The atmosphere around the earth.
This atmosphere has seen an increase in temperature over the last several years.
This process of global warming is called global warming.
The sun's rays pass through the atmosphere and reach the earth's surface directly.
First warms the earth's surface.
Then the atmosphere slowly warms up.
When the sun's rays are reflected from the earth's surface and pass through the atmosphere, the carbon dioxide in the atmosphere absorbs the long-wavelength "infrared" rays and reflects them back to the earth.
As a result the earth and the atmosphere get warmer.
This effect is called the greenhouse effect.
Carbon dioxide gas having such an effect is called greenhouse gas.
Other greenhouse gases are methane, nitrous oxide, chlorofluorocarbons, etc.