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View of the dais during the plenary session at the 54th Session of the IPCC Bureau and 46th Sessions of the IPCC, Montreal. Photo by IISD/ENB | Mike Muzurakis
15 September 2017 13:33

Guest post: What will be in the next IPCC climate change assessment

Dr Valérie Masson-Delmotte

Dr Valérie Masson-Delmotte

15.09.2017 | 1:33pm
Guest postsGuest post: What will be in the next IPCC climate change assessment

Dr Valérie Masson-Delmotte is a senior researcher at the Laboratoire des Science du Climat et de l’environnement in France and co-chair of Working Group 1 of the Intergovernmental Panel on Climate Change (IPCC).

At a meeting in Montreal last week, the member countries of the United Nations reached an important decision about the next few years of the IPCC – the scientific body that assesses climate change. All countries agreed on the outlines for the three main components of the next major report, due in 2021-22, which is the vital groundwork that will now guide the contributions of climate change researchers from all over the world.

My colleagues and I at Working Group 1 (WG1) – the group that examines the physical science basis underpinning past, present and future climate change – have taken a brand new approach that we think will make our work more accessible, holistic and in tune with policymakers’ needs.

Assessing evidence

Every five or six years, the IPCC performs an exhaustive assessment of the state of knowledge on all aspects of climate change, through a thorough analysis of the scientific literature.

These reports are the work of hundreds of volunteer scientists – selected to be lead authors, coordinating lead authors and review editors – as well as thousands of experts who review the drafts. The sixth report in the series is due in 2021 and 2022, and will be known as the Sixth Assessment Report (AR6).

Dr Valérie Masson-Delmotte at IPCC-46 and Working Group I, II, III Sessions in Montreal, Canada, 6 – 10 September 2017

My colleague Prof Panmao Zhai and I are the co-chairs of WG1, which deals with the scientific aspects of the climate system. This includes, for example, temperature, precipitation (rain and snow), sea level trends and extreme events. The second working group (WG2) looks the vulnerability of socio-economic and natural systems to climate change, consequences and options for adaptation. The third working group (WG3) explores pathways for limiting greenhouse gas emissions, known as climate change mitigation.

Before we embark on the big assessment reports, it is important to scope out what they need to cover – a bit like a table of contents. Since IPCC reports are prepared for all governments, every country needs to agree on this outline. That is what we were all doing in Montreal last week.

Late on Sunday afternoon, the final outline for the WG1 report was unanimously agreed. So what will it look like?


The outline consists of 12 chapters. The first is the framing, then three chapters are dedicated to large-scale patterns of climate change. These are: the changing state of the climate system, the assessment of human influence, and future climate change. This last chapter will encompass both near term prediction and scenario-based long term projections.

The second set of chapters is dedicated to key processes that shape the response of the climate system. These are: carbon and other biogeochemical cycles and their feedbacks; short-lived climate drivers; Earth’s energy budget, climate feedbacks and climate sensitivity; and water cycle changes, the ocean, cryosphere and sea level change.

Each of these chapters will have an “end-to-end” approach, which means that they will combine observations, palaeoclimate, process studies, theory and modelling into a complete picture. They are essentially a “one-stop-shop” for each topic.

The last set of chapters will be dedicated to regional climate information, and will fit closely will the assessment of regional climate change impacts in the WG2 report. There will be a chapter on the assessment of methodologies linking global to regional climate change, one full chapter on weather and climate extreme events, and our final chapter on climate change information relevant for assessing regional impacts and for risk assessment.

The proposed new outline marks a significant evolution from the two previous WG1 assessment reports (known as “AR4” and “AR5”), which have taken a roughly similar format to each other.

Our new outline builds on considerable progress in scientific understanding and research practices, as well as on the outcomes of three IPCC workshops on regional climate projections, communication, and risks and solutions.


This new outline is a result of our “scoping” process. First, we sought the input of a IPCC member countries, observer organisations and the international research community through a series of pre-scoping consultations. For the second step, we selected an international group of 180 scientists to join a scoping meeting in Addis Ababa, Ethiopia in May 2017, to undergo some collective brainstorming.

The result was a proposed list of chapters, complete with titles and indicative bullet points and a logical narrative that will make it easier for users to find the information they need.


One thing we thought carefully about in the scoping process was the need for the chapters to “talk” to each other and exchange information, to ensure the coherence of the assessment. For this, we will have a series of “technical annexes” that will deal with methodological topics common to two or more chapters, such as observational datasets or model evaluation.

A second dimension of the report design is its policy relevance. We considered the intersections between the physical science basis and multiple other dimensions, and came up with a number of “handshakes” between the authors of our report and the other working groups. For instance, the WG1 chapter on short-lived climate forcers is connected to the potential for, and co-benefits of, their mitigation (WG3). It is also related to implications for air quality, which is one element of assessing the impacts of climate change on health in WG2.

A final important aspect of our new outline is that it is designed to complement and build on the three special reports that are already underway.

The idea of special reports is that they are smaller than the main assessment reports and focus on a specific topic of interest. The first one is on global warming of 1.5C (the first draft of which is currently out for expert review). The second special report is on the oceans and cryosphere in a changing climate and the third is on climate change and land. AR6 will revisit the findings of these special reports and update them on the basis of new lines of evidence. New results from climate model simulations performed under the sixth phase of the Climate Model Intercomparison Project (CMIP6) will be available by the time of AR6, for example.

We are confident that this new outline will motivate high-profile researchers from all around the world to participate in AR6, to help us deliver an assessment of the state of climate science knowledge that is unparalleled in both scope and quality.

There are a number of ways to get involved. Publishing new scientific papers means they could feed into the new report. Scientists can also be nominated by their country’s focal point to be authors or appointed as a contributing author by the author teams – these nominations will be coming soon.

And finally, another way to participate is to be invited, or volunteer, as an expert reviewer. IPCC reports all undergo a multi-stage review process, and drafts are widely circulated to independent experts all over the world with significant expertise in particular areas of the report.

Thousands of scientists from all over the world participate in the IPCC review process as expert reviewers (you can read more about the process here). Keep an eye out for when the applications open for reviewers for AR6.

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