IPCC (4. mai 2007). «Summary for Policymakers»(PDF). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Henta 3. juli 2009.
Hegerl, Gabriele C.; et al. (2007). «Understanding and Attributing Climate Change»(PDF). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC. Arkivert frå originalen(PDF) 8. mai 2018. Henta 26. juni 2010. «Recent estimates indicate a relatively small combined effect of natural forcings on the global mean temperature evolution of the second half of the 20th century, with a small net cooling from the combined effects of solar and volcanic forcings.» CS1 maint: Explicit use of et al. (link)
Hegerl, Gabriele C.; et al. (2007). «Understanding and Attributing Climate Change»(PDF). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. IPCC. Arkivert frå originalen(PDF) 8. mai 2018. Henta 26. juni 2010. «Recent estimates indicate a relatively small combined effect of natural forcings on the global mean temperature evolution of the second half of the 20th century, with a small net cooling from the combined effects of solar and volcanic forcings.» CS1 maint: Explicit use of et al. (link)