A fifth factor—the so-called grasshopper effect—occurs when volatile air pollutants are transported by evaporation and winds from tropical and temperate areas through the atmosphere to the earth’s polar areas, where they are deposited. This happens mostly during winter. It explains why, for decades, pilots have reported seeing dense layers of reddish-brown haze over the Arctic. It also explains why polar bears, sharks, and other top carnivores and native peoples in remote arctic areas have high levels of toxic pollutants in their bodies