Volcanic eruptions can affect the climate of the whole planet, not just the area around the volcano. When a large eruption sends sulphur gas high into the _____, the gas forms tiny droplets that reflect sunlight back into space. After one major eruption in nineteen ninety-one, average global _____ fell by about half a degree for more than a year, and some regions had unusually cool _____. These effects are _____, however, because the droplets gradually fall out of the atmosphere within two or three years. Scientists use such events to test their climate models.