Final answer:
Venus's surface is much hotter than Earth's due to a runaway greenhouse effect caused by its thick CO₂ atmosphere, which traps heat and prevents it from escaping back into space. This demonstrates the impact of atmospheric composition on a planet's temperature and relates to global warming concerns on Earth.
Step-by-step explanation:
The primary reason for the actual difference in surface temperature between Venus and Earth is the greenhouse effect. Venus has an extraordinarily high concentration of carbon dioxide (CO₂) in its atmosphere, nearly a million times more than Earth. This massive amount of CO₂ creates a runaway greenhouse effect that traps infrared radiation, warming the surface to extremely high temperatures.
The energy balance on Venus is achieved only when it radiates back into space as much energy as it receives from the Sun, at a much higher temperature due to the strong greenhouse insulation. This illustrates the importance of atmospheric composition in terms of a planet's surface temperature and is relevant to concerns about global warming on Earth today because it underscores the potential for an intensified greenhouse effect to significantly increase surface temperatures.