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geordief

Water vapour as a greenhouse gas

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Are water vapour levels  broadly stable in the atmosphere? Is there any potential for them to rise with increases in global temperatures  and impart a feedback effect to any ongoing warming.

 

If so ,what timescales might we be talking about?

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Basically the water capacity of the atmosphere is temperature dependent. At higher temperature the water vapour rises. As water vapour is a greenhouse gas itself it can lead to feedback effects. 

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On 11/8/2018 at 9:54 PM, CharonY said:

Basically the water capacity of the atmosphere is temperature dependent. At higher temperature the water vapour rises. As water vapour is a greenhouse gas itself it can lead to feedback effects. 

Sorry I missed your reply.Could those effects be of any consequence or would they be minimal  for the most part?

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Just off the top of my head...
While CO2 bonds absorb radiation peaking in the infrared range, water molecule bonds absorb  radiation peaking in the microwave range.
So while the effects are of consequence, water vapor is not as efficient for the 'greenhouse' effect.

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The most important difference IMO is that CO2 stays in the atmosphere for thousands of years, whereas water vapor leaves the atmosphere every few thousand seconds each time it rains. 

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1 hour ago, MigL said:

Just off the top of my head...
While CO2 bonds absorb radiation peaking in the infrared range, water molecule bonds absorb  radiation peaking in the microwave range.
So while the effects are of consequence, water vapor is not as efficient for the 'greenhouse' effect.

But there can be a lot more of it, as compared to CO2

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6 hours ago, MigL said:

water molecule bonds absorb  radiation peaking in the microwave range.

Water has strong absorptions in the IR too.
It's a very effective greenhouse gas.

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Thanks John and Tom.
Never had the opportunity to look into that.
( so I said, off the top of my head )

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Would its effects be especially  noticeable  during the night?

 

Would a generalized increase in temperature lead to  local pockets with high humidity  leading to very hot nights  that might  prevent  sleep without air conditioning?

 

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On 11/3/2018 at 4:12 AM, geordief said:

Are water vapour levels  broadly stable in the atmosphere? Is there any potential for them to rise with increases in global temperatures  and impart a feedback effect to any ongoing warming.

If so ,what timescales might we be talking about?

It seems that any measurable temperature change (from a ‘forcing’ on the system) already includes the feedback from any change in water vapor, since it adjusts as quickly as weather changes rather than at a glacial pace.

Oxford Monographs on Geology and Geophysics, no. 16: Paleoclimatology; Crowley & North; 1991

sect.1.2 Energy Balance Models (EBMs) of the Present Climate; part 1.2.1 Radiation and Climate

Quote

 

Part of the upwelling radiation is intercepted and absorbed by layers of the stratified atmosphere primarily through triatomic trace gases such as H2O, CO2, and O3, as revealed in the absorption spectrum (Fig.1.3).  Carbon dioxide absorbs at about 2.7, 4, 10, and 14 μm; a water vapor continuum exists from ~12 to 18 μm; and so on.  Water vapor is the most important of these infrared absorbers.  Its concentration in the atmosphere is highly variable even on short (weather) time scales.  Its saturation vapor pressure also increases approximately exponentially as temperatures increase, with the vapor pressure of water roughly doubling for each increment of 10°C in the range of interest.  This is called the Clausius-Clapeyron relationship, and it is an important feature of the earth’s climate (and climate models).  It is an interesting fact that the relative humidity (ratio of actual concentration to the saturation value) appears to stay at an approximately constant value near 50% as the climate changes.

 

Climate Change Indicators: Weather and Climate   

Quote

 

Rising global average temperature is associated with widespread changes in weather patterns. Scientific studies indicate that extreme weather events such as heat waves and large storms are likely to become more frequent or more intense with human-induced climate change. This chapter focuses on observed changes in temperature, precipitation, storms, floods, and droughts.

U.S. and Global Temperature. Average temperatures have risen across the contiguous 48 states since 1901, with an increased rate of warming over the past 30 years. Eight of the top 10 warmest years on record have occurred since 1998. Average global temperatures show a similar trend, and all of the top 10 warmest years on record worldwide have occurred since 1998. Within the United States, temperatures in parts of the North, the West, and Alaska have increased the most.

High and Low Temperatures. Many extreme temperature conditions are becoming more common. Since the 1970s, unusually hot summer days (highs) have become more common over the last few decades in the United States. Unusually hot summer nights (lows) have become more common at an even faster rate. This trend indicates less “cooling off” at night. Although the United States has experienced many winters with unusually low temperatures, unusually cold winter temperatures have become less common—particularly very cold nights (lows). Record-setting daily high temperatures have become more common than record lows. The decade from 2000 to 2009 had twice as many record highs as record lows.

 

The extra heating, which is observed at nightas well as at higher latitudes and altitudes, is consistent with CO2 being the cause for the extra warming--as predicted.  If extra warming came from the sun, we wouldn't be seeing this sort of signature in the observations.

A warmer world, on average, holds more water vapor. 

Amazingly, it's about 7% more water vapor per each 1 degree C increase.  That's almost 4% more water vapor, per degree F of 'warming,' globally. 

~So, it's the heat and the absolute humidity!  

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If I have correctly understood then, the degree of saturation possible increases exponentially with temperature  even though relative humidity stays constant at 50%

 

Does this mean that the expected  humidity on any particular day  will also increase exponentially with temperature.?(since the upper bound does so)

 

Would it also be correct that ,whilst the greenhouse effect predicted already incorporates the level of water vapour concentration ,nonetheless the rather large ,non linear increase in humidity  might cause problems over above simple temperature levels?  (eg health problems due to inability to sleep  in vulnerable sections of the population)

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On 12/23/2018 at 6:58 AM, iNow said:

The most important difference IMO is that CO2 stays in the atmosphere for thousands of years, whereas water vapor leaves the atmosphere every few thousand seconds each time it rains. 

So you're saying that the age of a molecule affects its properties?  Old ones work better than new ones?  Clouds last only a "few thousand seconds"?

That doesn't sound like science to me.

1.  Water vapor has a broader IR spectrum than carbon dioxide, so the claim of "feedback" is utterly specious. 

2. Water vapor represents ~15,000 ppmv, versus ~410 ppmv for carbon dioxide.  

3.  The Keeling Curve is scientific fraud, designed to mislead and deceive, which science should never do.

Keeling Curve.jpg

`````scary-graph-including-water-vapor.jpg

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2 minutes ago, RenaissanceChemist said:

So you're saying that the age of a molecule affects its properties?  Old ones work better than new ones?  Clouds last only a "few thousand seconds"?

No one said any of those things. 

2 minutes ago, RenaissanceChemist said:

The Keeling Curve is scientific fraud, designed to mislead and deceive

Citation needed.

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On 12/23/2018 at 12:46 PM, John Cuthber said:

Water has strong absorptions in the IR too.
It's a very effective greenhouse gas.

 

atmospheric-absorption2.jpg

Just now, Strange said:

No one said any of those things. 

Citation needed.

Then whatever is your point about aging molecules?

Graph provided.  Point out any errors in modified graph.

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5 minutes ago, RenaissanceChemist said:

So you're saying that the age of a molecule affects its properties?  Old ones work better than new ones?  Clouds last only a "few thousand seconds"?

I’m saying water vapor comes back down rather often in a fascinating phenomena known as rain. Perhaps you’ve heard of it?

Carbon dioxide doesn’t do that. 

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1 hour ago, RenaissanceChemist said:

Then whatever is your point about aging molecules?

Residence time in the atmosphere. It has nothing to with aging molecules.

1 hour ago, RenaissanceChemist said:

 

1.  Water vapor has a broader IR spectrum than carbon dioxide, so the claim of "feedback" is utterly specious. 

What, precisely, is the connection between the two?

1 hour ago, RenaissanceChemist said:

2. Water vapor represents ~15,000 ppmv, versus ~410 ppmv for carbon dioxide.  

Can you finish the thought here? You’ve stated a fact but not explained why you think it’s relevant.

 

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7 hours ago, RenaissanceChemist said:

So you're saying that the age of a molecule affects its properties?  Old ones work better than new ones?  Clouds last only a "few thousand seconds"?

That doesn't sound like science to me.

1.  Water vapor has a broader IR spectrum than carbon dioxide, so the claim of "feedback" is utterly specious. 

2. Water vapor represents ~15,000 ppmv, versus ~410 ppmv for carbon dioxide.  

3.  The Keeling Curve is scientific fraud, designed to mislead and deceive, which science should never do.

I think you have just shown that you can't have a meaningful debate about an idea unless you understand it.

 

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8 hours ago, RenaissanceChemist said:

Graph provided Point out any errors in modified graph.

You mean the one where you have added the irrelevant (and unchanging) water vapour level in order to dishonestly hide the change in CO2 level? No, can’t see anything wrong with that at all. 

 

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@renaissanceChemist I think it is worthwhile reading the following two articles (or at least the first one which is relatively easy to read).

@other people in this thread, the read is maybe still interesting for a more in depth look into the science of CO2/H20 emissions.

The first article gives a nice explanation of the different spectra of H20 and CO2 and their greenhouse effects.

https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1002/wea.2072

https://geosci.uchicago.edu/~rtp1/papers/PhysTodayRT2011.pdf 

-Dagl

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Water vapour is a big contributor to the greenhouse effect.

But CO2 is the most important; because it's the one we have changed.

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4 hours ago, John Cuthber said:

Water vapour is a big contributor to the greenhouse effect.

But CO2 is the most important; because it's the one we have changed.

To expand on this, water vapor is one of the reasons we are not an iceball of a planet. It has a massive impact on the greenhouse effect. But the phenomenon of global warming is distinct from this baseline warming.

 

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