4. Energy and the greenhouse effect

If the greenhouse effect did not exist, the average temperature at the Earth's surface would be – 18°C. Water would be in the form of ice, and life could not exist as we know it. Fortunately, the natural greenhouse effect, which results from the presence of gases in small quantities in the atmosphere such as water vapour or carbon dioxide (CO ₂ ), raises the average temperature by 33°C. It is therefore 15°C, which makes our planet habitable for life as we know it. While the natural greenhouse effect is essential, its slight increase due to human activities is a cause for concern. Much of this increase comes from the use of fossil fuels for energy purposes. CO ₂ is the gas with the greatest contribution to the man-made greenhouse effect, but other gases also have a harmful effect, such as methane,...