Human vs. Natural Contributions to Global Warming

The percentage contribution to global warming over the past 50-65 years is shown in two categories, human causes (left) and natural causes (right), from various peer-reviewed studies (colors).  The studies used a wide range of independent methods, and provide multiple lines of evidence that humans are by far the dominant cause of recent global warming.  Most studies showed that recent natural contributions have been in the cooling direction, thereby masking part of the human contribution and in some cases causing it to exceed 100% of the total warming.  The two largest human influences are greenhouse gas (GHG) and sulfur dioxide (SO2) emissions, mostly from burning coal, oil, and natural gas (sulfur emissions tend to have a net cooling effect).  The largest natural influences on the global temperature are the 11-year solar cycle, volcanic activity, and the El Nino Southern Oscillation (ENSO).

The studies are Tett et al. 2000 (T00, dark blue), Meehl et al. 2004 (M04, red), Stone et al. 2007 (S07, green), Lean and Rind 2008 (LR08, purple), Huber and Knutti 2011 (HK11, light blue), Gillett et al. 2012 (G12, orange), Wigley and Santer 2012 (WG12, dark green), Jones et al. 2013 (J13, pink), IPCC AR5 (IPCC, light green), and Ribes et al. 2016 (R16, light purple).  The numbers in this summary are best estimates from each study; uncertainty ranges can be found in the original research.


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