An Inconvenient Truth- Fact #3

Fact 3: When Earth is on its axis and faces the Sun (summer), CO2 levels rise (= increasing global warming b/c CO2 traps the Sun's rays in the atmosphere), and when if faces away from the sun (winter), CO2 levels drop.
Source 1: http://en.allexperts.com/q/Astronomy-1360/earths-axis-global-warming.htm This source is by Philip Stahl. I'm not really sure how credible it is because it says he has experience in science, but only a degree in physics. Stahl says that there is no evidence that Earth's axis plays any role in global warming; it's all due to "man-made greenhouse gases". *This source goes against Fact 3. I personally don't agree with the source because it's not very credible and I believe that global warming is affected by both man-made gases and the CO2 levels that trap the Sun's rays (due to Earth's tilted axis).
Source 2: http://books.google.com/books?id=s2lkQiXo3pMC&pg=PA117&lpg=PA117&dq=CO2+levels+%2B+Earth's+axis&source=bl&ots=ZLRiwLs5-n&sig=fLvLbIC-sMPIicjSUFrhGl81iyU&hl=en&ei=2HPmSdKBOeT8nQe_l4SUBw&sa=X&oi=book_result&ct=result&resnum=2#PPP1,M1
This source is a book by Thomas L. Friedman, an expert on political science and I think it is a credible source. The source says that Earth has a lot of Co2 in its atmosphere. It also says thatover long periods of time, the Earth's tilt changes about two degrees which increases or decreases the sun radiation in different places according to seasons. *This source agrees with Fact 3. I agree with the source because increase or decrease in radiation + Co2 = trapped heat.
Source 3: http://www.topnews.in/rising-atmospheric-co2-levels-affecting-stability-west-antarctic-ice-sheet-2141674 This source was written after data was collected by a team of 56 scientists which I believe make it very credible. *The source agrees with Fact 3. It directs the rise of CO2, as a result of global warming and Earth's tilt, to the West Antarctic Ice Sheet (and how its in danger of melting). I agree with this because its a credible source and I realize global warming due to CO2 levels is dangerous.