Thread: science (global warming)

hey people, how you doing? I am new to all this topic so please bear with me. Ihave just started a degree in biology and im struggling with the global warming chapter, which unfortunately is the first book. To be honest i think i have jumped into the deep end, having no scientific expierence. Can anyone help?

There are a few trained scientists on these boards (I am not one) that would be more than willing to help. Do you have any specific questions?

thankyou for your interest the only question i really have is: Consider a molecule of water that is in a gaseous state (i.e. water vapour) in the atmosphere above an ocean.What possible route around the water cycle by which the water molecule could complete a whole cycle,, and to include the prosesses involed in the description. (Assume that the molecule comes into contact with land and the ocean before ending up back in the atmosphere.) I just dont understand

There is a contradiction in terminus in the title of this thread. Global warming versus science. Global warming is no science. Science is falsifiable, global warming isn't falsifialble. No matter, how long global temperatures will continue to cool, it will always be global warming. Hence global warming can't be science. it's just politics and ideology.

Anyway, that water molecule, it's the air conditioner of the world. Remember that it takes about 2.5 kilojoule for a gram water to evaporate from the ocean surface. And only the sun is providing those kilojoules.

Then in the processes of convection of warmed air, the molecule rises in a parcel of air, as the pressure decreases, this parcel expands and cools by that adiabatically. This means that the water molecule get sluggish and several water molecules start to cling together, the water condensates, at higher altitudes, forming clouds but also releasing that latent heat again. So that cloud is a lot warmer than it would be without the tremendous heat transport from evaporation and condensation.

Now getting the favorite radiation idea of the alarmists, this cloud is the main emitting source of the heat/energy in the infrared frequency ranges. But it also emits high above the Earth surface in random directions and therefore the chance that an energy parcel (photon) hits the earth, rather than escapes into space is inverted proportional to the ratio of the optical depth above and below that cloud.

So the higher the cloud, the more energy it emits to space. And if for whatever reason the earth surface was to warm up, it has two effects, it would increase the evaporation rate needing more kilojoules and it would tend to send the clouds to higher elevations, radiating to space more effectively. That's how Earths air conditioner works, a gigantic negative feedback system, which does not allow for global warming scare.

Anyway, following that molecule, it is now in a snowflake or raindrop at the ambient temperature, falling down and warming up in the warming atmosphere, but this warming lags and the drop hits the surface at a slightly lower temperature than the environment, cooling it even a little more. But remember, in the end it carried away a tremendous amount of energy, 2500 joule per gram to be emitted from higher altitudes into space while the rain did not bring this energy back.

Trigger. As Kalster suggested there are several trained scientist on these forums, my own graduate education in atmospheric science. As an open forum though, I suggest to take things posted here with a grain of salt.

For example from the previous post:
"So the higher the cloud, the more energy it emits to space. And..."
This is almost always wrong. Clouds, unless they sit on top of a deep inversion (usual) are colder and emit less IR radiation than the surface or clouds below them. Convective clouds tops, as used in the same post are think and particularly cold, and emit much lower IR radiation than the surface would in under a clear sky. In this way clouds create their own surface warming effect. This is nothing you don't already know from everyday experience--clear nights get colder than cloudy ones.


As for your particular question, wiki has a pretty good write up on water cycle, that better than something I could do off the cuff.
http://en.wikipedia.org/wiki/Water_cycle

I'd be happy to answer particular details though--there are entire fields of science such as cloud physics that can get deeper than most forum member would ever care to get into...LOL.

Welcome to the forums.

To your specific point about individual water molecules, if you followed a single molecule it might complete the cycle in a few weeks, or it might take a thousand years, depending on the path it takes. It could evaporate almost immediately after hitting the ground, or it might be drawn into a tree and photosynthesized into sugar, or it might find its way into an aquifer and stay there for many years. Meanwhile other molecules might flow out of that aquifer, or be released by a burning or decaying tree.

While the overall mass balance stays somewhat constant (as long as the average temperature is constant) the individual molecules returning to the top of the cycle are not necessarily the same ones that started there a few weeks ago.

I don't know if this was the source of your confusion, but I hope it helps. I can remember as an undergrad being very frustrated at not understanding stuff that seems so obvious today.

Originally Posted by Bunbury

To your specific point about individual water molecules, if you followed a single molecule it might complete the cycle in a few weeks, or it might take a thousand years, depending on the path it takes.

Excellent point. On average a water vapor molecule spent about ten days in the atmosphere--of course there being a wide range from seconds to a couple months.