1. http://www.unep.org/geo/geo5.asp
2. http://www.unep.org/geo/pdfs/geo5/Measuring _progress.pdf
3. http://siteresources.worldbank.org/EXTANNREP2013/Resources/9304887-1377201212378/93058961377544753431/1_AnnualReport 2013_EN.pdf
4. State of the World: Is Sustainability Still Possible?,2013
5. http://www.ipcc.ch/pdf/assessmentreport/ar5/wg2/ ar5_wgII_spm_en.pdf