Burning of fossil fuels

The correct option is increases greenhouse gases.

To understand why this is the correct answer, let us break down the chemical and environmental processes involved in burning fossil fuels:
1. Composition of Fossil Fuels: Fossil fuels, such as coal, oil (petroleum), and natural gas, are primarily composed of hydrocarbons (organic compounds made entirely of hydrogen and carbon atoms).
2. Combustion Process: When these fuels are burned for energy, they undergo a chemical reaction called combustion. During combustion, the hydrocarbons react with oxygen from the air. The carbon atoms in the fuel combine with oxygen to form carbon dioxide, while the hydrogen atoms combine with oxygen to form water vapor.

The general combustion reaction can be represented as:
$\text{Hydrocarbon}+O_2\Rightarrow {\mathrm{CO}}_2+H_{2}O+\text{Energy}$

3. Role of Carbon Dioxide: Carbon dioxide (${\mathrm{CO}}_2$) is a major greenhouse gas. Greenhouse gases absorb and emit infrared radiation, trapping heat within the Earth's atmosphere (the greenhouse effect).
4. Environmental Impact: Because modern industrial society burns massive quantities of fossil fuels for electricity, heating, and transportation, this process releases enormous amounts of carbon dioxide into the atmosphere, directly increasing the concentration of greenhouse gases globally.