3
$\begingroup$

As is reported on the major news networks, many glaciers and big icebergs are melting, which reportedly causes a tremendous increase in the amount of water vapor in the atmosphere.

Now a lot of water vapor and the increasing heat from the sun powers stronger storms and greater inequalities in the distribution of water throughout the world. Therefore, there are more incidences of drought in some places and big flooding in others. I think it all relates back to the fact there are millions of tons more water vapor in the atmosphere. This, added with the Sun's heating, will make more intense storms.

My question is, given all the talk of global warming and instabilities in the weather why isn't the fact that there is a tremendous amount of extra water vapor in the atmosphere ever mentioned on the news or on other TV shows?

Improve this question
$\endgroup$
5
  • 3
    $\begingroup$ your line of reasoning is flawed. When glaciers melt they create water... not water vapor. Water vapor increasing in the air is mostly defined by temperature. $\endgroup$
    – f.thorpe ♦
    Sep 8, 2014 at 6:06
  • $\begingroup$ With all the melting Glaciers and icebergs etc, of course they create water that is added to rivers and lakes and the Oceans yet all that extra water 'joins' in the evaporation cycles and adds a lot of EXTRA water vapor to the atmosphere. With all the extra melting of ice going on where does all the water go , and after evaporation where does all the extra water vapor go? $\endgroup$
    – user128932
    Sep 8, 2014 at 6:11
  • 3
    $\begingroup$ Moisture in the air is limited by temperature and pressure - if either get too low, the water will precipitate out. Extra melting does not necessarily imply extra evaporation. Water doesn't evaporate much at temperatures just above freezing. Also, melting ice actually absorbs a lot of heat from its surroundings (required to make the phase change to water), and in doing so, would cool the surrounding air, lowering the dew point, and potentially reducing the amount of moisture in the air. $\endgroup$
    – naught101
    Sep 8, 2014 at 13:36
  • $\begingroup$ If say as a terrible guess 1 billion tons of water is formed by ice in one month in the Northern Hemisphere and after a certain time period most of it evaporates where does it go? You can't be suggesting the amount of water vapor in the atmosphere has been going up and down over the last few decades but on average has been stable. Lots of extra water being formed eventually evaporating yet the average water vapor in the atmosphere is not going up. This seems illogical. $\endgroup$
    – user128932
    Sep 10, 2014 at 5:26
  • 1
    $\begingroup$ @user128932 It goes into the oceans and contributes to sea level rise. $\endgroup$
    – gerrit ♦
    Sep 17, 2014 at 15:29

3 Answers 3

Reset to default
13
$\begingroup$

Extra water doesn't mean extra water vapor. Even without this EXTRA water, the water vapor levels will increase, in the current warming world. As its the temperature rise that is making the water turn to vapor.

As temperature rises, evaporation increases and more water vapour accumulates in the atmosphere. As a greenhouse gas, the water absorbs more heat, further warming the air and causing more evaporation. When CO2 is added to the atmosphere, as a greenhouse gas it has a warming effect. This causes more water to evaporate and warm the air to a higher, stabilized level. So the warming from CO2 has an amplified effect. Water vapor is infact the largest positive feedback in the climate system (Soden 2005). - Skeptical Science

Intensification of the water cycle hence, is a product of rise in temperature, rather than the water content. Of course we need water to evaporate, but the increase in the water content doesn't correlate to increased water vapor. It might play some role locally in small ponds and seasonal rivers which get dry during summers, but on a global scale with most of our evaporation occurring over oceans (86% of global evaporation), its not significant enough.

So coming to your question. First of all its not like water vapor is never mentioned -

As global temperatures rise, the atmosphere then holds more moisture ... Therefore there is more water vapor available to fall as rain, snow. - thinkprogress.org - September 5

Global warming is moistening the atmosphere - The Guardian - August 13

And if you notice, all the recent news about melting glaciers has been in connected to some recent developments and observations in form of published papers at reputed journals. NASA even conducted a press conference explaining their latest research, which led to a series of news articles on the topic. So, i'm quite sure if there are some significant developments in terms of water vapor research, it will make the news as well.

Improve this answer
$\endgroup$
2
  • $\begingroup$ So global warming is moistening the atmosphere according to the Guardian. Does that mean the water vapor levels in the atmosphere are rising? $\endgroup$
    – user128932
    Sep 10, 2014 at 5:32
  • $\begingroup$ Yes. If you read the article, that is what they meant by moistening. But i also see that they are only considering vapor levels the 'upper atmosphere' and its implications on climate. Also Guardian is just stating this study. (pnas.org/content/111/32/11636.abstract). $\endgroup$
    – Vikram
    Sep 10, 2014 at 8:51
13
$\begingroup$

Your reasoning is a bit flawed.

The immediate effect of melting of the ice sheet is to add a small amount of water to the oceans (here small is relative to the huge amount of water already in the oceans). Over time, this small effect will result in sea level rise, currently estimated to be a rise of 50 to 200 centimeters by the end of this century.

At any one spot over the ocean, the rate at which water evaporates is a function of

  • The surface temperature of the water,
  • The surface temperature of the air,
  • The humidity content of the air, and
  • Surface winds.

Evaporation rate increases with increased air and water surface temperature, decreases as the relative humidity increases. Very calm air results in a thin layer of fully saturated air just above the water. This thin layer diffuses into the atmosphere as a whole. Diffusion is a slow process. A slight wind significantly increases transport from that surface layer. An even stronger wind keeps that surface layer from forming.

Integrating this local evaporation rate over all the waters of the Earth results in a global evaporation rate. Global warming on average increases both air and water temperatures, thereby increasing the evaporation rate.

Melting of the ice sheets does result in sea level rise, which in turn increases the surface area of the oceans, which in turn increases the global evaporation rate. This is a rather small effect compared to that of global warming. The sea level rise at any point in time is rather small. It only becomes significant on multi-decadal time scales. Moreover, even a two meter rise in sea level won't increase the surface area of the oceans by that much. Melting of all of the ice over Greenland and Antarctica most certainly would, but that won't be a problem for many hundreds of years. The immediate problem is what happens over the next 85 years or so, to the end of this century.

Improve this answer
$\endgroup$
9
  • $\begingroup$ Nice answer. In regard to the OP's assertion that "there is a tremendous amount of extra water vapor in the atmosphere", it would be really cool to add some back-of-the-envelope calculations to this answer. $\endgroup$
    – naught101
    Sep 8, 2014 at 13:40
  • $\begingroup$ @naught101 net evaporative flux from the ocean is a function of the SST, salinity and the local air temperature above the surface. The only real contribution mass melting will have is increasing surface area of the oceans (v small rate with sea level rise) which I would put as negligible. $\endgroup$
    – casey
    Sep 9, 2014 at 0:00
  • 1
    $\begingroup$ Hardly any, if any at all. The immediate impact of increased melting might well be to reduce evaporation. That influx of cold fresh water will form a layer atop the sea water because fresh water is less dense than salt water. That will cool the air above, reducing evaporation. $\endgroup$
    – David Hammen
    Sep 10, 2014 at 5:39
  • 1
    $\begingroup$ @user128932 - It's not millions of extra tons. It's about half a trillion extra tons every year. All of that extra water accounts for about half of the sea level rise. The other half results from the fact that water expands as it gets warmer, and the oceans as a whole are getting warmer. $\endgroup$
    – David Hammen
    Sep 12, 2014 at 13:01
  • 2
    $\begingroup$ @user128932 - The atmosphere is not getting appreciably "thicker." We humans have merely increased the amount of some trace gases, namely carbon dioxide and methane. This has made the atmosphere thicker by about 0.01 percent. Those trace gases do however have a rather significant impact on temperature. $\endgroup$
    – David Hammen
    Sep 15, 2014 at 11:52
2
$\begingroup$

To the contrary that's how many people explain the historical rain & snowfall events around the world. As the poles melt more water is absorbed into the atmosphere, concentrated in the jet streams and eventually dumped thousands of miles away.

Improve this answer
$\endgroup$
1
  • $\begingroup$ So water vapor from the melting poles and sublimation (maybe) are absorbed into the atmosphere and heat mixed with the water vapor powers a lot of rain and storms dumped thousands of miles away , not in my backyard. $\endgroup$
    – user128932
    Sep 10, 2014 at 5:36

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.