Pollution—both natural and man-made—has numerous, often complex effects on the weather. Air pollutants, for instance, can cause acid rain, and pollution that destroys the ozone layer can lead to health risks to people and even wipe out species. Many scientists believe that human-generated pollution is causing climate change, which affects weather patterns on a global scale. While some pollutants, such as gases from volcanic eruptions, can have harmful consequences, many meteorologists environmentalists, and climatologists fear that human activity is having a much bigger, negative impact on the weather and our health than anything currently occurring from natural sources.