Because there's only so much warming that can be caused by a given quantity of CO2.
The way it works is basically like this.
Incoming sunlight (mostly UV and visible light) passes right through CO2 without really interacting with it. Then, it hits the surface, and some of it is absorbed, and re-emitted as infrared light. CO2 *does* stop infrared light. So, a photon trying to leave Venus (or any planet with CO2 or other greenhouse gasses in its atmosphere) will be bounced around, a little like a pinball. Eventually, even with a very thick CO2 atmosphere, the photon will eventually escape, but the longer it spends bouncing around the atmosphere first, the warmer that atmosphere will get. The more CO2, the more the photon will bounce around before leaving (because it gets more and more likely that a given photon will, when emitted in a random direction, hit a molecule of CO2)
Imagine it a bit like this.
You're spraying water from a hose, towards a bucket sitting on sand. The sun is the hose, the bucket is the atmosphere.
If there's no bucket there at all (an airless world, like Mercury or the Moon), then the sand will get wet while you're spraying, but then the water will drain away when you're not spraying (the world will get fairly hot during the day and very cold at night).
If you have a small bucket (a world with a thin or CO2-poor atmosphere), you'll get some water in the bucket, and then the rest will just drain away. (the world will be warm during the day and cool at night, but not suffer the same extremes as an airless world)
The larger your bucket, the more water it will hold. And if you increase the size of the bucket, the water level will rise for a while. But, eventually, a given bucket will have all the water it can hold, and the water level will stop changing. Similarly, a given planet will get warmer if the CO2 level is changing (or has recently changed), but if the CO2 level isn't changing, the planet will reach an equilibrium temperature.
Spartan: Your answer is nonsensical. Many greenies on this site were saying 'traps' which is what the term greenhouse came from since the glass in the greenhouse traps the heat. But we know that the claim is that it absorbs an greater amount of heat than other gasses.
So it boils down to the same question that Buzzard asked. Meaning it keeps the heat from escaping back to outer space. Whether it absorbs it or traps it, it makes no difference as to the question.
Your side claims that when we would reach 0.04 percent CO2 we would get a runaway affect. We now know that isn't the magic number. But your side does claim that there is this runaway number. Venus would certainly prove that out. How come it hasn't run away like your cohorts are so enamored with scaring us? It is a good question. One which obviously you don't have an answer for so you side track the question and quibble with terms.
"If CO2 were NOT an efficient absorber of IR radiation, this would be spectacularly easy to demonstrate in laboratory. Funny how that doesn't happen." Now we get down to terminology again. It has been demonstrated that CO2 does block, stop or absorb some bands of radiation more efficiently than others. But it does not impede the whole infra spectrum evenly. Some heat radiation does escape the CO2 gassed atmosphere, in a wholesale manner. This has been PROVEN in many laboratory tests. That's a bit non sequiter.
So back to the original question, Venus has around 95% CO2. That should be far above the run away equivalent your side scares us with, 0.04%. How come, if that run away theory is correct, that hasn't happened to Venus?
Now go to Wikipedia
http://en.wikipedia.org/wiki/Atmosphere_...
and you will see in a graphical demonstration on the right hand side that Earth's CO2 level was once just as high as Venus'. The Earth should have burned to a crisp then, if your runaway theory is correct and Wikipedia is correct.
Buzzard's question is valid and as of yet not properly answered.
In direct answer to your question: That is a good question. Obviously no one here has a good answer. The only answer possible is that CO2 does not control the temperature. The true scientists on this site have been saying that for years now.
It is not a question of greenhouse gases, it's a question of atmospheric density.
Mars has 95% CO2, is farther than the sun, but once had liquid water in a time that our sun was supposedly less bright, Mars lost most of its atmosphere because it is smaller (less gravity) and it's volcanic era ended early.
Earth also had lost some of it's atmosphere but because it has more mass and more volcanic activity (spewing out gases) it was able to hang on onto enough atmosphere for life to remain viable.
Venus has huge mass and violent volcanic activity, and kept it's very dense atmosphere and that's why it is still so hot.
Mercury was too close to the sun and had its atmosphere blown away by solar wind.
Climate Realist. I am not talking about compression/temperature rise, I am talking about insulation, it's atmosphere is so dense it prevents heat escaping, and as you can tell by the constant 737K it even prevents heat entering.
Venus has a mean surface temp of 737°K.
Mercury has a mean surface temp of 200-340°K, despite being far closer to the Sun.
This is a function of heat trapped by Venus' atmosphere. I'm not sure why you think that if CO2 "traps heat" (it is known to be an efficient absorber of IR radiation) that Venus ought to melt or explode. That's a bit non sequiter.
If CO2 were NOT an efficient absorber of IR radiation, this would be spectacularly easy to demonstrate in laboratory. Funny how that doesn't happen.
Venus is made of rock. Put a rock under a blow torch and nothing will happen to the rock.
How much gravity did your rock have?
Kano
The density of Venus' atmosphere has nothing to do with its temperature. If it's atmosphere was ever compressed, it has had billions of years to cool down to its equilibrium temperature.
It's the carbon dioxide that's so dense that it prevents heat escaping.
Here on earth is air/ A THOUGHT on other planets maybe something else and rocks and boulders came from prehistoric poop. Mike
high temperatures re radiate the energy
