‘Planetary climate and habitability’ studies planetary climate, particularly the way an atmosphere affects temperature and a planet's habitability. The entire temperature profile, from the planet's centre to the tenuous outer reaches of its atmosphere (if it has one), is of importance. Real atmospheres are never completely transparent to the infrared radiation which seeks to escape to space. Gases which are good absorbers of infrared radiation act as planetary insulation. This is the greenhouse effect, and gases that are good infrared absorbers are called greenhouse gases; carbon dioxide is an important greenhouse gas for Earth.