http://www.nationalgeographic.com/environment/global-warming/global-warming-causes/
http://timeforchange.org/main-cause-of-global-warming-solutions
http://www.greenpeace.org/international/en/campaigns/climate-change/coal/Coal-mining-impacts/
https://www.scientificamerican.com/article/copious-fertilizer-down-on-the-farm-means-more-global-warming-pollution-up-in-the-sky/
https://www.scientificamerican.com/article/deforestation-and-global-warming/
http://www.conserve-energy-future.com/GlobalWarmingCauses.php