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.
The increase in greenhouse gases results in:
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
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 bserved heat records in 2014, a year without El Niño.