What effect can greenhouse gases have on climate?
Increases in greenhouse gases can increase the greenhouse effect and warm the Earth.
In order for the Earth to maintain and even temperature, it has to be in balance with the sun. That means that the amount of energy from the sun that the Earth receives has to equal the amount of energy the Earth emits into space.
Rays from the sun travel through the atmosphere, and warm the surface of the Earth. The warmed Earth releases heat that does not travel freely through the atmosphere, certain gases in the atmosphere (greenhouse gases) trap that heat. They work like the glass of a greenhouse, allowing the light of the sun to shine through but trapping the heat.
The greenhouse effect to a certain degree is natural, but the rampant increase of greenhouse gases due to human activity is not natural. The end result is we are not in balance with the sun anymore and the Earth's temperature will increase and we will have a new balance.
Ozone depletion is a serious problem but it is a different issue entirely. Greenhouse effect occurs in the troposphere, and the ozone layer is in the Stratosphere.