Are Humans the Cause of Global Warming?
As mentioned in What is the Greenhouse Effect? our atmosphere is made up of many different gasses all of which contribute in different amounts to the heating of the earth. Behind water vapour Carbon Dioxide (CO2) is the next most effective gas in global warming, causing around a third as much warming as water vapour. Methane is next behind carbon dioxide.
Unfortunately, due to human habitation the concentration of gasses in our atmosphere has been changing. The amount of CO2 in our atmosphere has steadily increased since the start of the industrial revolution when humans began burning fossil fuels in earnest. Methane has also risen, even more dramatically that CO2, but it remains less concentrated as the initial amount of methane in the atmosphere was much smaller than that of CO2. The correlation between rising levels of CO2 and methane and rising industrial activity on earth is quite easily seen and had led many scientists to state categorically that humans are indeed contributing to global warming.
This is further backed up by the fact that scientists can look far into the past to see what gasses were present in our atmosphere at that time. This is done by examining ice deep under the arctic as when that ice was formed it stored the gasses that were present in theatmosphere at the time. By taking a long thin ice core from the surface we can see a history of the earth's atmosphere. From this we have discovered that the concentrations of CO2 and methane in the atmosphere are currently the highest they have been for at least 650,000 years, and in fact using geological evidence it looks like the last time they were as high was around 20 million years ago.
