Greenhouse effect

Greenhouse effect and mechanisms of climate change

When Earth is heated up by the sun, it returns some of the radiation it receives to the atmosphere. A portion of these rays is retained by the greenhouse gases (carbon dioxide, methane, etc.) and radiates downwards, back to the Earth, which warms it up. This phenomenon exists since the atmosphere itself appeared.

The climate naturally varies since the formation of Earth. What is different today is the pace of this change. Through its activities, humans have disrupted this natural mechanism by producing more greenhouse gases. The burning of oil and gas, deforestation, intensive agriculture, etc., are the direct effects of the industrial revolution. Gases accumulate in the atmosphere at a level well above the natural level. The gases concerned are mainly carbon dioxide (it is present in quantity 1.5 times larger than in the 19th century) and methane.

Effects of greenhouse gases increase

The increase in greenhouse gases results in:

  • Rise in temperature: Earth temperature has already increased by 0.8 ° C since the end of the 19th century and droughts are more frequent and affect more territories than before. If the CO2 concentration doubles by 2100, the temperature of the Earth will have increased by 1.5 to 4.5 ° C.
  • Sea level rise: as glaciers and polar ice caps melt and recede, and as the oceans expand because they are warmer than usual, ocean levels rise by about 3.3 mm per year, and this sea level rise is increasing. In the worst-case scenario, sea level could have risen by one meter in 2100. Entire territories such as Kiribati or the Maldives will then gradually disappear.
  • Increased precipitation in the northern hemisphere and droughts in the southern hemisphere and regions already prone to drought: droughts will be longer and more frequent, and the flow of rivers will be reduced; biodiversity will be hit hard and humans will have trouble cooling thermal and nuclear power plants, which can lead to a significant decline in electricity production.
  • Ocean acidification: more CO2 than usual dissolves in surface water and makes it more acidic. The rapidity of the phenomenon prevents scientists from being able to predict its effects on living organisms: some shellfish and plankton, bases of the food chain, may not be able to adapt, and their disappearance could have an impact on the whole world food chain, including humans.

In terms of climate change, there are strong regional disparities, but it trends towards warming up, as shown in the map below. After numerous studies, NASA and NOAA have concluded that 2016 has been the hottest year on the planet since the beginning of the temperature surveys in 1880.

Source : Serge Planton, Meteo France, extract from the IPCC 2015 report

What about El Niño?

No talking about climate change without talking about El Niño. El Niño is an oceanic and atmospheric phenomenon that affects the global climate - tropical storms, rainfall - and can add to the effects of climate change. This natural cyclical phenomenon, which returns every three to seven years, warms the waters of the equatorial Pacific, along the coasts of Ecuador and Peru, and inverts the Pacific trade winds. It causes major weather changes on a global scale.

There is no consensus on whether climate change will have any influence on the occurrence, strength or duration of El Niño events. Conversely, El Niño itself cannot account for global change. For example, we observed heat records in 2014, a year without El Niño.

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