A major volcanic eruption or asteroid impact could block sunlight, causing a sudden global cooling sometimes called a 'volcanic winter.'

When volcanoes erupt massively, they send ash and gases high into the atmosphere. These particles can block sunlight for months or years, cooling the planet. This effect can damage crops and disrupt ecosystems. Similarly, a large asteroid hitting Earth could throw up dust that blocks sunlight. These events are rare but have happened before, like the eruption of Mount Tambora in 1815, which caused the 'Year Without a Summer.'