The IPCC’s 1.5°C Special Report

Claire Fyson and Carl Friedrich-Schleussner attended the IPCC plenary as advisors to the Saint Lucia delegation, providing scientific advice under the framework of the IMPACT project

For four days in late October, the Intergovernmental Panel on Climate Change (IPCC) met in Bangkok for its 44th plenary session. The outline for the forthcoming Special Report on 1.5°C due for adoption in 2018 was to be approved, making this a crucial meeting for vulnerable countries such as the Small Island Developing States and Least Developed Countries.

The IPCC accepted the invitation from the UNFCCC to make this special report at its 43rd session in Nairobi, and a proposed outline had been drawn up during a scientific scoping meeting with 85 experts in August this year.

Their proposal included six chapters, but allocated only one chapter to understanding the impacts of 1.5°C warming, a topic that was central to the request from the UNFCCC (1).

Other proposed chapters covered mitigation pathways and the context of the 1.5°C temperature goal, including approaches for strengthening and implementing the global response to climate change, sustainable development, and poverty eradication.

A number of countries raised concerns that these contextual chapters would not have a sufficient body of peer-reviewed literature to draw from, particularly for research relating to specifically to the 1.5°C issue. Therefore, the plenary decided to merge two of these chapters, resulting in a five-chapter outline.

It was also agreed that a clear message should be given to the future authors of the report that the bullet points in the outline are indicative, and that the material covered should be based on a thorough analysis of the available literature (2). Any research gaps identified during this process will be highlighted so that these can be addressed in later IPCC reports once more literature becomes available.

What will the report cover?

The first chapter will provide the framing and context of the report, including a brief overview of key concepts relating to 1.5°C (e.g. reference levels, probability, overshoot), new material since the AR5 report, and the treatment of uncertainties.

Chapter 2 – mitigation pathways compatible with 1.5°C in the context of sustainable development – will explore the characteristics of pathways for 1.5C, and the constraints, uncertainties, opportunities and challenges associated with these pathways. This chapter will include a comparison of 1.5C pathways with those for higher levels of warming, as well as information on 1.5°C compatible 2025 and 2030 greenhouse gas emission levels as called for by the UNFCCC (3).

Chapter 3 will cover the impacts of 1.5°C on both human and natural systems. The longest chapter of the report, this chapter will cover climate change impacts and vulnerabilities at both global and regional scales, and across different sectors. The assessed impacts will include those that are already observed, those expected at 1.5°C, and those avoided at 1.5°C when compared to higher levels of warming. Crucially for the most vulnerable countries, adaptation and the limits to adaptive capacity will be explored, as well a comparison of slow and fast onset events. As such the report will look at the current status of literature on Loss and Damage.

Chapter 4 looks at how to strengthen and implement the global response to the threat of climate change. This covers the context of the 1.5°C goal, which countries agreed to include in the report during the 43rd session of the IPCC in Nairobi (4). The chapter will explore the assessment of current and emerging adaptation and mitigation options, including capacity limitations, the pace of development and deployment that would be compatible with both 1.5°C and sustainable development, options for implementing far-reaching and rapid change, and case studies of implementation at different scales.

Finally, chapter 5 explores the linkages of 1.5°C with sustainable development, poverty eradication and the reduction of inequality. This includes the positive and negative impacts associated with adaptation and mitigation measures, climate resilient development pathways, and knowledge and experience on these linkages from local to global scales.

Vulnerable countries such as the small island developing states (SIDS) called for more than one chapter on the impacts of 1.5°C to ensure a comprehensive coverage of this key topic and sufficient visibility throughout the report. While they could not push this through the plenary, they managed to secure a range of other improvements.

Overall, the final outline is more focused on the special report’s purpose – to cover the impacts of 1.5°C and the related pathways – than the original proposal. Given that this report will provide essential framing for the long-term temperature goal agreed under the Paris Agreement, it is of utmost importance that it fulfils its purpose.

The outline also sends a strong signal to scientists of the importance of research on 1.5°C. Furthermore, it will require an assessment of the available literature on topics that have been less explored by previous IPCC Assessment Reports, but are increasingly relevant to the work of the UNFCCC, such as limits to adaptation and Loss and Damage.

Other topics for discussion

Aside from the 1.5°C Special Report outline, the meeting also covered a range of other topics from the IPCC’s budget to a methodology report on the refinement of the IPCC’s guidelines on GHG inventories.

The participation of developing countries in the IPCC was also discussed at length, with a number of developing countries highlighting the problems that their scientists face, language barriers being a particular issue for Francophone African countries. In this context, a new initiative by UN Environment for providing access to scientific publications for all IPCC authors through their facilities will be a very welcome resource.

One of the spinoffs from the scoping meeting in August is that a group of scientists have got together to develop a special issue of the journal Regional Environmental Change on 1.5°C and small island developing states, which is now calling for submissions. Editors of this are Adelle Thomas (University of the Bahamas), Mahendra Kumar (Independent Pacific Climate Change Expert) and Carl-Friedrich Schleussner (Climate Analytics).