I disagreed with it for awhile because of the silly arguments I'd here from people, mainly put forth in a political context. But someone who was scientifically knowledgeable about it explained that carbon dioxide absorbs more radiation (or kinetic energy/heat) from the sun over oxygen and reflects it back to the Earth. This is a problem because as we increase the concentration of carbon dioxide in the atmosphere, the temperature of the planet is increasing at a much faster rate compared to history; we could end up with unsustainable ecosystems.
This ^ but...
Different matter absorbs different frequencies of light. CO2 will absorb IR waves and make heat. The ground absorbs a portion of regular light that CO2 does not absorb and then has extra energy to emit IR back away from the earth. CO2 absorbs that light as it tries to leave producing heat near the earths crust heating our lower atmosphere.
Hopefully that makes sense so far.
The argument against this is that the increased CO2 exists evenly throughout the atmosphere and the IR coming from the sun will absorb nearer the top of the atmosphere away from the crust allowing the heat to dissipate into the outer atmosphere more readily. With the increased CO2 much of the IR from the Sun never reaches the earths crust to heat it thereby compensating for the heating affect of the of what I described in my first paragraph.
But how much IR is the sun really emitting? Near 50% of its energy is in IR but CO2 only absorbs a narrow band of IR.
[BIMG]http://en.wikipedia.org/wiki/Sunlight#mediaviewer/File:Solar_spectrum_en.svg[/BIMG]
So now we have to determine exact measurements to determine who is right so we look at the global temperature budget.
[BIMG]http://en.wikipedia.org/wiki/Earth's_energy_budget#mediaviewer/File:The-NASA-Earth%27s-Energy-Budget-Poster-Radiant-Energy-System-satellite-infrared-radiation-fluxes.jpg[/BIMG]
Now we are speculating but the earth is absorbing 163.3WM2 that could potentially be a heating of the earths crust but is also absorbing 169.9WM2 of IR before it gets to the crust and dissipating it in space.
*************
look at that sunlight spectrum chart and look at the areas that say H20 vs the little spot that says CO2. Notice the yellow being the unabsorbed energy and the red being what is left. Nearly all the energy is absorbed by H20 and almost none is absorbed by CO2.
The argument against Global Warming is often that H20 is the main contributor to the green house affect and the CO2 will barely be registerable in comparison.
The coutner to that, as it is stated by some, that because CO2 is increasing the temperature the H20 in the atmosphere will increase causing a further increased green house effect. Increased temperatures cause the water to evaperate into the atmosphere.
The counter to that is that H20 is already absorbing all the energy it can and it is also the only thing transfering energy from the oceans to the upper atmospher and causing cloud cover to cool the earth therefore the H20 will reduce the effect of global warming that might occur by CO2 increases.
Another interesting thing is that we have less than 1% CO2 in the atmosphere.
CONCLUSION:
Green House Gases are not going to be world ending but even small degrees of temperature can cause ice to melt on land which goes into the ocean and causes the oceans to rise. This will be bad for our coastlines.
The bigger and more serious issue is the plankton that is dying because of the increased CO2 in the oceans that is acidifying the oceans. Plankton is a major source of food for the fish in the oceans and also producing a large part of the worlds oxygen.
