Global warming happens when the concentration of certain gases, known as greenhouse gases (GHG) increases in the atmosphere because of human and industrial activity, especially CO2, and chlorofluorocarbons (CFCs). The main GHG is carbon dioxide, which is mostly produced as a bi-product of the use of coal, petroleum and gas as well as by deforestation and forest fires.
Ongezeko la joto duniani husababishwa na ongezeko la aina Fulani ya gesi ambayo imepewa jina la gesi ya nyumba ya kijani (Greenhouse) au GHG kutokana na shughuli mbalimbali za watu na pia viwanda, hasa zile za CO2 na CFC. Gesi kubwa ya GHG ni carbon dioxide ambayo hutokana na matumizi ya mkaa, petroli na gesi pamoja na kukata na kuangamiza misitu.