1. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_spm.pdf
2. http://www.esrl.noaa.gov/gmd/ccgg/trends
3. Rosenzweig, C. et al. Nature 453, 353–358 (2008).
4. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr_spm.pdf
5. http://www.columbia.edu/%7Ejeh1/mailings/20081229_DearMichelleAndBarack.pdf