Despite orbiting closer to the Sun, Venus actually absorbs less sunlight than Earth. Without its runaway greenhouse effect, the 464°C (867°F) furnace wouldn't become Earth-like—it would freeze.
The physics behind this counterintuitive outcome relies on albedo, the measure of how much sunlight a planet reflects. Venus is blanketed in thick clouds of sulfuric acid that act like a giant mirror, reflecting about 75% of incoming solar radiation back into space. Earth, by comparison, reflects only about 30%. Venus is only hot because its atmosphere, which is 96% carbon dioxide, aggressively traps the small fraction of heat that manages to penetrate the clouds.
If the greenhouse effect were magically eliminated while leaving those highly reflective clouds in place, Venus’s surface temperature would plummet. Its average temperature would drop to around -43°C (-45°F), leaving the entire planet far colder than Earth.
A different scenario emerges if Venus were given an Earth-like atmosphere. If the thick carbon dioxide and sulfuric acid were replaced by nitrogen, oxygen, and water clouds, Venus would match Earth's 30% albedo. At 0.72 astronomical units from the Sun, Venus receives about 1.91 times more solar irradiance than Earth. Absorbing 70% of that intense sunlight would push its baseline temperature to roughly 26°C (79°F).
Adding a moderate, Earth-level greenhouse effect (which warms Earth by about 33°C) would bring Venus's average surface temperature to about 59°C (138°F). This is hotter than the highest temperature ever recorded in Death Valley, applied as a global average. At these temperatures, oceans would rapidly evaporate, filling the atmosphere with water vapor—a potent greenhouse gas that would trigger a runaway greenhouse effect all over again.
Without its massive carbon dioxide atmosphere, Venus would technically sit much closer to Earth's temperatures than its current extreme. But its position in the solar system guarantees it is just slightly too close to the Sun to maintain liquid water long-term.