[lilsis]

I do not believe that human contribution to global warming is significant.

Water vapor is responsible for 95% of the greenhouse effect, yet somehow it is never brought up in global warming discussions. Why is this?

We've raised CO2 concentrations 100 ppm to 370 ppm... a concentration that's tiny in comparison to the amount of water vapor in the atmosphere... after all, we're on a giant ball of water.

I subscribe to the theory of giant ball of nuclear fire leads to warmer temperatures -> increase in ocean temperatures -> release of dissolved CO2 & increase in water vapor -> greater greenhouse effect

I don't hate the environment and obviously we should be reducing our impact, but cleaner air and water should be cause enough.

If anyone can explain to me why my reasoning is flawed I'll be happy to champion the idea that global warming is primarily driven by man... it would actually make my life easier to embrace it as fact. However, as it stands now, it seems to me a rather arrogant proposition.

[lutorm]

It doesn't matter if 99.9% of greenhouse effect is not caused by humans, if the extra 0.1% is. The gross heat fluxes in and out are enormous, but because they precisely balance they're not noticeable. An extra 0.1%, while very small compared to the total heat flux, is a purely net flux because it's not canceled out (until the Earth has warmed). It's simple conservation of energy.

Think of it this way: If you have a gallon of water and you pour it back and forth between two containers, you will eventually run out of water even if you lose only a few drops each time.

Another example: If you trade your assets back and forth between different stocks (and they don't change value), it doesn't matter how much money you start with, if you do it for long enough you will eventually run out of money due to the transaction cost.

A small effect can have a big impact if it's allowed to accumulate over time, and that's precisely what's happening with the greenhouse effect.

[lilsis]

This is a good argument assuming that the Earth's heat fluxes are in balance, but I don't believe this to be the case, what with ice ages, etc.

[lutorm]

Btw, the fact that the major greenhouse gas is water vapor does not make things better, it makes them worse. It means there's a feedback loop that amplifies the effect of increased CO2, because as the world warms, the atmospheric concentrations of H2O will increase, further increasing the warming.

[philwelch]

"Water vapor is responsible for 95% of the greenhouse effect, yet somehow it is never brought up in global warming discussions. Why is this?"

Because the water vapor isn't what's increasing, except as an effect of the warming trend caused by higher CO2 concentration.

"I subscribe to the theory of giant ball of nuclear fire leads to warmer temperatures -> increase in ocean temperatures -> release of dissolved CO2 & increase in water vapor -> greater greenhouse effect"

Care to explain why the sun progressively got hotter in a way that strongly correlates with the release of CO2 since the Industrial Revolution?

[adnam]

> Water vapor is responsible for 95% of the greenhouse effect

"For clear skies, water vapor is the most important greenhouse gas, accounting for 60% of the total. The second most important greenhouse gas is CO2, which contributes 32 W m−2"

See "Earth’s Annual Global Mean Energy Budget", page 203 (7th page of PDF): http://www.atmo.arizona.edu/students/courselinks/spring04/at...

[lilsis]

Good source, thanks for sharing.

From the DOE...

"Given the present composition of the atmosphere, the contribution to the total heating rate in the troposphere is around 5 percent from carbon dioxide and around 95 percent from water vapor."

It is important to note the next sentence, however:

"In the stratosphere, the contribution is about 80 percent from carbon dioxide and about 20 percent from water vapor."

http://www.eia.doe.gov/cneaf/alternate/page/environment/appd...

(end of last paragraph)

As is always the case in these matters, conflicting sources

Not being an atmospheric scientist I cannot be sure but I feel like the vast majority of the atmosphere's density being in the troposphere temperature effects from the stratosphere would be negligible.