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Climate change denier myth 04: Water vapor is a stronger GHG than CO2, therefore water emissions matter more
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2017 Mar 31, 3:14am 1,936 views 6 comments
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FNWGMOBDVZXDNW
2017 Mar 31, 11:19am
Water vapor also has other effects, such as cloud formation and clouds can reflect heat too, so quantifying the impact is difficult.
Nope, it's not
The feedback loop in which water is involved is critically important to projecting future climate change, but as yet is still fairly poorly measured and understood.
Your source is confirming what I said. Quantifying the effects of water is hard, but it is done with models, and they tell us that water has a warming impact.
So, as warm temperatures lead to more water vapor in the air, more water vapor in the air leads to warmer temperatures, which creates a positive feedback loop.
This also confirms what I stated here:
YesYNot says
The easiest way for us to increase the amount of water vapor in the atmosphere is to increase the temperature by emitting GH gases, and this will increase the amount of evaporation and decrease the amount of condensation. Modest changes in temperature have a big impact on saturated vapor pressure, which makes this positive feedback effect important.
Another way to state this is that water vapor has an amplifying effect increasing the impact of greenhouse gases, which your source states here: Ironman says
New study confirms water vapor as global warming amplifier
I could go on and on. They even confirm what I said about the warmer air being able to hold more water vapor. It's almost as if you are trying to lose this debate. The problem is that you don't even understand that your sources are supporting my argument.
You are citing mainstream global warming theory, none of which implies that CO2 emissions are less important and that water emissions are more important. In fact, this one states that the impact is not a direct result of industrialization (emissions of water) Ironman says
However, changes in its concentration is also considered to be a result of climate feedbacks related to the warming of the atmosphere rather than a direct result of industrialization.
FNWGMOBDVZXDNW
2017 Mar 31, 11:26am
In another thread, I stated that the amount of water vapor in the atmosphere was a function of temperature and explained the feedback loop (amplification effect). You just argued with me as the discussion sailed over your head. Here's the funny thing: Because you didn't understand the discussion the first time, you didn't realize that the sources you are posting now are just confirming exactly what I said.
https://patrick.net/1304501/2017-03-30-chemistry-expert-carbon-dioxide-can-t-cause-global-warming?c=1395022#comment-1395022
https://patrick.net/1304501/2017-03-30-chemistry-expert-carbon-dioxide-can-t-cause-global-warming?c=1395045#comment-1395045
FNWGMOBDVZXDNW
2017 Mar 31, 11:33am
Is water a far more important a greenhouse gas than carbon dioxide, as some claim?
There is a difference between being an important greenhouse gas and being an important greenhouse gas emission. That is the point that you seem to be missing.
FNWGMOBDVZXDNW
2017 Mar 31, 11:53am
What specifically about my original post do you think is wrong?
FNWGMOBDVZXDNW
2017 Mar 31, 12:01pm
What have you cited so far that mentions emissions of water? The answer is nothing. There are plenty of places that state that when the planet warms, it increases the water vapor in the air, and that that amplifies any warming that happens. That is exactly what I wrote and is consistent with the fact that humans emitting water vapor have negligible impact on the climate.
FNWGMOBDVZXDNW
2017 Mar 31, 12:04pm
CO2, CH4, etc emissions don't heat the planet directly. They heat the planet by absorbing radiation from the earth and keeping that heat on the planet. This heating is amplified by the fact that the higher temperatures cause increases to the amount of water vapor in the air. So, it just provides another mechanism to increase the impact of global warming emissions. If the impact of water is found to be higher than previously thought, it will just accelerate the temperature increases predicted by global warming models.
Water vapor is a strong GH gas and absorbs more radiation energy than CO2. Water vapor also has other effects, such as cloud formation and clouds can reflect heat too, so quantifying the impact is difficult. However, models tell us that on the whole, increased water vapor increases global temperatures. So, it is reasonable (although wrong) that people would think that emitting water was as damaging as emitting CO2.
CO2, CH4, and N2O, etc. are non-condensable gases. When you put these up into the atmosphere, they either react to form other chemicals or stay up there. For example, CH4 will oxidize and form CO2. These reactions can be with other gases in the atmosphere (more likely with methane) or on earth. CO2 is very stable in the atmosphere, but plants absorb it and convert it (react it with water) to make sugars and other things. Because it is non-condensable and stable, CO2 will stay in the atmosphere for a long time. That is why we have been able to increase the amount of CO2 by over 33% in the short time that we've been burning fossil fuels.
Water is a condensable gas. When the temperature cools below the dew point (function of amount of water in atmosphere), water will condense out. For this reason, water doesn't stay in the atmosphere for a long time at all. Water is constantly being evaporated over water bodies and condensed out when the warm saturated air cools. The amount of water in the atmosphere can be expressed as a mole percent or ppm like CO2. However, it is much more useful to express it as a percent relative humidity. The relative humidity is the amount of water vapor (partial pressure) divided by the saturated vapor pressure. This will always be between 0 (where there is no water source) and 100% (usually high near water sources)
The saturated vapor pressure is a function of temperature. This is well known, and should not be a point of debate. There are many ways to parameterize the vapor pressure curve. The Antoine is commonly used, and that is: log P = A-B/(C+T). Note that this is a function of temperature. If the temperature goes up, then the amount of water in the air at 100% humidity will go up, and the atmosphere will be able to hold more water vapor before condensing it out. As the average temperature of the earth heats up, then the average amount of water in the atmosphere will go up with it. Saturated water pressures are available without equations in steam tables (or saturated water vapor tables), one of which can be found here: https://en.wikipedia.org/wiki/Vapour_pressure_of_water. You can see that increasing the temperature from 77 to 86 oF increases the saturated pressure by about 34%. So, the impact on vapor pressure is large for relatively modest increases in temperature.
To summarize: We can directly put water vapor in the air and not have a long term impact on the amount of water in the atmosphere, because it just condenses out. The global temperature, however, does have a significant impact on the amount of water vapor in the air by changing the saturated vapor pressure (amount at 100% humidity). CO2 and CH4 on the other hand stay in the atmosphere for a long time, and when we put these into the atmosphere, we can have a large impact on the amount there. The easiest way for us to increase the amount of water vapor in the atmosphere is to increase the temperature by emitting GH gases, and this will increase the amount of evaporation and decrease the amount of condensation. Modest changes in temperature have a big impact on saturated vapor pressure, which makes this positive feedback effect important.
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