Climate change, the facts

To fully grasp the issues associated with climate change, it is first necessary to understand the greenhouse effect. This natural phenomenon played an essential role in the development of life on Earth because, without it, temperatures on the planet's surface would be constantly negative (-19°C on average, compared to +15°C currently) .1

Different elements compose our atmosphere, mainly nitrogen and oxygen, but also so-called greenhouse gases (GHGs) such as carbon dioxide (CO2) or methane (CH4). In practice, when sunlight reaches the Earth's surface, infrared radiations are re-emitted toward the atmosphere and space. The proportion of infrareds (and therefore heat) absorbed by the atmosphere is related to its concentration in greenhouse gases.
Without the greenhouse effect, solar energy arriving at the Earth's surface is reflected back to space as infrared 2
With greenhouse effect, part of the solar energy is retained as infrared on the Earth's surface
The higher the concentration of greenhouse gases, the more solar energy is absorbed, and the higher the temperatures.

The 6 Greenhouse Gases (GHGs) and their contribution to global warming

The main GHGs present in the atmosphere are, in addition to water vapour (H2O): carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), as well as industrial gases: hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphur hexafluoride (SF6). Each of these gases has its own characteristics and contributes in a differentiated way to climate change. Experts from the Intergovernmental Panel on Climate Change (IPCC) have defined an indicator, the Global Warming Potential (GWP), to express the effect of these GHGs in a normalised value. This is referred to as carbon dioxide equivalent - CO2e.

The greenhouse effect attributed to CO2 is set at 1 and that of the other gases is quantified in relation as CO2e (at equal emission levels). The GWPs of these different gases vary according to, among other factors, their lifespan in the atmosphere and their inherent warming power.

Greenhouse gas GWP equivalence table

 

Gas

Lifespan (years)

GWP at various horizons

20 years

100 years

C02

Variable – over 100y

1

1

CH4

12

84

28

N20

121

264

265

NF3

500

12800

16100

SF6

3200

17500

23500

CF4

50000

8800

6630

HFC-22

12

5280

1760

 

Anthropogenic GHG emissions

Since the industrial revolution, so-called "anthropogenic" greenhouse gas emissions, i.e. associated with human activities, grew at a high and sustained rate. These emissions are mainly linked to the production and consumption of fossil fuels (coal, gas, oil) in transports, buildings, the agriculture, the industry... as well as the destruction of carbon "sinks", in particular through deforestation. In short, we are talking here about our production and consumption patterns.

Our GHG emissions reinforce the greenhouse effect and produce a gradual warming of temperatures. This warming, even if it may seem modest at first sight (close to 1°C on average since the middle of the 19th century, but with strong regional disparities), generates major disruptions to our climate system: changes in precipitation patterns, ocean currents, rising ocean and sea levels due to the melting of land ice and the thermal expansion of water, extreme weather events, heat waves, etc.

This climate disruption in turn has a significant impact on our ecosystems (biodiversity, natural resources, etc.) and our societies through multiple consequences on health, food production, infrastructures, economic activities such as tourism or transport, migrations, etc. Today, and in view of the intensification of the phenomenon, it has become urgent to act by drastically reducing our greenhouse gas emissions and by adapting as best as possible to the consequences that have become inevitable.

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