What is the scientific basis for anthropogenic global warming?

Global warming is the rise in average temperature of the Earth. Scientist agree that this continuing rise in average temperature is due to the the increase of greenhouse gases. As the concentration of greenhouse gases increase so does the average temperature of the Earth. Many would argue that this is not a problem and say that we are just going through a normal climate cycle. The data really seems to show otherwise.

Figure 1. Global Temperature Change Compared with CO2 Change. [1]

Shown from the data above that around the same time that carbon emissions increased so has the average global temperature. The greenhouse gases that seems to be the most harmful is carbon dioxide although methane is a close second. Most skeptics will point out the fact that most carbon dioxide production is produced by nature.

Figure 2. Global carbon cycle. Numbers represent flux of carbon dioxide in gigatons [2].

However from Figure 2 we can see that most of the CO2 produced by nature is also absorbed by nature. Therefore the CO2 produced by man is a big problem because the majority of it stays in the atmosphere. The CO2 produced by burning fossil fuels and land use seems minimal but about 40% of the approximate 29 gigatons of CO2 is absorbed by the atmosphere [2]. With the continual build up of greenhouse gases similar to CO2 caused by humans, the greenhouse affect becomes more apparent. As mentioned in a previous entry the greenhouse affect is caused by greenhouse gases being opaque to infrared heat. Therefore, the higher concentrations of greenhouse gases in the atmosphere the hotter the Earth will become. 


[1] http://www.google.com/imgres?q=average+earth+temperature+history&um=1&hl=en&sa=N&rlz=1C1CHKD_enUS410US410&biw=1366&bih=667&tbm=isch&tbnid=6PBS3WFHUDiKUM:&imgrefurl=http://techskeptic.blogspot.com/2007/04/techs-post-on-global-warming.html&docid=tmmS6EqVNUFaVM&w=480&h=766&ei=wdBjTpawFeeAsgKT1qGXCg&zoom=1&iact=rc&dur=247&page=2&tbnh=168&tbnw=106&start=15&ndsp=17&ved=1t:429,r:3,s:15&tx=26&ty=40
[2] http://www.skepticalscience.com/human-co2-smaller-than-natural-emissions.htm