Final answer:
The Earth's atmosphere warms our planet mainly through the greenhouse effect by absorbing and re-emitting infrared radiation, which is generally more than the direct absorption of solar radiation by the Earth's surface. Greenhouse gases are responsible for an essential temperature increase, making the planet hospitable for life.
Step-by-step explanation:
The Earth's atmosphere plays a crucial role in the balance of energy transfer from the Sun to our planet. When solar radiation reaches Earth, some is absorbed directly by the surface while other portions are reflected back or re-radiated in the form of longer-wavelength infrared radiation.
The greenhouse effect comes into play as greenhouse gases like carbon dioxide (CO₂) and water vapor (H₂O) absorb this infrared radiation. The absorbed energy is then re-emitted in all directions, warming the Earth's surface and lower atmosphere. This re-radiation of heat back to Earth's surface is generally more than the direct absorption of radiation from the sun, contributing to maintaining a livable climate for life as we know it.
The average emissivity (e) of Earth is about 0.65 which affects the calculation of the energy balance. Clouds can reflect more solar radiation back into space, creating a negative feedback loop that moderates temperatures. But primarily, the greenhouse gases increase Earth's surface temperature by about 40°C by trapping heat within the atmosphere, akin to the function of glass in a greenhouse. This warming effect is essential for maintaining the temperatures that sustain life.