Global warming isn't just restricted to Earth. Both our neighbouring planets, Venus and Mars, are warmed by the effects of greenhouse gases in their atmospheres. In fact, from comparing these three rocky worlds, scientists have gained an invaluable insight into how the quantity of greenhouse gases in a planet's atmosphere can radically affect the climate and surface conditions – conditions which are crucial for life.
On Earth, the majority of carbon lies not in the atmosphere, but in the oceans and rocks. Just 0.00035% of Earth's atmosphere is made of carbon dioxide. However, this carbon dioxide, along with water vapour and other small amounts of greenhouse gasses, is enough to raise the average surface temperature of Earth by around 30°C. Without it, Earth would be frozen.
By comparison, the atmosphere of Venus is composed of 96% carbon dioxide (260,000 times more than Earth) and is much denser, containing around 100 times more gas than Earth's. The thick dense carbon dioxide atmosphere on Venus has led to a 'run away' greenhouse effect, with surface temperatures soaring to around 460°C, hot enough to melt lead, and three times greater than otherwise expected.
Mars too has an atmosphere made mainly of carbon dioxide (95%), but there the atmosphere is over 100 times thinner than Earth's. So even though, like Venus, the Martian atmosphere is almost solely made of carbon dioxide, it's actually so thin that the effect of greenhouse warming lifts the global temperature by just 6°C.