National Park Service has recorded sound levels at more than 600 sites across the US, including Yosemite in California, Yellowstone and Denali in Alaska. Not one was unaffected by some form of noise from human activity, be it over-flying aircraft, motorbikes, motorboats or tour buses. Fristrup’s team combined the sound levels recorded from national parks with similar data from urban settings to create a model of noise levels across the US. They predict that noise pollution is growing faster than the US population and more than doubles every 30 years. “It’s not surprising people are putting on earphones or even noise cancelling headphones to try and create a quieter or more congenial environment,” he said. “As you raise background sound levels, it has the same effect on your hearing that fog would have on your vision. Instead of having this expansive experience of all the sounds around you, you are aware of only a small area around you,” he said. “Even in most of our cities, there are birds and things to appreciate in the environment, and there can be very rich natural choruses to pay attention to. And that is being lost.” People quickly become accustomed to changes in their environments, including rising noise levels, and, over time, Fristrup fears that we will accept far worse environmental conditions than we should and forget how much quieter the world