Human Influence on Climate Clear, IPCC Report Says

Co-Chair Thomas Stocker concluded: “As a result of our past, present and expected future emissions of CO2, we are committed to climate change, and effects will persist for many centuries even if emissions of CO2 stop.”

Rajendra Pachauri, Chair of the IPCC, said: “This Working Group I Summary for Policymakers provides important insights into the scientific basis of climate change. It provides a firm foundation for considerations of the impacts of climate change on human and natural systems and ways to meet the challenge of climate change.” These are among the aspects assessed in the contributions of Working Group II and Working Group III to be released in March and April 2014. The IPCC Fifth Assessment Report cycle concludes with the publication of its Synthesis Report in October 2014.

“I would like to thank the Co-Chairs of Working Group I and the hundreds of scientists and experts who served as authors and review editors for producing a comprehensive and scientifically robust summary. I also express my thanks to the more than one thousand expert reviewers worldwide for contributing their expertise in preparation of this assessment,” said IPCC Chair Pachauri.

The Summary for Policymakers of the Working Group I contribution to the IPCC Fifth Assessment Report (WGI AR5) is available at www.climatechange2013.org or www.ipcc.ch.

Key Findings

See separate Fact Sheet of Headline Statements from the WGI AR5 Summary for Policymakers, available at www.climatechange2013.org.

Background

Working Group I is co-chaired by Qin Dahe of the China Meteorological Administration, Beijing, China, and Thomas Stocker of the University of Bern, Switzerland. The Technical Support Unit of Working Group I is hosted by the University of Bern and funded by the Government of Switzerland.

At the 28th Session of the IPCC held in April 2008, the members of the IPCC decided to prepare a Fifth Assessment Report (AR5). A Scoping Meeting was convened in July 2009 to develop the scope and outline of the AR5. The resulting outlines for the three Working Group contributions to the AR5 were approved at the 31st Session of the IPCC in October 2009.

The Summary for Policymakers of the IPCC WGI AR5 was approved at the Twelfth Session of IPCC Working Group I meeting in Stockholm, Sweden, 23 to 26 September 2013 and was released on 27 September.

The Final Draft of the Working Group I report (version distributed to governments on 7 June 2013), including the Technical Summary, 14 chapters and an Atlas of Global and Regional Climate Projections, will be released online in unedited form on Monday 30 September. Following copy- editing, layout, final checks for errors, and adjustments for changes in the Summary for Policymakers, the full report of Working Group I will be published online in January 2014 and in book form by Cambridge University Press a few months later.

The Working Group I assessment comprises some 2,500 pages of text and draws on millions of observations and over 2 million gigabytes of numerical data from climate model simulations. Over 9,200 scientific publications are cited, more than three quarters of which have been published since the last IPCC assessment in 2007.

In this IPCC assessment report, specific terms are used to indicate the assessed likelihood of an outcome or a result. For those terms used above: virtually certain means 99–100% probability, extremely likely: 95–100%, very likely: 90–100%, likely: 66–100%. For more information see the

IPCC uncertainty guidance note: https://www.ipcc-wg1.unibe.ch/guidancepaper/ar5_uncertainty- guidance-note.pdf