The IPCC Fourth Assessment Report

The Fourth Assessment report was released in three installments over the course of 2007, with the final synthesis report published in November 2007. More than 450 lead authors received input from more than 800 contributing authors, and an additional 2,500 experts reviewed the draft documents.

Working Group I - "The Physical Science Basis"

February 2, 2007

C2ES summary of Working Group I: "The Physical Science Basis"

This report assesses the current state of knowledge about the natural and human drivers of climate change, reflecting the progress of the climate change science in the observation of the atmosphere, the Earth's surface and oceans. It provides a paleoclimatic perspective and evaluates future projections of climate change. Main topics include changes in atmospheric composition, observation of various climate parameters, coupling between changes in climate and biogeochemistry, evaluation of models and attribution of climate change.

It answers such questions as:

  • What progress has been made in understanding and attributing climate change?
  • What do observations of the atmosphere, oceans, sea level, snow and ice tell us?
  • How has climate been behaving in the last hundreds of thousands of years?
  • What are the projections of future changes?

Working Group II - "Impacts, Adaptation & Vulnerability"

April 6, 2007

C2ES summary of Working Group II: "Impacts, Adaptation & Vulnerability"

This installment provides a detailed analysis of observed changes in natural and human systems and the relationship between those observed changes and climate change, as well as a detailed assessment of projected future vulnerability, impacts, and response measures to adapt to climatic changes for main sectors and regions.

It answers such questions as:

  • What is the current state of knowledge on impacts of climate change?
  • What is the state of knowledge on impacts under different levels of adaptation?
  • What are the impacts under different levels of mitigation?
  • What is the state of knowledge concerning observed effects?

Working Group III - "Mitigation of Climate Change"

May 4, 2007

C2ES summary of Working Group III report on mitigation

The WGIII report analyzes mitigation options for the main economic sectors in the near-term. It also provides information on long-term mitigation strategies, paying special attention to implications of different short-term strategies for achieving long-term goals. This installment also addresses the relationship between mitigation and sustainable development.

It answers such questions as:

  • What have been the greenhouse gas emission trends in the last three decades?
  • What can we expect for energy and emission trends in the next 30 years?
  • What are the options for greenhouse gas mitigation across different economic sectors in the short and medium term (until 2030) and in the long-term (beyond 2030)?
  • How do the time scales of climate system responses relate to the time scales for mitigation and adaptation?
  • What are the opportunities for integrating sustainable development and climate change mitigation activities?

Synthesis Report

Nov. 17, 2007

C2ES summary of synthesis of report

The Summary for Policymakers of the IPCC Fourth Assessment Synthesis Report represents the IPCC’s most comprehensive and definitive statement to date on climate change. Among the highlights of its findings:

  • There is strong certainty that most of the observed warming of the past half-century is due to human influences, and a clear relationship between the growth in manmade greenhouse gas emissions and the observed impacts of climate change.
  • The climate system is more vulnerable to abrupt or irreversible changes than previously thought.
  • Avoiding the most serious impacts of climate change ­-- including irreversible changes – will require significant reductions in greenhouse gas emissions. 
  • Mitigation efforts must also be combined with adaptation measures to minimize the risks of climate change.