Comprendre le changement climatique et ses conséquences

Commissariat général au développement durableSep 15, 2026

À cause des activités humaines et de leur utilisation d’énergies fossiles (charbon, pétrole, gaz), les émissions de gaz à effet de serre augmentent rapidement. Cela renforce l’effet de serre et réchauffe la Terre : le climat se modifie et avec lui les températures, les précipitations (pluie, neige, grêle) et les vents. 2024 a ainsi été l’année la plus chaude jamais enregistrée au niveau mondial. Si cela se traduit de façon différente selon les régions et les saisons, l’humanité fait aujourd’hui face à un bouleversement climatique, avec des conséquences déjà visibles dans de nombreux domaines.

Due to human activities and their use of fossil fuels (coal, oil, gas), greenhouse gas emissions are increasing rapidly. This intensifies the greenhouse effect and warms the Earth: the climate is changing and with it temperatures, precipitation (rain, snow, hail), and winds. 2024 was thus the hottest year ever recorded globally. While this manifests differently depending on regions and seasons, humanity is today facing a climate upheaval with already-visible consequences in many sectors.

3 chapters

What is climate change?
Greenhouse gases, main cause
• Thanks to greenhouse gases naturally present in the atmosphere (water vapor, carbon dioxide, methane…), Earth absorbs part of the energy it receives from the Sun, while the rest is reflected back into space. This natural phenomenon, called the greenhouse effect, makes life on Earth possible: without it, the planet's average temperature would indeed be freezing, around -18 °C. These gases therefore play an important role in regulating the climate. • In recent decades, the concentration of greenhouse gases in the atmosphere is increasing rapidly due to human activities and the combustion of fossil fuels (oil, natural gas, coal). This intensifies the greenhouse effect and traps a larger portion of the heat received from the Sun in the atmosphere, causing a rise in Earth's temperature: this is global warming.
Direct consequences of warming
• The consequences of climate change are multiple: changes in temperatures at Earth's surface, rising sea levels, melting snow and ice, disruption of precipitation (rain, snow, hail), and multiplication and intensification of extreme weather events (e.g., floods, droughts, hurricanes…). • Rising sea levels are primarily due to changes in the temperature of seas and oceans: as heat increases, water expands and occupies a larger volume. It is also due to the melting of land ice or freshwater-based ice (ice sheets, glaciers, etc.) as temperatures rise. • The melting of mountain glaciers, sea ice, and polar ice caps is caused by rising temperatures at Earth's surface and in seas and oceans. • Precipitation levels (rain, snow, hail) are also changing. A warmer atmosphere can carry up to 7% more humidity (and therefore water) per degree of warming, and the more humid the atmosphere, the greater the probability of rainfall. • Climate change also alters the intensity, frequency, duration, and distribution of extreme phenomena such as floods, storms, droughts and heat waves, hurricanes, tornadoes, cyclones, typhoons, wildfires…. For example, droughts will be more frequent, more intense, and longer due to increased evaporation linked to rising temperatures. • > Weather vs. climate: what's the difference? > Weather is what happens each day around us: hot or cold conditions, rain, snow, wind, etc. Climate, on the other hand, is an average of meteorological conditions over a long period (several decades). It is therefore normal to continue observing occasional cold spells: weather is by nature different each day, and this does not call into question the overall trend of climate change in the long term.
Global problem with regional effects
• Climate change is a problem affecting the entire planet. However, the level of warming and its effects manifest differently depending on each geographic area: hot or cold regions, humid or desert climates, continental or coastal areas, rural or urban, economically wealthy or poor, etc. • The increase in average global temperature compared to the pre-industrial era (period between 1850 and 1900) is already 1.1 °C. The Paris Agreement aims to keep this increase below 2 °C and ideally below 1.5 °C. This international agreement was adopted in 2015 at the 21st Conference of the Parties (COP21) of the United Nations on climate change, in Paris.
Already-felt consequences across many sectors
Warming observed in France
• In mainland France and French overseas departments, temperature increases have been particularly pronounced since the 1980s. Over the period 1959-2009, the trend is approximately +0.3 °C per decade. In 2022, the average annual temperature across the country reached 14.5 °C, making it the hottest year since measurements began in 1900, followed by 2023 (14.4 °C), 2020 (14.1 °C), 2018 (13.9 °C), and 2024 (13.9 °C). • The number of summer days (with temperatures exceeding 25 °C) has increased significantly, while frost days (with minimum temperatures below 0 °C) have decreased. In Agen, for example, there were 43 frost days per year during 1960-1970 compared to 30 during 2010-2020. Extreme rainfall in France's Mediterranean southeast is becoming increasingly intense. • In mountains, major monitored mainland glaciers have retreated 31.4 meters in 21 years. Snow cover is also declining. At Col de Porte (Chartreuse), winter snow depth during 1990-1991 and 2019-2020 is 38 cm less than during 1960-1961 and 1989-1990.
Impacts on biodiversity and agriculture
• Climate change also has consequences for water and biodiversity, as evidenced by the advance of bird migration dates, the expansion of pine processionary caterpillars, rising water temperature in Lake Geneva, increased areas affected by annual droughts in mainland France, etc. • In agriculture, grape harvest dates, an indicator of vegetation's response to climate change, occur on average 18 days earlier than 40 years ago. Corn and wheat crops are also adapting to changing environmental and climatic conditions, with an overall earlier sowing date.
Social, economic and geopolitical impacts
• More broadly, society and the economy are affected: increased climate risks (heat waves, floods, cyclones, etc.) and health risks (vector-borne diseases, etc.), economic losses (lost work days, reduced agricultural yields, lower tourism, material damage, etc.). • France could also experience the consequences of climate change in other countries. Indeed, the emergence of geopolitical crises (migration, conflicts, etc.) generated by tensions over resource access (food, water) is a risk highlighted by the IPCC and considered in international and national strategic thinking. • > The IPCC and its reports: international scientific references > Created in 1988 by the World Meteorological Organization and the United Nations Environment Programme, the IPCC (Intergovernmental Panel on Climate Change) comprises 195 member states. Its objective is to assess and synthesize the available scientific, technical, and socio-economic information on climate change. > The work of the IPCC leads to the regular publication of reports, aimed at building consensus within the scientific community while also identifying limits in knowledge or interpretation of results. Understanding the scientific basis of climate change caused by human activities enables the implementation of adaptation and mitigation strategies. • > Precise monitoring of impacts in France through ONERC > Created by the law of February 19, 2001, the National Observatory on the Effects of Global Warming (ONERC) has the main missions of collecting and disseminating information on risks linked to global warming, as well as formulating recommendations on adaptation measures to consider in order to limit the impacts of climate change. It works closely with the IPCC for this purpose. > To describe the state of the climate and its impacts across the entire French territory, ONERC has equipped itself with a panel of indicators, each associated with a phenomenon and allowing it to indicate the change over time in an objective manner.
Worrying future prospects
Warming dependent on future emissions
• The future climate is determined by greenhouse gases (GHG) already emitted into the atmosphere and by new emissions in the years to come. To predict climate warming, the IPCC relies on economic development scenarios with human societies that emit more or less GHG. These scenarios lead to temperature increases ranging from +1.4 °C to +4.4 °C globally by the end of the century compared to the pre-industrial era. • Meeting the Paris Agreement scenario (+1.5 °C by 2100) requires humanity to stop CO2 emissions within approximately 30 years and significantly reduce other GHGs. If each country's climate policies remain at their current level, global warming is expected to reach approximately +3 °C by the end of the century. Some impacts are also already irreversible. This is the case with rising sea levels, which will continue for several centuries, and polar ice melting.
Climate risks increasing rapidly
• The IPCC's work predicts that exceptional climate events (droughts, heat waves, heavy precipitation, cyclones) will be more frequent and/or more intense in the future. Globally, a drought episode that occurred on average once every ten years in 1900 could occur four times more frequently by 2100 with global warming of +4 °C. An exceptional precipitation episode (in one day) could occur two to three times more often. • Global warming of +3 °C will correspond to approximately +4 °C warming in mainland France by 2100 compared to the pre-industrial era. Temperature increases will be stronger in summer, with more frequent heat waves, particularly around the Mediterranean, in the Rhône Valley and the Garonne Valley. Extreme rainfall is also expected to increase, particularly in northern France. This will not prevent rivers from often having very low levels in summer, with water shortage situations likely to multiply throughout France. • Excessive warming will cause irreversible damage: rising oceans, biodiversity loss, etc. For example, at +2 °C warming, coral reefs will disappear even though they shelter 30% of marine biodiversity. Meanwhile, beyond a critical threshold, warming could trigger cascading events with catastrophic consequences: the collapse of ice sheets would cause sea levels to rise several meters, disruption of ocean currents would cause profound climate changes, permafrost thaw would release enormous quantities of methane and greatly increase the greenhouse effect, etc. • Impacts abroad could also have repercussions for France. Crop losses abroad, induced by climate warming, will for example affect French food supplies.

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