A greenhouse gas is a gas that absorbs and emits radiant energy within the thermal infrared range. Greenhouse gases cause the greenhouse effect on planets. The primary greenhouse gases in Earth’s atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone. Wikipedia
Greenhouse gases cause warming on the planet, because they trap heat and prevent radiation to space. The main causes of greenhouse gases are human activities, in particular the burning of oil, coal and also the burning of forests and woodlands to open up farmland. Intensive farming also has a big part to play, as domestic cattle emit a huge amount of methane. An increasing amount of fires are caused by extreme heat and dryness, thus creating huge fires sparked by lightning, as in the California and Australian fires of 2019 and 2020.