Greenhouse gases are the cause of Greenhouse effect.The greenhouse gases which include CO2, Methane etc. trap the heat in the Earth's atmosphere and don't allow it to escape.
The weapon is fitted with a Leupold Mark 4. The rifle is also similar in appearance to the TAC-338 rifle that Kyle used in real life. McMillan TAC-338A sniper rifle with Harris bipod, Leupold Mark 4 scope, and AN/PVS-22 Universal Night Sight - .338 Lapua Magnum. Kyle taking aim with the rifle. Right side of the rifle.
Ex-Marine Eddie Ray Routh shot and killed Chris Kyle and Chad Littlefield at a shooting range where they were trying to help him tackle his PTSD. Routh will go on trial in February shortly after full release of American Sniper, the movie tipped for Oscars which tells story of Kyle's life.