1) Wikipedia, Milankovitch Cycles, http://en.wikipedia.org/wiki/Milankovitch_cycles
2) Bard E & Frank M. 2006. Climate change and solar variability: What’s new under the sun? Earth and Planetary Science letters Vol. 248 issue 1-2. pp. 1-14
Figure 1: Global Warming Art Images: http://commons.wikimedia.org/wiki/Category:Global_Warming_Art_images