CBSE Class 10 Science 2017 · Paper 31/2/1 · Question 6

Fossil fuels such as coal, petroleum and natural gas are rich in carbon. When they are burnt, the carbon forms carbon dioxide ($\text{C}+{\text{O}}_2\to {\text{CO}}_2$), which is released into the atmosphere. Carbon dioxide is a greenhouse gas: it lets sunlight through but absorbs part of the heat radiated by the Earth's surface and sends some of it back, so less heat escapes to space. As burning keeps adding carbon dioxide to the air, more heat is trapped and the average temperature of the Earth rises. This is global warming, so burning fossil fuels is a cause of it.