get a lot of cloud cover, almost all of our greenhouse gases will have far less effect.

It is, by the way, an ice age that will give us land bridges, by moving  mountains of water from the seas onto the land. Just think how much energy must have been available to evaporate that much water.

Answer 4

Water vapor does not contribute to global warming, but it is responsible for 90% to 95% of the greenhouse effect.  Water Vapor is a greenhouse gas like CO2, CFC's, HFC's, and methane.  It is a very weak greenhouse gas, but it occurs in such large quantities in the atmosphere that it is the most important greenhouse gas.  Without greenhouse gasses, our planets average temeprature would be about 30 degrees C cooler than it is right now.

Answer 5

Water Vapor is the predominant greenhouse gas. It is responsible for about 95% of the greenhouse effect. The remaining 5% consist of CO2 (3%), methane, and some other minor gases.

Remember that without the greenhouse effect we would never have existed. It is necessary for all life on earth.

Answer 6

Water Vapor is the main source of natural Global Warming, or Greenhouse Effect.  To note, the Bering Land Bridge which was available 11,500years ago has become submerged due to natural Global Warming.

The Water Vapor is not evenly distributed over the planet and is measured by a value of %RH or percent relative humidity.  The humidity is typically higher in places such as Texas or Florida...but folks in the Mid-West can attest to it being fairly high there as well.  Desert Areas typically see lower humidity.  So the impact of Water Vapor is anything but constant.

You can notice that overcast nights are warmer and overcast days tend to be muggier.  That is a very real effect of Water Vapor that people can see for themselves.

AGW or Antropogenic Global Warming is still very much a Theory as more accurate data is collected...the original forecasts have been halved more than 50% at least five times making the theory less than 3% accurate.  Another note, Pro-AGW folks tie AGW to the Industrial Revolution which began in the 1800s.

Global Warming is now referred to as Climate Change.  I guess the temperature hasn't cooperated much since the Theory first came out.  Climate Change affords wider lattitude in discussions, since it follows change rather than warming.

I haven't run across a Pro-AW site that even mentions Water Vapor in their discussions for Global Warming Gases...let alone percentages of atmospheric gases including Water Vapor.  The NOAA website below will tell you more about Water Vapor, Greenhouse Gases and Global Warming.

Answer 7

Water vapor is the BIGGEE in greenhouse gases.  It's evaporated off the surface and goes into the air and doesn't allow the sun's heat to flow back out into space as quickly.  

So the hotter we get, the more evaporate there would be floating around - and we'd get our globals warmed for sure!

Answer 8

CO2 is  380 parts per million of the air, this works out to 2 feet  per mile. Water vapour content varies  between 0 to 4%. at a median value of 2%, there would be 104 feet worth per mile.

     CO2 absorbs infrared at a few narrow wavelengths, water vapor  absorbs a much wider spectrum.

      You may have noticed that, on clear nights in

winter, the temperature drops rapidly. cloudy nights stay much warmer.

      If you read closely what the AGW believers say, you will find that they admit CO2 is a tiny effect.  They assume that that an increase in this tiny effect will result in an increase in water vapour, this will cause catastrophic runaway warming.

      They also assume that water vapour will have a positive feedback effect ( cause an increase), but it's much more likely to have negative feedback effects- more clouds will reflect sunlight away. also, water is very effective at transferring heat.  It absorbs heat at the surface, and evaporates, then it rises and condenses, thus transfering heat above most of the atmosphere.