The extreme greenhouse effect on Venus is primarily caused by its thick atmosphere, which is rich in carbon dioxide. This dense atmosphere traps heat from the Sun, leading to surface temperatures high enough to melt lead. Unlike Earth, where heat can escape into space, Venus's atmosphere is about 90 times denser and composed almost entirely of carbon dioxide, a potent greenhouse gas. This prevents heat from radiating away from the surface, creating a runaway greenhouse effect. Additionally, the presence of clouds of sulfuric acid amplifies this effect by further trapping heat.