The correct answer is option 1: increase in the content of carbon dioxide in the atmosphere. This is because carbon dioxide is a greenhouse gas, which means it has the ability to trap heat in the atmosphere. When the concentration of carbon dioxide increases, more heat is trapped, leading to an increase in global temperature. This phenomenon is known as the greenhouse effect, and it is the main cause of global climatic change.

Option 2, emissions of industrial gases, is closely related to option 1. Industrial gases such as methane and nitrous oxide also contribute to the greenhouse effect and global warming.

Option 3, adding of dust, may have some localized effects on climate, but it is not a major driver of global climatic change.

Option 4, changes in plant cover, can affect local climate conditions, but it is not the primary cause of global climatic change.

Overall, option 1 accurately identifies the main cause of global climatic change.