Insights and Commentaries

Insights and Commentaries

Institute’s experts review the upcoming IPCC Sixth Assessment report

8th April 2021

Every five to seven years, the Intergovernmental Panel on Climate Change (IPCC) publishes comprehensive scientific assessment reports. The latest of these reports was the Fifth Assessment Report (2014) that provided the main scientific input to the Paris Agreement 

Since the Fifth Assessment Report was published, the IPCC has released several major deliverables, including the Special Reports on Global Warming of 1.5°Climate Change and Land, and Ocean and Cryosphere. 

The upcoming Sixth Assessment Report is currently being prepared and the experts of the Global CCS Institute have participated as expert reviewers of the draft report on climate change mitigation, prepared by the Working Group III of the IPCC.  

What is the Sixth Assessment Report? 

The Sixth Assessment Report will provide a comprehensive summary of what is known about the drivers of climate change, its impacts and future risks, and how mitigation and adaptation can reduce those risks. The scientists authoring the report volunteer their time to assess thousands of scientific papers published each year to provide a comprehensive overview of the latest available information.  

The IPCC has three working groups: Working Group I, dealing with the physical science basis of climate change; Working Group II, dealing with impacts, adaptation and vulnerability; and Working Group III, dealing with the mitigation of climate change. The Sixth Assessment Report will consist othe three Working Group contributions and a Synthesis Report, which integrates the Working Group assessments and the three Special Reports (listed above) produced during the cycle. 

The upcoming report includes new elements. Among these are a chapter on demand, services and social aspects of climate change mitigation, and a chapter dedicated to innovation, technology development and transfer.  

The expert review  

The review process is critical for ensuring the assessment is scientifically rigorous, exhaustive, objective and transparent. 

Given that CCS is a set of climate change mitigation technologies, the experts of the Global CCS Institute have participated as expert reviewers of the draft report on climate change mitigation, prepared by the Working Group III of IPCC. The comments to the First Order Draft were submitted in March 2020, and to the Second Order Draft and the First Draft of the Summary for Policymakers in March 2021. 

"Comments from experts and governments on these and other parts of the report are an essential step in delivering a high-quality final draft."


Jim Skea and Priyadarshi Shukla

Working Group III Co-Chairs

Source: IPCC

After the expert review of the First Order Draft, author teams prepare a Second Order Draft of the report, taking into account the review comments received; a first draft of the report’s Summary for Policymakers is also prepared. These are subject to simultaneous review by experts and governments.  

The upcoming Synthesis Report draft undergoes a single simultaneous government and expert review; followed by a government review of the final draft through the Final Government Distribution.

Figure 1. Expert review in the IPCC report preparation process.  
Source: adjusted from IPCC  


The review process delivers a substantive amount of comments. For example, the Fifth Assessment Report received a total of 142,610 comments. The transparent process foresees that the authors respond to every submitted comment. Eventually, all drafts along with the reviewer comments and the respective responses by the authors are made public when the final reports are published. 

CCS in the Sixth Assessment Report 

The Working Group III contribution (on climate change mitigation) to the assessment report is most relevant for CCS and this is where the experts of the Global CCS Institute have submitted two rounds of comments. 

Expert reviewers cannot cite, quote or distribute the drafts they review because the report is a work in progress. This being said, one of the main expectations for the CCS community going into the Sixth Assessment cycle was the fact that by the time the next assessment report is finalized, a lot more literature on the different applications of CCS technologies will be available. 

The authors of the Sixth Assessment Report have access to an increasing body of literature on all aspects of CCS compared to what was available when the Fifth Assessment Report and the Special Report on Global Warming of 1.5°C were prepared.  

In addition to peer-reviewed scientific, technical and socio-economic literature, the IPCC recognizes that other sources, including reports from governments, industry, and research institutions, international and other organizations, may also provide crucial information for IPCC Reports. This is how the annual Global Status of CCS reports and other specific reports by the Global CCS Institute feed into the process of preparing the Sixth Assessment Report. 

Next steps 

The contributions of the three IPCC Working Groups to the Sixth Assessment Report are all expected to be finalized in 2021The concluding Synthesis Report, due to be finalized in the first half of 2022, will integrate the three most recent IPCC Special Reports on Global Warming of 1.5°C, Climate Change and Land, and The Ocean and Cryosphere in a Changing Climate, as well as the contents of the three Working Group contributions. 

The Global CCS Institute is an accredited observer of the IPCC and will continue to follow the IPCC work in this capacity. 

Read more 

IPCC Factsheet: How does the IPCC review process work? IPCC, 2018 

What is an Expert Reviewer of IPCC reports? IPCC, 2020 

This piece was written by Eve Tamme, our Brussels-based Senior Advisor for Climate Change Policy.

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