1. How can climate change be measured? What does this limit that must not be exceeded mean?
Climate change is often measured by the increase in global warming, currently estimated at +1.25°C since the pre-industrial era. This phenomenon is closely linked to the increase in greenhouse gases (GHGs), particularly carbon dioxide (CO2), whose concentration has risen from 280 ppm* to 420 ppm today, a level at which the impacts are already being felt strongly. It is therefore imperative not only to slow down the current increase in this concentration, but also to initiate a gradual decline in order to return to a safe climate zone. It is crucial to get as close as possible to the target of keeping global warming below 2°C, as set at COP21 by the Paris Agreements. Without this, extreme weather events will continue to increase in intensity and frequency, with increasingly serious local consequences. Every fraction of a degree avoided can make a real difference, explains Olivier Boucher.
*This number indicates the number of carbon dioxide molecules present in one million air molecules (parts per million or ppm).
2. What are the scenarios for change and why are we talking about carbon neutrality?
Scientists are developing various GHG emission trajectories based on scenarios for global socio-economic change until the end of the century. These different trajectories, which vary in their degree of optimism, are used to project climate change. Currently, we are heading towards a warming of 2.5°C to 2.7°C by 2100, well above the 1.5°C threshold recommended by the Paris Agreement. To stabilise this trend, carbon neutrality is necessary. This involves drastically reducing GHG emissions so that the residual amount emitted by human activities is equal to the amount removed from the atmosphere by additional carbon sinks. These additional sinks should not be confused with natural sinks, which already absorb nearly half of our CO2 emissions. ‘We must therefore offset our residual emissions, particularly CO2, with additional sinks.’ These carbon sinks can be natural (managed forests, agricultural soils) or technological (carbon capture and storage). This transition requires concerted efforts at all levels.
3. What are the concrete impacts of climate change?
The consequences of global warming are many and varied.
- Rising temperatures: continents and high latitudes are warming faster, with an acceleration in the UK compared to the global average
- Extreme weather events: heat waves are becoming longer, more frequent and more intense
- Disruption of the water cycle: increased droughts in certain regions such as the Mediterranean basin, while others are experiencing flooding due to torrential rains
- Impacts on biodiversity: the combination of climate change, deforestation and ocean acidification poses a major threat to ecosystems
All regions are affected by global warming, but not in the same way. The effects vary depending on local characteristics. Certain geographical features increase vulnerability: a very obvious example is coastal areas, which are particularly exposed to sea level rise and erosion. Other areas, such as the south-eastern departments of France, may face an intensification of Mediterranean-type episodes (such as the cévenol). Finally, the most vulnerable societies – due to poverty, poor organisation or a lack of effective governance – also suffer more severe consequences.
A Cevennes storm is a phenomenon of intense thunderstorms and rainfall in south-eastern France, from the Cévennes to the Alps. It takes its name from the Cévennes massif, where rain and thunderstorms from the Mediterranean come to rest. The phenomenon occurs 3 to 6 times a year, mainly in autumn, and these episodes are intensifying with climate change. The storm rarely lasts more than four days (Source: Météo France).
This imbalance spreads throughout the food chain. By affecting phytoplankton, the first link in the ocean’s trophic network (food chains), the entire foundation of marine resources can be compromised. The fish we consume depend directly on it.
Moreover, coral reefs, which are also highly sensitive to acidification, provide numerous ecosystem services. They are vital for tourism but also for coastal protection: they shield our shores from coastal flooding caused by major tropical cyclones. The degradation of reefs could therefore weaken coastal communities and the blue economy
Finally, this phenomenon is interconnected with other planetary boundaries, such as those related to the nitrogen and phosphorus cycles. These nutrients, mainly from fertilisers, can lead to algal blooms and dead zones by depleting coastal waters of oxygen.
4. How does climate change interact with other planetary boundaries?
Climate change interacts strongly with other global limits, and there are many examples of this. Regions facing other environmental pressures, such as unsustainable agriculture or deforestation, may not only see their ecosystems degrade and become more sensitive to climate change, but may also become major sources of greenhouse gas emissions. Global warming also alters the hydrological cycle, intensifying evaporation and disrupting the distribution of rainfall, thereby affecting water resources. The absorption of atmospheric CO₂ by the oceans leads to a drop in the pH of the water, harming many marine species. Shellfish, coral and plankton find it harder to form their skeletons or shells, disrupting the entire oceanic food chain. The climate is exacerbating the collapse of certain species, particularly by disrupting their habitats or reproduction cycles.
Another approach is to reduce biological pressures, for example by removing predators such as starfish, which threaten weakened corals. From a chemical point of view, trials have been carried out on small reefs with the addition of alkaline material (bases) to neutralise acidification and encourage calcification. Initial results indicate that corals calcify better under these conditions.
Finally, nature-based solutions are also being considered, such as the restoration of mangroves, which contribute to coastal resilience by protecting human populations from extreme events.
5. What are the levers for sustainable change?
When it comes to global warming, there is no miracle solution. Ideally, we need to use all the levers at our disposal and activate them simultaneously.
Mitigation
Reducing greenhouse gas emissions is essential if we are to limit global warming. This requires ambitious climate policies, energy transitions and global efforts.
Adaptation
Adaptation involves minimising the inevitable impacts of climate change. Solutions include water resource management, infrastructure resilience and sustainable agricultural practices.
Businesses have a key role to play in the fight against climate change. Here are the key levers for action:
Carbon footprint: identify direct and indirect emissions to reduce them more effectively
Scope 3*: act on the supply chain, encourage digital sobriety and design products that are more respectful of the environment
Non-financial reporting: transparency on emissions becomes a competitive advantage to attract talent, win over consumers and achieve economic success.
Climate change is not inevitable, but it requires immediate and concerted action. Mitigation and adaptation strategies are complementary, as are individual, technological and financial efforts. By redirecting investment, adopting ambitious climate policies and relying on nature-based solutions, we can build a resilient and sustainable future.
*Scopes 1, 2 and 3 represent the different major categories of greenhouse gas emissions from an organisation. Scope 3 generally includes the vast majority of indirect emissions linked to a company’s activities.
Olivier Boucher is a French climatologist, director of research at the CNRS and deputy director of the Institut Pierre-Simon Laplace in Paris. Lead author of IPCC Working Group 1, he is a specialist in climate modelling and climate change. His research covers methane, atmospheric particles, aircraft contrails and decarbonisation trajectories. He is working on solutions to combat climate change, such as reforestation, capturing atmospheric CO₂ via biomass and reducing non-CO₂ greenhouse gas emissions. In his view, measurement, understanding and action are essential today, but there are no ‘miracle solutions’. ‘We must act collectively by mobilising three specific levers: technological, organisational and individual levers’.
