Several points, I’ll take each in turn…
DESCRIBE THE GREENHOUSE EFFECT.
The mechanism by which heat is retained within the atmosphere.
WHAT ARE THE THERMODYNAMICS OF IT?
We receive heat energy from the Sun in the form of incoming solar radiation. Because the Sun is an exceptionally hot source the parcels of heat energy (photons) are in a high energetic state and have a short wavelength.
When the solar radiation reaches the atmosphere some of it is reflected back into space, some makes it’s way down to the surface of Earth. Lighter surfaces such as snow and ice reflect much of the energy back into space but the darker surfaces such as soil and water absorb it (the darker the surface the more heat is absorbed).
These surfaces that absorb the heat energy warm up, when the ambient temperature drops (e.g. night time) that absorbed energy is radiated back outward. This time it’s coming from a much cooler source, it’s less energetic and has a longer wavelength.
This re-radiated energy, thermal or infra-red radiation, has a wavelength that corresponds with the vibrational frequencies of greenhouse gas molecules and this allows the the greenhouse gases to absorb some of this heat energy.
Once again, the heat is re-radiated back out. The molecules release it in random directions and some is lost into space, some comes back down to Earth. It’s this returning heat that keeps the planet at a habitable temperature.
The increase in greenhouse gas concentrations means more heat is being retained within the atmosphere, this is what we refer to as global warming. The consequence of global warming is climate change.
HOW DOES IT RELATE TO THE STRUCTURE OF THE ATMOSPHERE?
The atmosphere has several distinct layers to it, there are transition layers (or pauses) between these layers. Each layer is identified by it’s characteristics and the differences between other layers.
Thermodynamic properties of each layer are very different. The layer nearest Earth is the troposphere, the higher you go in this layer the colder it becomes, above this layer is the stratosphere and the boundary between the two is the tropopause. As you ascend through the stratosphere it begins warming up again. Passing through the stratopause you reach the mesosphere where it again cools down.
There are further layers above this such as the ionopshere and exosphere, again there are temperature changes and the atmosphere (such as it is) behaves very differently as it’s in an ionic and plasma state.
The greenhouse effect and global warming exists primarily within the lowest layer – the troposphere. It’s here that most of the mass of the atmosphere is found.
As the greenhouse effect weakens or strengthens the amount of heat energy passing through it varies, this means that the stratosphere (the next layer up) responds by cooling or warming.
WHAT WOULD CAUSE A RUNAWAY GREENHOUSE EFFECT?
A runaway greenhouse effect is when one mechanism or a series of mechanisms come together in such a way that that the greenhouse effect runs out of control. This could be due to a failure of a cooling mechanism, the intensification of a warming mechanism or through a series of events that ultimately leads to uncontrolled warming.
Here on Earth one example would be when a warmer atmosphere causes the polar ice to melt, the melting of the ice reveals the darker water and land beneath it and this allows more heat to be absorbed. This heat is released into the atmosphere causing further warming, this results in more ice melting and so a coupled feedback is established.
This process has happened on Earth in the past but it’s limited by the fact that at some point all the ice melts and the feedback fails. The cause is the passage of the entire solar system through the dense spiral arms of the Milky Way galaxy. It’s a very slow process but the effect is extraordinary. It’s also something we don’t need to worry about for another 70 million years or so.
On Venus it’s a very different story. Here the atmosphere has gone into meltdown. Venus used to be very similar to Earth but millions of years ago the tectonic plates stopped moving, the mechanism by which carbon was pulled down into the planet stopped, the carbon oxidised to form carbon dioxide, this built up in the atmosphere causing more and more warming. Soon it got so hot that the seas and oceans boiled and became vapour, the solar wind stripped the planet of the vapour leaving only carbon dioxide behind. In time the greenhouse effect became so great that Venus is now the hottest place in the solar system other than the Sun itself.
IS THERE ANYTHING WE CAN DO TO STOP IT OR CAUSE IT TO INCREASE IN ACTIVITY?
The greenhouse effect is dictated by the presence of greenhouse gases in the atmosphere. Remove them and there’s no greenhouse effect, increase them and the effect becomes more pronounced.
Some greenhouse gases are better than others when it comes to retaining heat. The most abundant of all greenhouse gases (by a factor of 25) is water vapour, but as greenhouse gases go it’s very weak. There are other gases that are hundreds of thousands of times more powerful.
By increasing the amount of greenhouse gases in the atmosphere we can enhance the greenhouse effect and this in turn will lead to warming.
Similarly, we can reduce the amount of greenhouse gas in the atmosphere, this will reduce the amount of heat that can be retained and the planet will cool.
There are also gases that work in opposition to the greenhouse gases in that they block incoming heat from the Sun (as opposed to outgoing heat from Earth). If the amount of these gases change then the result is a change in the amount of solar radiation reaching Earth’s surface.
Many of these cooling gases are sulphates with sulphur dioxide (SO2) being the primary one. Our industries and power stations used to produce a lot of SO2 and this helped cool the planet down. Legislation now means that SO2 emissions have fallen so the cooling influence is weaker.
If we deliberately or inadvertently vary the concentrations of warming or cooling gases in the atmosphere we can influence the global temperature.
Co2 vibrates in reponse to certain frequencies of long wave radiation, and emits radiation of it's own, some which can return to earths surface, however the effect is very small and it is generally accepted that a doubling of CO2 (by about the year 2050) will cause 3.7watts per sq meter warming which is equal to 1 degree C.
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The so called runaway effect is that this small warming will cause a rise in water vapor (a stronger GHG) and this rise in water vapor will cause more temperature and so on, this is a ridiculous concept because any small warming would have this effect, not just from CO2 and as we have had lots of warming (and cooling) episodes in the past, and our climate has'nt spiralled out control, there is no reason to believe it can happen now or in the future.
In fact water vapor has negative (cooling) feedback reponses as well by transfer of earths heat by evaporation and condensation (the same way a refridgerater works) and of course cloud formation which shades earth from the sun rays.
Over Earths long history its climate has been incredibly stable, taking into account tectonic movements of continents, extreme volcanic activity, and huge changes in CO2 levels (some 20x times more than what we have now) it seems all the liquid water we have acts as a regulator and controls the maximum temperature earth can obtain, however it does'nt all ways work in the opposite direction, as when water gets tied up ice sheets it loses some of its ability to control, hence the ice ages.
Is there anything we can do to stop it, No I don't think so the climate mechanism is too strong for us to have much effect on it.
Jeff M. I tracked down that paper you quote from and it is not about runaway climate change it's about formation of our universe/solar sytem
These three ‘terrestrial’ planets were probably formed via accretion of the same or very similar chondritic material. The radically different outcomes among the three planets is probably due to their relative distances from the Sun as depicted in Figure 2.9, and to the fact that Mars is smaller than Earth and Venus.
Another quote from this paper
The figure suggests that atmospheric water on Venus was always in the vapor state leading to a pronounced greenhouse effect as degassing evolved. Only on Earth has degassing led to the simultaneous existence of all three phases of water. With 71% of its surface area covered with liquid water, Earth is truly unique.
Kano: A runaway greenhouse effect occurs when upper layers of atmosphere do not cool enough to the point of condensation of water vapour and the molecules of H2O rise to a point where dissociation occurs. Oceans literally evaporate away. When this occur there is no longer many CO2 sinks, the CO2 in the atmosphere rises and the warming attributable to that CO2 occurs. On Earth that will occur when the Sun reaches a point to warm the tropopause to a point near or above the condensation temperature of water vapour. Venus has a runaway greenhouse effect.
http://www.unc.edu/~rchristm/Water%20Vap...
Homework was invented for a reason. If you must resort to this half-anti-science site instead, at least ask one question at a time.
In my humble opinion if we use interaction between more than two echo machine.
Describe the greenhouse effect. What are the thermodynamics of it? How does it relate to the structure of the atmosphere? What would cause a runaway greenhouse effect? Is there anything we can do to stop it or cause it to increase in activity?
