The greenhouse effect occurs when the thermal energy reflected by the Earth to the atmosphere (from the sun) is absorbed by the greenhouse gases on it. Due to this, the radiation goes again to the Earth and elevates the temperature of the lowest part of the atmosphere and of the surface of the Earth. It was discovered by Joseph Fourier in 1824. Earth's greenhouse effect is a natural process, but the human activity has increase the air pollution making the greenhouse effect too intense provoking global warming.