Summary of the IPCC Summary for Policymakers, Part I

While we would certainly recommend everyone reading the entire IPCC Summary for Policymakers, here are some highlights:

• “The understanding of anthropogenic warming and cooling influences on climate has improved since the Third Assessment Report (TAR) in 2001, leading to very high confidence [a 9 out of 10 chance] that the globally averaged net effect of human activities since 1750 has been one of warming.”
• “The observed widespread warming of the atmosphere and ocean, together with ice mass loss, support the conclusion that it is extremely unlikely [<5% change] that global climate change of the past fifty years can be explained without external forcing.”
• “Most of the observed increase in globally averaged temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.”
• “The global atmospheric concentration of carbon dioxide has increased from a pre-industrial value of about 280 ppm to 379 ppm in 2005. The atmospheric concentration of carbon dioxide in 2005 exceeds by far the natural range over the last 650,000 years (180 to 300 ppm) as determined from ice cores.”
• “The primary source of the increased atmospheric concentration of carbon dioxide since the pre-industrial period results from fossil fuel use, with land use change providing another significant but smaller contribution. Annual fossil carbon dioxide emissions increased from an average of 6.4 GtC per year in the 1990s, to 7.2 GtC per year in 2000–2005.”