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Greenhouse effect: definition and role in global warming – What is the greenhouse effect

What is the greenhouse effect? How is it impacted by human activities? A major risk: the runaway of the greenhouse effect.

Definition of the greenhouse effect
In terms of climate, the greenhouse effect is a natural phenomenon that contributes to the average temperature level on the surface of a planet with an atmosphere.

On Earth, 30% of solar radiation is directly returned to space under the effect of reverberation, about 20% is absorbed by the atmosphere and a little more than 50% by the earth’s crust and the oceans. The stored heat is then returned to the atmosphere by convection and in the form of infrared radiation.

That’s where the phenomenon comes in: part of this infrared radiation goes back to space, and another part is trapped by the greenhouse gases (GHGs) in the atmosphere and then sent back to the surface it heats up to a variable level depending on the concentration of GHG.

In the absence of a greenhouse effect, the average temperature (+ 15 ° C) on the surface of the planet would be much lower: -18 ° C.

The greenhouse gases naturally present in the atmosphere are mainly:

water vapor,
carbon dioxide (CO2),
ozone,
methane,
nitrous oxide.


Influence of human activity on the greenhouse effect


Since the beginning of the industrial era, the growing use of fossil fuels (coal, oil, lignite) and natural gas has resulted in additional GHG emissions that reinforce this effect. Also concerned are deforestation (less storage of CO2) and intensive livestock farming (methane emissions).

The increase in “classical” GHGs of anthropogenic origin (related to human activity) is not the only cause. The industry, in fact, releases into the atmosphere specific greenhouse gases, such as sulfur hexafluoride.

It is now undeniable that these additional GHG emissions significantly increase the natural greenhouse effect and consequently contribute to the ongoing global warming.

Greenhouse effect: the risk of runaway


As regards warming, it may seem paradoxical to speak of a “snowball effect”. However, the hypothesis of a runaway phenomenon is not excluded.

Indeed, the rise in temperatures already underway can eventually cause an excessive decrease in the reverberation, especially by melting glaciers and ice floes. In addition, the extension of arid climate zones leads to a decrease in plant biomass and thus in the natural storage of carbon. The warming of the oceans, as well as the thaw of permafrost, can also release large quantities of methane.

The combination of all these factors may accelerate the increase in the greenhouse effect until it becomes out of control. This is the challenge of global action to combat global warming, promote sustainable development and resilience.

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