"Some findings go far beyond what we were able to provide in AR4," said Rajendra Pachauri, chair of the IPCC at a press conference on Friday morning, a few hours after the 5 am approval of Working Group I's summary for policymakers following four days of negotiations.

As in AR4, Working Group I found that warming of the climate system is unequivocal, but this time round the assessment report adds that "since the 1950s, many of the observed changes are unprecedented over decades to millennia" and that "each of the last three decades has been successively warmer at the Earth's surface than any preceding decade since 1850".

According to Thomas Stocker, co-chair of Working Group I, scientists can reconfirm that warming is unequivocal and this is now based on multiple lines of evidence from all components of the climate system.

This time the working group has released 18 headline messages from the summary for policymakers, condensed into less than 2 pages of print. "One hundred and ten governments have found consensus over 18 short headlines," said Stocker at the press conference.

For the first time, the full report includes an Atlas of Global and Regional Climate Projections containing climate data that will be freely available to all. "We hope that this will be useful to a wide range of the public," said Stocker. The draft version of the full report will be available on Monday 30th September.

Climate models have improved since the fourth assessment report, the scientists say. "Models reproduce observed continental-scale surface temperature patterns and trends over many decades, including the more rapid warming since the mid-20th century and the cooling immediately following large volcanic eruptions," says one of the headline statements.

The fifth assessment report used four new scenarios for greenhouse gas emissions, known as representative concentration pathways, RCP2.6 (which would produce an approximate total radiative forcing of 2.6 W per square metre in 2100 relative to 1750), RCP4.5, RCP6.0, RCP8.5.

"The future of the world is quite different depending on our choices," said Stocker, speaking about temperature evolution. "Warming will continue under every scenario. The global surface temperature change by the end of the 21st Century is likely to exceed 1.5°C relative to 1850 for all scenarios."

The headline statement on this says that "global surface temperature change for the end of the 21st century is likely to exceed 1.5°C relative to 1850 to 1900 for all RCP scenarios except RCP2.6. It is likely to exceed 2°C for RCP6.0 and RCP8.5, and more likely than not to exceed 2°C for RCP4.5."

Michel Jarraud, secretary-general of the World Meteorological Organization, said that some have seen the lower estimates of temperature rise and argued that we have time, but the lower band "only comes" if there is "quick and aggressive action". He added: "if we don't take action quickly now we are not looking at the first scenario [RCP2.6]". What's more, the temperature increase will not be uniform. "One of the biggest impacts will be on the water cycle."

Stocker showed a plot from the Working Group I report that indicates a linear relationship between temperature anomaly relative to 1861-1880 and cumulative emissions of anthropogenic carbon dioxide since 1850. "The higher the cumulative emissions are the warmer it gets," he said. "It doesn't so much depend on the scenario."

According to Pachauri, one effective instrument for preventing increased emissions would be to put a price on carbon. Regulation and informing the public are options but it's probably only through the market that there'll be a large and rapid enough response. "The IPCC cannot advocate it," he added, "it's for decision-makers to see what's required."

Reporting process

There were 3000 nominations of scientists to work on the fifth assessment report, over 50% more than last time, Pachauri revealed. From these were selected 831 authors and review editors, 60% of them new to the process.

Working group I has looked at 9200 scientific publications, roughly two-thirds of them published since 2007, the year of the fourth assessment report. The summary for policymakers contains roughly 13,000 words while the full report Climate Change 2013: The Physical Science Basis, due to be released in draft form on Monday, contains more than one million words.

Stocker said that 110 governments have looked at the summary for policymakers over the last 4 days, that the team received comments for almost all words, and sometimes paragraphs were discussed for more than an hour. As of this morning, the team had worked "almost incessantly" for the past 52 hours, sleeping for only 6 of them.

Many of the changes made during the discussions were for clarity, according to the co-chair. "The scientists were challenged by governments to tell in simple words what our assessment is," said Stocker. "We kept the 18 key messages, convincing the policymakers this is a consensus. I am very proud as what we've come out with is clearer and more usable language but the essence is not changed in any way."

The last word goes to Achim Steiner, executive director of the UN Environment Programme, who said, via video link from Nairobi, that the IPCC reports are "the yardstick of an elusive quest for perfect knowledge".

• The final draft of the Working Group I report, including the technical summary, 14 chapters and an Atlas of Global and Regional Climate Projections, will go live online on Monday 30th September. The full report will be published online in January 2014 and in book form later in the year. Working group II and Working Group III will release their results in March and April 2014.

This article was amended at 17.35 on 27.9.13 to include the paragraph starting "The headline statement on this....".

This article was updated on 30.9.13 to include links to the final draft of the full report.