Global Warming: What is the Greenhouse effect? Can we PROVE it exists?

Question

OK Give me an Idiot's Guide Please

What is the Greenhouse Effect?

Can we scientifically PROVE that it exists?

Answer 1

I've sort of described the Greenhouse Effect in an answer to one of your other questions so apologies for any duplicity.

Greenhouse Effect is a not particularly accurate term that is frequently used to describe the manner in which Earth's atmosphere is being heated over and above it's natural level due to the heat retaining properties of certain gases in the atmosphere - the greenhouse gases.

The primary greenhouse gases, in order of their contribution to global warming, are water vapour, carbon dioxide, methane, nitrous oxide and dichlorodifluoromethane. There are hundreds of others, mainly synthetic, but between them they account for only a small amount of the greenhouse gases.

The gases have different residency periods or atmospheric lifespan. Water vapour for example remains in the atmosphere for 4 to 12 days, carbon dioxide for 115 years, sodium hexaflouride for 31,500 years.

The heat we receive from the Sun is able to pass through the atmosphere unimpeded by the greenhouse gases and that's because it's shortwave solar radiation. This heat is absorbed by the Earth and everything on it, when the ambient (air) temperature falls this stored heat is re-radiated back out as longwave thermal radiation.

The wavelength of thermal radiation (heat) is the same as the frequency of greenhouse gases and so the heat is able to be absorbed by the molecules of greenhouse gases. Subsequently it is re-emitted back out again, some goes up into space and some comes back down to Earth.

It's this additional burden of the downward transmission of absorbed thermal radiation that is the Greenhouse Effect.

As to whether it can be scientifically proved - yes it can and very easily. The notion was first hypothesized as far back as 1824, by 1893 it was an established and scientifically provable fact. It was largely through the work of a Swedish chemist, Svante Arrhenius, that the greenhouse effect and global warming became fact.

In a field or lab environment it can be measured and proven using sophisticated scientific equipment but it can also be proven in your own home. To do this all you need to do is fill a bottle with a greenhouse gas (methane from a stove, carbon dioxide given off as the bubbles from sodium bicarbonate (baking soda) or indigestion tablets). Put a thermometer in the bottle and another thermometer into a bottle of air, put the caps back on and place the two bottles in the Sun. The one with the greenhouse gas in will warm up quicker and retain the heat for longer. It's a small and simple experiment but it replicates what happens in the larger atmosphere.

Answer 2

There are a couple of answers to your question that are germane.

The first is that the equilibrium temperature of a body in space is governed by the Stefan-Boltzmann law. There is a term in this law identified normally with the Greek letter epsilon called the emissivity. This emissivity factor identifies how much incident radiation a body will absorb as well as how much it will radiate at a particular temperature. The greenhouse effect theory proposes that the constituents of the atmosphere around a planet alters the planet's emissivity factor.

The second reference below provides the equilibrium temperature of a planet warmed by a star. It makes an assumption that both the star and the planet have an emissivity of 1, i.e., that both are perfect black bodies. If this assumption were true, then the equilibrium mean temperature of the planet would never change. However, if either the emissivity of the star or the planet changes, then the equilibrium temperature will change.

The ratio of the star's emissivity to the planet's emissivity is the important factor for this effect. If the star's emissivity rises, then that ratio will increase and the planet will warm. If the planets emissivity rises, then the planet's equilibrium temperature will fall.

Your question asks if the greenhouse effect can be "proven". The answer is yes. It is possible to measure the mean emissivity of a planet, although it is not trivial since it requires a fairly lengthy measurement. However, one needs to eliminate emissivity changes due to cloud cover and surface "color" changes (oil slicks, plankton blooms, large burned areas, etc.) in order to extract the change due to atmospheric constituency.

Of perhaps greater importance is the question "can we scientifically prove that accessible changes in atmospheric carbon dioxide levels affect the temperature of the earth?" The answer to this question is also "yes". In fact, it is much easier to do this.

The Vostok ice core data (see reference) shows an extended history of the temperature and atmospheric concentration of carbon dioxide for the earth. In this extended (450,000 year) historical record, there has never been an incidence where carbon dioxide levels have changed before a change in planetary temperatures. That is temperatures rise before CO2 levels rise and temperatures fall before CO2 levels fall.

So, the Vostok ice core data provides sufficient information to show that accessible levels of atmospheric CO2 concentration has essentially no effect on earth's emissivity. That is, essentially no greenhouse effect can be attributed to atmospheric CO2 concentration.

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I find it necessary to amend this to address the post by Thomas K below. His post is accurate, but somewhat misleading. If the specific heat of the atmosphere was all that was in play, then the temperature of the planet would increase to infinity. That is, the radiant energy flux from the sun is ongoing, and the specific heat of the planet would simply convert that to heat. The Stefan-Boltzmann law is the controlling factor for the temperature of the planet. Not the specific heat of the planet's constituents.

Oh, no. More eye glazing ahead. Thomas K detected a debate, but really his response is more of a clarification as was mine. I would label it more of a conversation than a debate.

Thomas K correctly identifies ice or snow covered ground as key components in regulating the emissivity of the earth. My abreviated list of oil slicks and plankton blooms implied but could have specifically stated snow and ice effects. Anyway, the original question centered on the Greenhouse effect, which is purely atmospheric and my answer still stands. The Greenhouse effect can be measured, albeit with some difficulty, and accessible atmospheric carbon dioxide concentration has no associated Greenhouse effect. The loss of ice and snow may very well be a "bad thing", as Thomas K puts it, but since the only proposed intervention is to regulate CO2 levels, which have no associated Greenhouse effect, there is nothing we can do about the situation except prepare for the effects.

Answer 3

Greenhouse effect is caused by the reflection of heat back to earth as it tries to radiate into space. This occurs due to the infraction index of certain gases in the atmospere.

This is a proven effect. Look at Venus, a planet that should be fairly warm if it had our atmosphere. But it has an atmosphere with lots of CO2 so its average temperature is 872F (And will melt lead)

The only question is how much CO2 does it take to have a devastating effect. Let's hope we don't find the answer the hard way.

Answer 4

The greenhouse effect is easily demonstrated and proved in the lab.

The greenhouse effect states that there are compounds that act as a heat sink, that is, they absorb and hold onto heat, raising the ambient temperature.

Our atmosphere is about 80% nitrogen. Nitrogen has a specific heat (Cp) at 300K (about room temp) of 1042J/KgK. That means that it takes that much energy to raise 1 Kg of Nitrogen 1 degree C.

Under the same conditions, oxygen has Cp is 918J/KgK.

CO2 is 846J/KgK.

That means that it takes less energy to raise the temperature of CO2, as compared to the other gases in the atmosphere.

So, lets do the math, but keep it simple. You have 3 vials of the above gases in pure state and all at 300K (27C). You subject each one to 1042 Joules of energy. Here's the results:

Nitrogen raises 1 degree to 28C
Oxygen raises 1.14 degrees to 28.14
CO2 raises 1.23 degrees to 28.23.

The above is not theory - any reference book contains these numbers. Raising CO2 levels in the air raises the temperature - it's that simple.

Throw in water vapor, another greenhouse gas, to hold onto the heat (everyone has experienced the effects of humid days, or the difference between a sauna and a steam room), and you the greenhouse effect.

No theory - pure empirical science that I learned in 8th grade.

There are additional points to make, but I can already feel your eyes glazing over, so I'll stop here.

Update for Dr T.

Ahh, a debate! Prepare, ye newbies, for eye glazing.

Let's bring in 1 more factor. As Dr T mentions, let's bring in black body radiation.

Anyone who is involved in winter sports understands what snow blindness is about - the glare off the snow is enough to cause real damage to the human body. (If you're body does not block the radiation, it continues on away from the earth). The snow radiates much energy away.

If you stand on the same mountain in the summer, the danger has past - the earth now is absorbing more radiation. This is a quick and simplistic view of black body absorption.

As Dt T points out, there must be a regulating factor or the earth would continue heating up. That factor is called the seasons!

Now, lets start melting the polar ice cap during the summer, with the increased summer temperatures. We have now converted the artic ice cap from a radiating body to a black body. Rather than radiate sunlight back into space, the water absorbs more energy, adding to the melt rate. That's pretty much what the photographic evidence points out.

The moderating influence of the polar ice caps is disappearing - there can be no debate on that. I think that is a bad thing.

Dr. T's conclusion that no ice age is linked with CO2 levels is interesting. I have not reviewed the data, however, just because an event has not happened does not preclude it FROM happening.

As I pointed out in a previous question, there are many variables to this question - most have probably not even been identified. If we act like GW is real, the worst that can happen is we end up with lower energy bills. If we act like GW is NOT real, the worst that can happen is all of those dire predictions we hear about.

Further "amendments"

Dr. T, I enjoy our conversation! - more importantly, I think anyone persistant enough to read through this far is going away with useful info.

I respectfully disagree that you can seperate atmospheric warming (greenhouse) with rising ocean temperatures and disappearing ice caps - to me, they go hand in glove. As temperatures rise, ice melts. This past summer, the artic recorded temperatures well above normal - 22c! Not surprisingly, the loss of ice mass was also one of the largest on record. Loss of ice results in higher ocean temperatures (less radiation losses) which leads to higher melts, and so on.

As I mentioned in my first response, there are many variables to this beyond the specific heat of CO2. This is a chain reaction, one event enabling another.

Answer 5

The scientific proof for the green house effect is that it is more then 0 degrees C on the planet. With out the green house effect our planet couldn't sustain life because the planet would be to cold.

Answer 6

Yes. Have you ever been in a greenhouse? Global warming is a fact. The only thing is we are not 100% sure what is causing it.

Answer 7

Yes. Have you ever been in a greenhouse? Global warming is a fact. The only thing is we are not 100% sure what is causeing it.

Answer 8

The average centigrade temperature have believed improved by 2 during the latest century,because of the increase of CO2.

Answer 9

Its nothing but the world full of CO2. It means due to the excess of CO2,the green things such as plants, trees gets destroyed.(Even trees & plants need oxygen to respire). Yes, we can prove. See, our earth's temperature is increasing day by day.It is due to CO2. Because CO2 traps the heat and thus helps to increase the surface temperature. It is mainly caused by the factories, vehicles, etc...

Answer 10

Over the last 60yrs or so governments have worked on weather changing. Knowing this like cloud seeding is it that their is no natural climate changes . Just government controlled weather changes.