In its latest landmark assessment of the future of the planet under global warming, the Intergovernmental Panel on Climate Change of the United Nations concluded that it is "extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century."
The panel, which released its first batch of findings on Friday, said the evidence for its conclusion has grown stronger due to "better observations, an improved understanding of the climate system response and improved climate models."
"Warming in the climate system is unequivocal and since 1950 many changes have been observed throughout the climate system that are unprecedented over decades to millennia. Each of the last three decades has been successively warmer at the Earth's surface than any preceding decade since 1850," according to the panel's 20-page Summary for Policymakers of the IPCC Working Group I assessment report. The document was approved early this morning in Stockholm, Sweden by government officials from more than 120 countries who spent days wrangling with scientists over the final text.
For the first time, the IPCC specifies that the world needs to stick to a "carbon budget" and specifies the levels of future carbon emissions that are allowable in order to have a reasonable chance of staying within 2 degrees Celsius of warming in this century, the safe climate target. In short, to have a two-in-three probability of not crossing the danger mark, the world is allowed to burn, at most, 1,000 gigatons of carbon in total since the Industrial Revolution, and countries have already used up more than half that budget.
"Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system," said Thomas Stocker, co-chair of Working Group I. "Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions."
The Working Group I assessment, the IPCC's fifth since 1990, is about 2,500 pages long and draws on millions of observations and over 2 million gigabytes of numerical data from climate models, according to the IPCC. The review cites some 9,200 scientific publications, most of which were published since the last IPCC assessment in 2007.
Working Group I Contribution to the IPCC Fifth Assessment Report
Climate Change 2013: The Physical Science Basis
Summary for Policymakers