20 NOV 2018

Heat waves, torrential rains, violent hurricanes, these events are more and more frequent and only the beginning of the climate change which today seems inevitable. Yet, a report by the Intergovernmental Panel on Climate Change (IPCC)* released in October 2018 suggests that there is still a tenuous possibility for action to limit global warming. Two experts from Sorbonne University, Professor Hervé Le Treut, climatologist and director of the Pierre-Simon Laplace Institute (IPSL) and Luc Abbadie, professor of ecology and director of the Institute of Ecology and Environmental Sciences (IEES), shed light on the complex issue of climate change.

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Maintaining the global temperature below 1.5°C will only be possible with radical transformations © Shutterstock

Climate change, a slow and irreversible process

Today at + 1° C, the globe’s temperature increase is a slow and discreet process. It takes time for the atmosphere and the ocean to warm up. This is why the major consequences of this climate change are not yet visible.

The accumulation of greenhouse gases (GHG) that have been emitted in the atmosphere during the last decades has resulted in the current phenomena of droughts, hurricanes, floods and other extreme weather. In fact, these are only the first symptoms that confirm the diagnosis made since the 1970s or 1980s by the climate models. But true climate fever will happen, according to experts, only in a few decades.

This slow change is largely unavoidable. The annual quantity of C02 released into the atmosphere has increased tenfold since 1950. Since C02 remains in the atmosphere for a century, the tons of carbon released accumulate each year in increasing numbers.

“We cannot change what will happen in 20 or 30 years. The problem of climate change is cumulative and irreversible", says Hervé Le Treut.

With a population that is growing faster and faster to reach 9 billion people on Earth in a few decades, the problem is only getting worse and more complex over time.

What does 0.5° C difference mean in global warming?

In the 2009 Copenhagen negotiations, countries adopted the goal of maintaining a rise in global average temperature below 2°C compared to the pre-industrial era. Beyond this threshold, the risks of global warming increase considerably. Six years later, at the Paris Summit, the most vulnerable countries facing climate change requested a report to the IPCC on keeping the temperature below a threshold of 1.5°C in order to set international targets that take into account the most precarious situations.

The major scientific contribution of this IPCC report, published in October 2018, is to understand what 0.5°C represents in terms of the impact on the planet and to study what this means in terms of the objectives to be achieved.

Consequences of global warming at 1.5 ° C or 2°C




Rising sea level by 2100

From 26 to 77 cm

10 cm more

Complete melting of Arctic sea ice in summer 

Once a century

Once a decade

Loss of coral reefs

70 to 90%

Up to 99%

Heat waves

Warmer 3 ° C

Warmer 4 ° C

Torrential rain


Higher risk

Loss of biodiversity

% vertebrates, 6% insects, 8% plants

8% of vertebrates, 18% of insects, 
16% of plants

Cereal crops


Decreased yield, particularly in sub-Saharan Africa, South-East Asia and Latin America


Reduction of 1.5 million tonnes per year

Reduction of 3 million tons per year

Unprecedented transitions in a global approach to the climate problem

Keeping the global temperature below 1.5°C would be possible, according to the IPCC, at the cost of radical changes. In fact, to meet this goal, global GHG emissions would have to drop well before 2030 and disappear completely in 2050, which, according to the experts, seems unrealistic.

Before implementing radical solutions, it is necessary, according to Luc Abbadie and Hervé Le Treut, to take the time to consider the issue of climate change in its entirety. By acting urgently without taking into account the complexity of the problem, "the risk is to generate solutions that can represent real ecological disasters,” says Luc Abbadie. “Miracle solutions do not exist. We have a lot of problems that we have to deal with systemically."

Thus, to reduce the amount of CO2 in the atmosphere, one of the solutions advocated by the IPCC is to use negative emission technologies. One technique involves recapturing atmospheric CO2 through photosynthesis and increasing forest areas. However, this reforestation is in direct conflict with the future extension of agricultural areas needed to cope with the 50% increase in food needs by 2050.

"We are confronted with a climate problem, but also with social, demographic and political problems," adds Hervé Le Treut. “We will not be able to do everything: preserve biodiversity, totally stop GHGs, maintain social peace. The future ahead is a future of choice and arbitration. We will be forced to compromise between social, ecological, climatic and other risks."

Consider solutions at different scales

Because the climate problem is happening simultaneously at very different scales, the responses must be considered at different levels.

“As the political system is globalized, we need large international meetings to reflect together on the issues of the planet as well as a national scale to defend our interests as a country,” says Hervé Le Treut. “It is also at the national level that the production of energy is reflected. At the same time, the regional scale is essential because it is the source of direct impacts of climate change, as well as some of the solutions."

According to Hervé Le Treut, it is at this local level that urbanization, housing, agriculture and transportation, which are major issues in reducing GHGs. This is where it is possible to propose concrete solutions and to make choices according to the specificities of each territory.

Finally, for Luc Abbadie reminds us not to forget the participation of ordinary citizens: "each of us has a responsibility to fight, at our own level, against waste, especially food, and make choices in lifestyle."

developpement durable
The transition required by climate change requires new knowledge © Shutterstock

An opportunity to innovate

While individual awareness of climate change has increased significantly in recent years, there is still a need to raise awareness and educate the public. This is where universities have an important role to play, that of enlightening the general public about the complexity of the choices to be discussed and to be made.

"Action cannot happen without a global understanding. It is our duty as academics to evaluate solutions and disseminate knowledge so that society can grasp it and move the debate forward," says Abbadie. “We have an important responsibility: to educate the citizens and decision-makers of tomorrow."

According to Hervé Le Treut, it is also necessary to develop continuity between research and applications in society, to make research operational. The transition necessitated by climate change requires new knowledge. Academics open scientific avenues for communicating and promoting results to make an effective contribution to environmental transition.

This is also what the Institute of Environmental Transition at Sorbonne University proposes. Based on the University’s 54 laboratories and about 2,000 researchers, professors, PhD students and engineers directly concerned, this Institute is designed to be a platform for interactions between science and society. Through interdisciplinary approaches, the ITE will identify, enrich and articulate the different facets of the transition to ensure that the scientific innovation produced on a daily basis in the laboratories leads to operational solutions for citizens.

As a result, the crisis caused by climate change can also be seen as an opportunity to innovate.

"If France becomes a leader and drives the change, it will become normative and competitive. Innovation to combat climate change can be a powerful and strategic development direction for the country. It is an invitation to build different things, to rethink the system completely," says Abbadie.

* Established in 1988, the IPCC assesses the state of scientific, technical and socio-economic knowledge of climate change, and its causes and impacts. It identifies ways to limit the extent of global warming and the opportunities to adapt to expected changes.