The IPCC reports are included in “assessment cycles” which are referred to with a number and each assessment period lasts five years. It is also important to note that all types of IPCC reports listed below are available for free to the general public directly on the IPCC Web site. [3]
3.1. The Assessment Reports
Within one assessment cycle, the IPCC Assessment Reports are produced following different steps including first and second order drafts, reviewed by hundreds of independent international expert scientists, on a voluntary basis. Expert reviewers are selected after a IPCC application process based on their international background, experience, and previous publications. The chosen expert reviewers are hired based on the diversity of their background to ensure that as many ideas as possible are considered for a rich perspective on different topics. Each reviewer's comment is taken into account, ensuring that the reports are transparent and reliable.
For every IPCC report, an order of magnitude of thousands of articles from both peer-reviewed articles and grey literature are evaluated. This quasi-comprehensive review allows the widest possible range of scientific output to be considered.
In the more recent assessment cycle, for example, the decision to deliver the Sixth Assessment Report - also referred to as AR6 - was taken during a meeting in February 2015 named the IPCC 41st Session, in the city of Genova.
3.2. Special Reports
The IPCC can also issue Special Reports, for instance at the request of a government for more scientific information on a particular matter. In 2019, the IPCC delivered three Special Reports:
- A Special Report on Global Warming of 1.5°C.
- A Special Report on the Ocean and Cryosphere in a Changing Climate.
- A Special Report on Climate Change and Land.
The Special Reports provide an interdisciplinary evaluation of those topics and involve more than one Working Group. The Special Reports are less dense in terms of volume and content than the regular IPCC Assessment Reports.
3.3. The Synthesis Reports
The Synthesis Reports concentrate on a number of important policy issues. They include the inputs coming from the Assessment Reports and the inputs from the Special Reports produced during a given 5-year assessment period. The Synthesis Reports contain several chapters and may also include a Technical Summary.
The Synthesis Report within the Sixth Assessment Report is due to be delivered in the second trimester of 2022. It will include all contributions from the three working groups expected to be implemented in 2021.
3.4. The Summary for Policymakers (SPM)
Within each assessment period, around fifty scientists are chosen and join the efforts of the Working Groups to deliver a first order draft of another type of IPCC report called the Summary for Policymakers (SPM), mainly intended for government leaders. Such a report involves a separate development process and is based on consensus for the framework.
First, each Working Group synthesizes its inputs coming from the Assessment Report in a first draft of the SPM. This proposed report must then be endorsed line-by-line by government officials through a dedicated discussion process to agree on a final version of the text. Sentences are displayed on a screen visible to all participants, and as part of the rewriting process, paragraphs are added or deleted as required.
The new draft is reviewed during a plenary session including both national government delegates and observers. The plenary sessions are placed under the complete supervision of the different Working Group Chairs to make sure that the scientific message is faithfully translated into a framing designated to the policymaking area.
This review process aims at clarifying the message of the SPMs while preserving the core of the scientific inputs. As for the policymakers’ representation, each delegation sends about six representatives including their local experts that may belong to the IPCC, as well as other public officials or experts of diplomacy/negotiations.
In case of major disagreement, a small group with the main actors involved is created by a Working Group Chair to expedite the process and negotiate a mutually agreeable framework.
3.5. The Methodology Reports
Another kind of documents produced by the IPCC are the Methodology Reports. Their purpose is to deliver operational advice regarding the elaboration of national greenhouse gas inventories. They contain an “Overview Chapter” with the inputs of the Summary for Policymakers.
All the Reports described above may also contain a section named “Frequently Asked, Questions” as well as a section called “Supplementary Material”.
3.6. An example of the IPCC report’s impact
The direct impacts of the IPCC's extensive work are not necessarily easy to measure. However, in some cases, their consequences in terms of political decision are clearly identifiable. The most impactful reports regarding public and political awareness on climate change are certainly the summaries for policymakers with synthesized information on critical conclusions from the main Assessment or Special Reports.
As an example, the European Green New Deal announced by Ursula von der Leyen during COP25 in 2020 directly quotes the scientific findings of the IPCC 1.5°C report to substantiate the targets set, including a proposal to implement climate legislation to achieve climate neutrality by 2050. [4] More globally, the international texts of the United Nations Framework Convention on Climate Change (UNFCCC) are based on the results presented in the IPCC reports.
