# Tag Info

## Hot answers tagged water-vapour

40

Your question about water vapour is quite a common one among people learning about the greenhouse effect. Once you discover the relevant proportions of water vapour and CO2 in the atmosphere, it's perhaps natural to assume that the CO2 can't be playing a major role. In reality it doesn't work like this, for at least a couple of reasons. First, let's look at ...

14

What's actually happening is scattering of light, both off of aerosol particles and nitrogen and oxygen molecules. For a review of quantitative models of light pollution as a function of distance from cities see Light Pollution Modeling . Some consider height as well as distance. To get a rough estimate of what size of lights-out event would be needed ...

13

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 ...

13

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,...

11

Experiments don't necessarily prove things, per se; and in particular, a single experiment tends not to prove anything - at the very least, replication of the experiment is required. Experiments provide contributory evidence. Confidence in a hypothesis can come about from a combination of theory, lab experiments and natural experiments. Our knowledge about ...

10

Leaves, mostly. Photosynthesis requires carbon dioxide, and it gets it via stomata - small controllable pores in the leaf. When the stomata open, water goes out, because the air is generally drier than the interior of the leaf. Water in the leaves is drawn up from the roots, via the xylem, using the suction from the lost water in the leaves, and also acting ...

7

To see why we can't perform an experiment in lab conditions to verify the greenhouse effect, we need to start by considering how the [rather badly named] greenhouse effect operates: The Earth is in (to all intents and purposes) a vacuum, so it can only gain or lose heat via radiation. The sun emits most of its radiation at visible and UV wavelengths. The ...

7

Without water in the air, clouds cannot form and evaporate quickly if they do and so a sudden drop in evapotranspiration that resulted in low humidity could decrease the prevalence of rain. But, in simulations, there's not usually much of a measurable effect (http://www.sciencedirect.com/science/article/pii/0273117787902900?np=y). This is because there's a ...

7

The short answer to your question really is just this: Yes, CO2 causes global warming. There are many resources out there on the internet that explain this in about as much detail as you can tolerate, and whatever we could answer here does not come close to what others have already collected. I would suggest you start at the wikipedia page on global warming ...

6

The formation of dew is due to atmospheric moisture and temperature. Given that dew forms on all sides of your car at your mother's house, this makes me think the car is more exposed at you mother's house so that the car is uniformly cold and the temperature of the car is at, or below, the dew point. With dew only forming on one side of the car when at ...

6

The Faint Young Sun Paradox - how greenhouse gases can keep a planet warm: When the Earth formed 4.5 billion years ago the Sun was around 30% less luminous than it is today and it has increased steadily since, based on well established models of solar evolution. Simple energy balance models of the Earth show that, with a similar atmosphere to today, the ...

6

The formula for moisture flux is $$q\vec{V}$$ where $q$ is the water vapor mixing ratio, which can be found using mixhum_ptr and $\vec{V}$ is the velocity. Therefore the divergence of the moisture flux must be $$\nabla{\dot{}q\vec{V}}=\frac{\partial(qu)}{\partial x}+\frac{\partial(qv)}{\partial y}+\frac{\partial(qw)}{\partial z}$$ \approx\frac{\delta(...

5

Negative values for the ET, both potential and actual, usually refer to condensation. See also "ERA5 mean evaporation rates data - Why is that negative?" Regarding the ability of the physically-based hydrological models to handle condensation, I'd say that it's difficult to give you a general answer: it will depend on the specific math behind the ...

4

The linked article talks about irrigated agriculture so I'll focus on that, but things are generally the same for rain-fed agriculture, except you have less control on the water application and there is no loss in getting the rain to where it hits the ground (yes some rain evaporates as it falls but we measure rain at the ground). For irrigation water, ...

4

The water cycle isn't geology, but it's important to pedology, which is an earth science. Agricultural water can be converted (by photosynthesis) directly into simple carbohydrates that we eat; or converted into carbs and then used as structure or energy that keeps the organism alive and growing, but isn't the mass we finally eat; or used to build more ...

3

Someone (Casey?) can probably provide a fuller answer, but the basic idea is that ice molecules are kind of locked into place by the molecular structure of the ice crystal, and can't vibrate very much. Increase the energy, and the molecules vibrate more until the molecular attraction is disrupted to become water, when they vibrate a lot. Increase the energy ...

2

There isn't much to choose between them. They are both variants of the same general equation. They both take account of the three main variables: temperature, rate of advective removal of moisture (proportional to surface wind velocity), and difference in vapour pressure (which can be related to humidity). In countries using SI units there are several other ...

2

The atmosphere is continuously mixed by turbulence, so no sorting of its ordinary components can occur easily and rapidly. Twice a day change, anyway, is far too fast for anything but some tidal effect on pressure and thus on temperature. Ok, these might indirectly slightly modify some thresholds and balance e.g. between states change (water) and some ...

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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.

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See this answer. Actually already snows on Mars. The snow, made of carbon dioxide, has been observed and studied by orbiting spacecraft. Aside from the different chemical composition from the stuff we shovel on Earth, Martian $\text{CO}_2$ snow also is very finely divided, microscopic in size in fact; likely this is related to the low density of available ...

2

For a study relating to rainfall, I would be inclined to look at total column water vapour (TCWV), also known as integrated water vapour (IWV) or precipitable water. They're all (more or less) the same thing. The company Remote Sensing Systems describes it as: Total column water vapor is a measure of the total gaseous water contained in a vertical ...

2

While the effect might be measurable (just barely) it's small. We add about 30 billion tons of CO2 to the air every year. About half of that gets absorbed into the oceans (give or take), the remaining 15 billion tons remains in the atmosphere for a long time. 280 PPM CO2 the post ice-age, pre industrial revolution number works out to about 1,000 ...

2

I can identify two parts of how this may be confusing. The first is vapor pressure with respect to ice, and the second is supersaturation. First, let's look over the equation for phase transitions. The saturation vapor pressure can be described by the Clausius Clapeyeron equation. Solving that equation explicitly (i.e. not using Bolton's formula used in the ...

2

The saturation vapour pressure defined by the American Meteorological Society: The vapor pressure of a system, at a given temperature, for which the vapor of a substance is in equilibrium with a plane surface of that substance's pure liquid or solid phase; that is, the vapor pressure of a system that has attained saturation but not supersaturation. The ...

1

I think your ~2 figure for CO2 greenhouse amplification is in error. * In the last 200 years it's gone from the high 280s to low 400s. This is an increase of about 50% Good thing it's not linear as the previous greenhouse effect is overall about 18K. If there was no effect, the earth would average about 0 C. * As CO2 increases it takes more bounces for ...

1

The long term influences upon the Earth's atmosphere are additions, subtractions and internal variations. The additions consist of gravitational attraction of passing gas molecules from space, which is insignificant, and outgassing from the solid Earth. The latter is 'new' helium from radioactive processes, and volcanic gasses which are mostly long-term ...

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