Noise Pollution

Sound is energy moving as pressure waves, and like light, it spreads out and loses intensity as it travels away from its source. We measure that intensity in decibels, but the decibel scale is logarithmic, not linear. Each increase of 10 decibels represents a tenfold increase in actual sound intensity. So the jump from 50 to 60 decibels is not a small step up, it is ten times more intense, and a jump from 50 to 70 decibels is a hundredfold increase. This matters for pollution because sources like ships, highways, and airports can push ambient noise up by what sounds like a modest number of decibels but is actually a massive increase in acoustic energy.

For wildlife, this matters most through communication. Many marine mammals, whales especially, rely on low frequency sound to find mates, locate food, and coordinate over huge distances underwater, where sound travels far faster and farther than in air. Shipping traffic raises the background noise level across entire ocean basins. As that background rises, an animal's effective communication range shrinks, because its call has to stand out above a louder floor of noise. Doubling shipping noise does not just make things twice as hard; given the logarithmic scale, it can shrink usable communication range dramatically, forcing animals to call louder, call more often, or abandon an area altogether.

This topic closes out the unit on atmospheric and environmental pollution by shifting from chemical pollutants to physical energy as a pollutant. Like smog or acid deposition, noise pollution is a byproduct of transportation and industry, and its impact depends on dose, distance, and the sensitivity of the receiver, the same logic used throughout the unit.