The IPCC's Special Report on 1.5°C

The 1.5°C Special Report

The latest IPCC special report, released on October 8, follows COP21 and the signing of the Paris Agreement, in which countries commit to taking action to “to limit 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 above pre-industrial levels.” The IPCC was asked to produce a report addressing on the impacts of global warming of 1.5 °C compared to preindustrial levels, and on greenhouse gas emission trajectories. While this report has been widely discussed in the press, it is important to understand its implications and limitations and to identify its main conclusions—both explicit and implied.

Key Messages

EVERY HALF DEGREE COUNTS

One of the key messages of this special report is the idea that “every half degree counts.” The consequences, which are already disastrous at 1.5°C, are far more severe at 2°C. Furthermore, recent studies suggest that once this threshold is crossed, rising temperatures could trigger a series of domino effects—most of them irreversible—linked to the melting of ice and permafrost, changes in ocean circulation, and so on… These effects would lead to changes far more drastic than those currently predicted, transforming the environment beyond anything humanity has ever observed. Limiting global warming to the lowest possible level may be even more critical than the report suggests.

THE SOLUTIONS MENTIONED ARE TECHNICALLY FEASIBLE, BUT…

The report describes the Technical and theoretical feasibility of pathways to limit global warming to 1.5°Cand proposes actions to be implemented in order to meet this objective. In this context, Reducing emissions well before 2030 is an essential requirement. The authors emphasize, on the one hand, the absolute urgency of taking action and, on the other hand, the difficulties involved in deploying technologies that have never been used on such a large scale. Furthermore, the uncontrolled development of these technologies may conflict with the preservation of biodiversity or human development. We cannot simply assume that development and innovation will be enough to offset emissions resulting from human activities. To meet the goal of limiting global warming to 1.5°C, a drastic and immediate reduction in emissions and a technological breakthrough on an unprecedented scale are necessary. However, the likelihood of observing these two phenomena in the coming years has been decreasing day by day since the IPCC’s first report in 1988. As a reminder, We are currently on track for a 3°C rise in temperature by the end of the century, if and only if the commitments under the Paris Agreement are met…

A Detailed Look at the Report's Key Points

1.5°C of global warming

• The historical impact of human activities on global warming is estimated to be approximately 1°C compared to pre-industrial levels. It is likely that this warming will reach 1.5°C between 2030 and 2052, if greenhouse gas emissions continue at the current rate.
• This warming trend is irreversible on a human timescale, and the climate changes caused by rising GHG concentrations in the atmosphere will continue over the coming decades and centuries.
• Limiting global warming to 1.5°C would significantly reduce the risks to natural and human systems compared with a temperature increase of 2°C(the most widely held optimistic estimate at present).
• The commitments made under the Paris Agreement are clearly not enough to limit global warming to 1.5°C. Current national commitments are putting us on a path toward a 3°C temperature increase by the end of the century, with warming continuing beyond that point.

Climate Projections and Associated Impacts

• The risks associated with a 1.5°C rise in temperature (health, food security, etc.) would be significantly reduced compared to a 2°C rise, including, among other things: - a 10-cm reduction in sea-level rise compared to the 2°C scenario, meaning 10 million fewer people affected; - the preservation of 1.5 to 2.5 million km² of permafrost¹, with significant implications for methane storage; - a population exposed to water shortages that is half as large as under the 2°C scenario;
• The difference is also significant in terms of biodiversity and ocean acidification (preservation of 30% of coral reefs).

 Impacts and risks to natural and human systems based on the level of warming (purple: very high probability of severe and irreversible impacts / red: severe and widespread impacts / yellow: impacts detected and attributable to climate change / white: no detectable attributable impacts)

The Various Possible Paths

• The report explores several theoretical scenarios for staying within the 1.5°C target. CO2 emissions must be reduced by 45% by 2030, reaching net-zero around 2050 (20 to 25 years earlier than in the 2°C scenario).Emissions of other greenhouse gases follow a similar trajectory in both scenarios.
• The report outlines four main roadmaps that differ depending on changes in global demand and the major energy policies chosen (particularly with regard to electricity sources).
• In any case, The necessary changes are drastic, occurring at a pace of transformation never before seen on a large scale. A drastic reduction in emissions is needed across all sectors. A wide range of technical solutions must be scaled up quickly.
• CO2 capture technologies are included in all of these roadmaps. However, the development of these methods faces numerous technical, social, and environmental constraints (land use, reforestation, etc.). In particular, this raises potential issues regarding biodiversity and food security if these techniques are not deployed in a controlled and sustainable manner. Rapidly reducing emissions is therefore all the more vital, given that large-scale deployment of these technologies will take time.
• Avoiding exceeding the 1.5°C threshold (and thus potentially irreversible consequences) and dependence on CO₂ capture technologies—which have not been tested on a large scale—requires a reduction in emissions well before 2030.
• Efforts to combat global warming should minimize potential negative impacts on the development of the poorest populations (who are often the most vulnerable to climate change) and on poverty eradication. Strengthening local and national capacities can support this process. The development of new technologies must also support local development.

The IPCC's Mission The Intergovernmental Panel on Climate Change is the international body responsible for assessing scientific knowledge related to climate change. Since 1988, the IPCC has been responsible for producing reports summarizing the current state of scientific knowledge on climate change in general (Assessment Reports) and on more specific topics (Special Reports). It is also responsible for providing information on options for mitigating and adapting to climate change. Each report is produced by several hundred selected volunteer scientific experts who base their work on a review of several thousand scientific articles.[1]Permafrost (officially known as “pergélisol” in French) is the layer of soil that remains frozen year-round. This frozen soil contains a large amount of carbon that would be released into the atmosphere if it thaws, particularly in the form of methane. This phenomenon, which has not yet been fully quantified, could significantly exacerbate climate change.   Article written by Violaine Lepousez and Florian Gallo