Global warming is caused by the build up of greenhouse gasses, for example co2. They trap the sunlight, and prevent it from reflecting back into space, therefore we get hotter. Well, thats the basics.
With ozone, its a different matter. cfc's (chlora flora carbons) break down ozone. Cfc's are found in aerosoles and some fridges and freezers. Because ozone is made of oxygen (made up of 3 oxygen particles) the cfc's break it down into normat oxygen (2 particles) and just a single particle, which will then join with another single. So ozone is changed into oxygen, thats why its getting thinner.
Its always been happening, but due to the rapid removal of trees hundreds of years ago the carbon emissions are hard to control. (because trees convert carbon back to oxygen). People think carbon is bad, but its needed, there is just an imbalance these days.
Biggest causes are cars (especialy large engines), combustion of fossil fules (coal, oil), and cows! Due to their farting which is high in methane.
Too be honest, the biggest causes are the less economicaly developed countries that are coming up too their industrial revolution that are causing the most damage. Because their main industry is manufacturing so they use fossil fules solots of carbon dioxide, their cars have less rules so worse fuel (leaded!
) no catolitic convertors and no mot's or tests to keep emissions low. Also they cannot afford the technology that is better for the environment (nuclear power stations are cheaper and more efficient than solar pannels for example).
If we all used renewable energy sources, or decent fuels then we would not have these problems. For example BP's new fuel, ultimate claims if every car in the uk uses their fuel, it would be equivilent to taking 1 million cars off the road. Reforestation is also needed.
There are worldwide agreements that have been set up to control emissions, the main one being the kyoto agreement. Thats where each country has a quota (limit of emissions the country can output) with fines being placed to countrys failing to follow the rules. Not taking a stab at the USA here, but they did not sigh this agreement. Thats not taking responsibility for their actions. I personaly feel they should be forced to sign.