BLOG | CARIAA Submits its Contribution to the IPCC 1.5°C Special Report

By Evans Kituyi, Program Officer for CARIAA based at the IDRC Regional Office for Sub-Saharan Africa.


Message from Paris

The Paris Agreement resulting from COP21 called for holding the increase in the global average temperature to well below 2°C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5°C. The additional aspirational goal of limiting global warming to 1.5°C above pre-industrial levels caught the world by surprise and has now been agreed as the only safe level of warming for some of the world’s most vulnerable communities. Yet it also revealed a significant knowledge gap on the nature, benefits and feasibility of a 1.5°C warmer world, requiring sound scientific analysis. Responding to this call, the Intergovernmental Panel on Climate Change (IPCC) agreed to prepare a special report in 2018, towards which CARIAA contributed novel insights on the implications for climate hotspots in Africa and Asia.

The Challenge for Research

Leading climate scholars warned against comparing the impacts of 1.5°C and 2°C as this would not yet be scientifically robust, especially for regional scale assessments, if such studies were not appropriately designed. In practice, the assessment of impact is more often based on existing climate experiments, rather than being explicitly designed for the problem at hand. Furthermore, while the literature on 1.5°C impact is sparse, that which has been published to date does not take a strongly regional or hot-spot approach. Yet robust appraisals of climate impact at different levels of global-mean temperature increase are vital to guide assessments of dangerous anthropogenic interference with the climate system. It was hence imperative to conduct dedicated experiments to understand the relative impacts on climate at 1.5°C and 2°C, respectively, to avail meaningful evidence for the Special Report. While the economic constraints of achieving 1.5°C are well known, there was insufficient evidence to distinguish between the benefits of reduced impacts at 1.5°C versus 2°C of warming.

The CARIAA intervention

The demand for regional scale assessments by the Special Report motivated CARIAA to express a desire to contribute. The consortia recognised that the CARIAA hotspot approach to exploring impact and adaptation had the potential to provide novel input regarding semi-arid lands, glacier-fed mountain river basins, and low-lying deltas. Not only does CARIAA take a regional approach, it also aims to synthesise across similar climate hot-spots, allowing inter-regional comparison, and understanding of the implications for the most poor and vulnerable. The literature on 1.5°C is sparse, and that which has been published does not take a regional or hotspot approach. CARIAA could thus provide distinct policy-relevant inputs to the Special Report, addressing both the differential biophysical impacts and socio-economic vulnerabilities between 1.5 and 2.0°C, as well as the adaptation and national to regional policy implications.

CARIAA therefore set out to develop peer-reviewed inputs to the Special Report, on the implications of a 1.5°C global warming for high-vulnerability hot-spots in Africa and Asia.

Key Findings

The DECCMA consortium recognised its potential to improve our current understanding of the impact of sea level rise at 1.5°C and 2.0°C in vulnerable low-lying deltas, whose problems are compounded by sediment starvation and subsidence, leading to salinization, flooding and erosion. Their research focused on the world’s largest delta, the Ganges-Brahmaputra-Meghna (GBM), which is characterised by a high population of mainly poor people. In the GBM, the assessment found that the effects of a +1.5°C world compared with a +2.0°C world may not be discernible until at least the 2040s due to annual variability. However, comparing a +1.5°C world with a +3.0°C world, the average decadal mean depth of flooding may double. The average decadal mean area of land inundated is projected to increase 2.5 times. The researchers also observed that numerous deltas world-wide are under threat from sea-level rise and sediment starvation. Under a high emissions scenario, and without sufficient sedimentation or adaptation, nearly all deltaic land in the regions analysed will be highly exposed to flooding by 2200. Over multiple centuries, climate change mitigation and sedimentation is key to deltas’ survival.


Using data already collected during CARIAA, the HI-AWARE consortium contributed new knowledge on the impact of +1.5°C and +2.0°C on the upstream ice in the Indus Ganges Brahmaputra rivers and the consequent changes in downstream water availability, timing and magnitude of flow. Furthermore, the Ganges-Brahmaputra delta is additionally threatened by increases in flooding events related to the subsidence of land, rising sea levels and increases in tropical cyclone activity over the Bay of Bengal. The consortium learned that these hotspots are experiencing faster than global average warming. A global temperature increase of 1.5°C with respect to pre-industrial levels would imply about 2.1°C temperature increase for the Indus, Ganges and Brahmaputra river basins. Similarly, under a 2.0°C global temperature increase, these river basins would warm up by approximately 2.7°C. The region is facing strong negative impact of climate change for the occurrence of floods, agricultural production, hydropower production, and human health. These changes increase linearly with temperature increase.


The ASSAR consortium recognised their potential to improve knowledge on how different regions and countries in Africa would be impacted under a +2.0 compared to a +1.5 degree scenario. The team analysed projected temperature and rainfall changes in 49 African countries under both scenarios using data from the CMIP5 multi-model archive. Their work found that under RCP 8.5, the African continent as a whole will experience +1.5 and +2.0°C in the year 2025 (2008-2043) and 2043 (2022-2058), respectively. Yet arid and semi-arid countries will warm more rapidly than more humid countries. These countries are more sensitive to heat-related impact. Countries that have continental climate conditions, with large interior regions away from the coast such as Niger, Burkina Faso and northern Mali, also experience greater temperature change. While global precipitation is projected to increase by approximately 3-5% per degree of warming, 30 African countries exhibit a decrease in rainfall at both +1.5 and +2°C (including countries in Southern Africa, western North Africa and western West Africa), while 19 are projected to have increased rainfall. These include much of East Africa and eastern parts of West and North Africa. The differential impact and risks at these two temperature levels were not quantified and is a knowledge gap for future study.


Arid and semi-arid regions exhibit faster rates of relative change in precipitation, regardless of the direction of change. An additional 0.5°C of global warming does matter for African countries, requiring urgency in both efforts to keep as far below 2.0°C as possible to slow the pace of warming, and to invest in resilience to the warming that cannot be avoided.


What the Findings Mean  

In all the three cases, the impact at both +1.5 and +2 degrees is significantly greater than the global average. While there is much autonomous adaptation to today’s climate, there is also a significant amount of planned or engineered adaptations that can have a greater impact on the environment, for example regarding sea level rise. Planned adaptations change the physical landscape in the delta, and it is in this context that people will continue to adapt. Sea-level rise is likely to make sustainable development more challenging, particularly as assets and people living in risky areas are likely to increase. The HI-AWARE team stresses that the even the supposedly safer +1.5°C scenario is not suitable for robust climate change adaptation planning. The formulation of robust climate change adaptation policies must be based on a range of potential future climates. The impact of projected temperature and rainfall changes at +1.5 and +2.0°C will depend strongly on the sensitivity of specific African societies and the livelihoods they depend on.


What CARIAA achieved

In taking on this challenge to contribute to the IPCC Special Report, the CARIAA program made notable achievements. First, the consortia prepared novel analyses and associated scientific activities in a short time that brought together climate science, biophysical and economic impact, vulnerability and policy in light of +1.5°C concerns. This was additional to what the consortia had committed to do. Second, selected CARIAA scientists were supported to participate and present their findings at a pre-scoping meeting and directly engaged authors while they worked on the Special Report. Third, the researchers quickly produced four peer-reviewed articles on the impacts and implications of +1.5°C versus +2°C in each hotspot, in time for the deadlines under the IPCC process. This remarkable undertaking demonstrates CARIAA’s ability to leverage consortia research efforts across the hotspots into evidence that has relevance to a pressing global policy and science issue.



Mitchell et al. (2016) Realising the impacts of a 1.5 degree warmer world. Nature Climate Change, 6 June. Advance Online Publication. Pp1-2.

Schleussner et al. (2016) Differential climate impacts for policy-relevant limits to global warming: the case of 1.5◦C and 2◦C: Earth Syst. Dynam., 7, 327–351.

Mitchell et al (2016) ibid.