In this article, I’m going to explain what is the climate change and especially what is the main phenomenon at its origin: the greenhouse effect.

There is a natural greenhouse effect which keeps the average surface temperature on Earth at around 15°C. Without it, we would be like on Mars, with a very thin atmosphere, almost all the CO2 on the ground and an average temperature of -50°C. On the contrary, if there is too much greenhouse effect, we would be like on Venus, with a thick atmosphere containing 96% of CO2 and an average temperature of +420°C.

But who is responsible for this natural greenhouse effect? Carbon dioxyde (CO2) of course, water (H2O) and to a lesser extent, methane (CH4), are responsible of greenhouse effect since the formation of Earth 4 billion years ago.

How does it works? Well, it’s a story of energy. The climate system is subject to the first law of thermodynamics, which states that during any transformation, energy is conserved. So, the energy is brought to the Earth via solar radiation. About a third of this energy is reflected by the mirrors which are polar and arid deserts. The remaining two thirds are absorbed by the surface, which results in the evaporation of water from the oceana and infrared radiation from the ground. As the atmosphere is opaque to this infrared radiation, it will also want to put itself in an energetic balance and will therefore re-radiate infrared radiation in all directions. Except that the more opaque the atmosphere is said to be, the less radiation escapes and the hotter it gets.

A greenhouse gas is a gas that has absorption lines in the earth’s infrared, i.e. it is capable of absorbing the earth’s radiation and retransmitting it in all directions. So some of it flies off into space, but much of it is redirected towards the Earth’s surface. So the more greenhouse gases there are in the atmosphere, the more global warming there is.

Other consequences come from the difference in the temperature gradient. The higher you are in the atmosphere, the colder the air is. However, greenhouse gases cause the lower layers (the troposphere) to warm up and thus cause a higher temperature gradient between the top and bottom of the atmospheric layer. As a result, extreme phenomena that originate in convective movements are amplified, such as hurricanes, storms and tornadoes.

The problem is that human activities are responsible for releasing into the atmosphere more of the natural gases like CO2, methane, nitrous oxide (N2O) and ozone (O3), but they are also adding industrial gases into the atmosphere which also have a greenhouse effects.