greenhouse gases are transparent to visible light, but absorb thermal infra-red and warm up. they then emit infra-red themselves - half towards space, where it was going in the first place, but half back down to the ground. The overall effect is like someone wearing a jacket on a sunny day - or of course a greenhouse with glass walls.
First, one has to define climate change. The climate is always changing and any change made to the environment will have an affect on the climate. That affect may not be measurable, but it will have an affect.
Adding CO2 to the atmosphere (or any GHG) will have the affect of raising the temperature slightly. The affect is unknown. We know that doubling the CO2 accounting for CO2 alone will have the affect of increasing the temperature by about 1 degree celsius. What we do not know is the amount of positive or negative feedbacks that influence the system. A positive feedback would increase the affect from say 1 degree to 2 degrees. A negative feedback would decrease the affect from say 1 degree to 0.5 degrees.
The amount of feedbacks is currently nearly a wild guess. That is to say that it is a guess based upon paleoclimate data. An example of paleoclimate data is using the thickness of tree rings to find the temperature in the past. They then determine the CO2 concentration in the past with another measure, say ice core data. Then they use other measures to try to determine other factors that may be involved. Then they try to model the temperature in the past using those factors. Then they use the model developed to try to figure out what the feedback effect is. Knowing the process, it becomes easy to see why I compare this to a guess.
Upon using the model to develop the feedbacks, they create a new model based upon recent, more accurately measured data for where we are. They then guess at what the future CO2 concentration is going to be, what the other factors are going to be, account for the feedback and voila they have a guess at the future.
Even the curent temp are not really an average global temperature. For this, they take measurements at a bunch of sites over differing times using differing standards. They "correct" the data and standardize the data. Then they run another model to spatially model that average temperature of the world.
So you are dealing with a model made from models with factors from other models using data ranging from the thickness of trees to actual temperature measurements. This is the uncertainty inherent in the process.
So this certainly affects the climate, but how? For this, they look at individual factors like tornadoes and make another model of how that factor was affected in the past and models it in the future using the temperature model to direct the temperature input in the model they made using the data from the past modeling.
So my answer is NO ONE KNOWS. The modeling process itself has too many sources of error and uncertainty to make any claims at all. IF AND ONLY IF the models show accuracy in their predictions, I will accept them as worthy of proper consideration. Otherwise they really stand as the first part of the scientific method where you develop a hypothesis based upon observations.
start at NASA
http://climate.nasa.gov/key_indicators
http://www.rkm.com.au/ANIMATIONS/carbon-... <== here's the physics.
http://upload.wikimedia.org/wikipedia/co... <== Note that CO2 intercepts a different wavelength than water. In addition, as CO2 warms the oceans, more water evaporates, increasing it's effectiveness.
All non solids separate in the upper atmosphere. This is how nature protects our plant. Mike
define climate
