Since I got asked again and again, whether or not I believe in climatic change, I feel about posting a final clarifying statement on that issue. I did not become a scientist to make my decisions on the ground of obscure conveniences but on the bases of provable facts.
One of those facts is, that carbon dioxide lets pass electromagnetic waves of a wavelength below 1 µm almost unaffected but absorbs infrared light quite well. A similar behavior is known e.g. for water steam (extensive absorption over ~0.7 µm). (Consult your physics book for details and other gases.)
Therefore a ray of short wavelength sunlight may easily pass the earth’s atmosphere and reach the solid ground. There it gets absorbed and is re-emitted as light with a higher wavelength (due to the second law of thermodynamics). This infrared ray now has serious troubles leaving the atmosphere right away because it gets absorbed by the green house gases. This effect is well known as the “green house effect” for ages and is probably also responsible for the wonderful taste of your grandma’s paprika.
It’s quite obvious, that the magnitude of this effect is related to the atmospheric concentration of green house gases. At total absence of those gases, our sweet planet would be a rather rough place with an average temperature of about 254 K (-19 °C) .
So far we didn’t discuss anything very thrilling. However, we have seen that increasing the concentration of green house gases will have an influence on the green house effect. The interesting thing is now, how that effect looks like.
This question is difficult to answer because there is a huge range of sub effects that are started by changing one parameter. (Just for example: Assume we increase the CO2 concentration which, assume, increases the global temperature. This (warmer climate and more CO2) will make plants grow faster which so fore will store more carbon dioxide in biomass so the concentration might go down again, except…)
Scientists carried out several simulations based on different models that showed an increase of the global average temperature from 1.1 to 6.4 K within the 21th century . Even though, the results differ quite a lot, they show the general trend that the influence of artificially produced green house gases is probably not negligible.
One can and should of course criticizes those simulations. More research should be (and is) done on this topic and better simulations might show better or even completely different results. As far as we are, the mentioned results are all we have.
If you want to try out a new way of explaining the global climate and have good ideas for doing so or if you’ve found errors in today’s simulations, I will be glad to have an interesting discussion with you about. But if you simply want to discuss the issue in the way of standing up and claiming: “But I don’t believe it!”, I’d kindly ask you to do so with your vicar instead of me. He’s the expert on the field of belief and you will probably spend a very nice afternoon with him.
 Intergovernmental Panel on Climate Change Fourth Assessment Report. Chapter 1: Historical overview of climate change science page 97 (Download)
 IPCC (2007). “Summary for Policymakers”. Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. (Download)