Scientists are more certain than they have ever been that humans are causing global warming, according to the most comprehensive report ever conducted into climate change, which predicts "with 95% certainty" that people's greenhouse gas emissions are heating the world.
The degree of certainty leaves little doubt that greenhouse gases such as carbon dioxide and methane are responsible for climate change and compares to a finding of 90% certainty in the previous – fourth – assessment six years ago. This, in turn, was a significant increase on the 66% certainty reached in 2001's third assessment and just over 50% in 1995.
AR5 has 840 main authors recruited from 38 of the IPCC's 195 member countries, with British and American scientists making the biggest contribution.
At more than 3,000 pages, the report is so big that it will be released in three parts over the next 14 months. The first part, released yesterday, covers the physical science of climate change. The second installment will concentrate on the impacts of climate change and how to adapt to them, while the third will examine ways to curb the warming.
As with the other IPCC reports, AR5 is a synthesis of the findings of thousands of peer-reviewed research papers from the past few years. It comes at a crucial time in global climate change politics, since it will be the last IPPC report published before the Paris summit in 2015, when the world's governments have pledged to reach hugely ambitious and legally binding targets to reduce their emissions.
Yesterday US Secretary of State John Kerry backed the report's findings and pledged action on cutting emissions.
He said: "Boil down the IPCC report and here's what you find: Climate change is real, it's happening now, human beings are the cause of this transformation and only action by human beings can help to save the world from its worst impacts.
"This isn't a run-of-the-mill report to be dumped in a filing cabinet. This isn't a political document produced by politicians. It's science."
UN Secretary General Ban Ki-Moon added: "This new report will be essential for governments as they work to finalise an ambitious legal agreement on climate change in 2015.
"To add momentum, I will convene a climate summit in September 2014 at the highest level. The heat is on. Now we must act."