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Skeptical Science has just posted A Comprehensive Review of the Causes of Global Warming. The review’s conclusion are well illustrated by this figure which attributes the inputs from human and natural causes over the last 50 years.

Net human and natural percent contributions to the observed global surface warming over the past 50-65 years according to 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), and Gillett et al. 2012 (G12, orange).

The different colours show the different studies reviewed. These used different and independent methods and Skeptical Science concludes they “provide multiple lines of evidence that humans are the dominant cause of global warming over the past century, and especially over the past 50 to 65 years.”

These studies considered different human and natural causes:

  • Human greenhouse gas (GHG) emissions,
  • Solar activity,
  • Volcanic activity,
  • Human aerosol emissions,
  • The El Niño Southern Oscillation (ENSO).

GHG and human aerosol (primarily sulphur dioxide, SO2)  are the two largest human influences, and solar and volcanic activity and ENSO are the dominant natural influences on global temperature. The figure below illustrates the breakdown of their contributions in these studies.

Percent contributions of various effects to the observed global surface warming over the past 100-150 years according to 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), Stott et al. 2010 (S10, gray), and Huber and Knutti 2011 (HR11, light blue).

Clearly, human inputs have provided the largest effect on global temperature over recent years. Greenhouse gas emission have had a positive effect and aerosol emissions a negative, partly balancing, effect. This negative human factor is decreasing as humanity cleans up its act in terms of SO2 and other aerosol pollution.

As Skeptical Science summarises these findings:

“A wide variety of statistical and physical approaches all arrived at the same conclusion: that humans are the dominant cause of the global warming over the past century, and particularly over the past 50 years.  This robust scientific evidence is why there is a consensus amongst scientific experts that humans are the dominant cause of global warming.”

Our fingerprints are all over it!

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