Final answer:
The Earth's temperature is maintained at habitable levels due to the greenhouse effect, which is influenced by greenhouse gases like H₂O and CO₂ trapping heat in the atmosphere. The Earth's emissivity and variable cloud coverage play roles in the energy balance that determines the temperature. Without the greenhouse effect, Earth's average temperature would be significantly lower, making it inhospitable for most life forms.
Step-by-step explanation:
The temperature of the Earth's atmosphere is significantly influenced by the greenhouse effect, which is a natural phenomenon that keeps the Earth's surface at habitable temperatures. Without the presence of greenhouse gases such as water vapor (H₂O) and carbon dioxide (CO₂), the energy from the Sun would be lost to space, and the Earth's average temperature would plummet to around -18°C, rather than the current average of 15°C. The greenhouse gases trap heat within the atmosphere, preventing it from escaping into space and thus warming the Earth.
The Earth's emissivity (e), which is around 0.65, plays a critical role in the energy balance and temperature regulation. However, this is complicated by the variability in highly reflective cloud coverage, which can reflect radiation back to the surface. The greenhouse effect is enhanced by the Earth's atmospheric composition, where water vapor is responsible for raising the Earth's temperature by approximately 20°C and CO₂ adds another 8°C, with other gases contributing as well.
Changes in atmospheric conditions, including cloud formation and the concentration of greenhouse gases, are key drivers of the Earth's climate. Higher temperatures result in more water being evaporated, forming more clouds, which then reflect radiation back to space and can potentially lower temperatures. Nonetheless, the current levels of greenhouse gases are what enable the Earth to maintain an average surface temperature that is suitable for the plethora of life forms that inhabit it.