And tomorrow's Americans will be louder, still.

In 2011, researchers monitoring noise levels in remote regions of Oregon's Crater Lake National Park declared that ambient human noise was all but inescapable in the U.S. New data corroborates their claim. This map, based on 1.5-million hours of noise-monitoring across the country, illustrates the extent of the growing human clamor.

Image Credit: National Park Service Natural Sounds and Night Skies Division

The map depicts estimated median sound levels for the contiguous United States, and is color-coded according to loudness as measured in decibels. These estimates account for all sounds, by the way, not just human ones. That said, some of you (readers of xkcd, especially), will be quick to note that it bears a striking resemblance to a human population map. This is entirely unsurprising; it makes sense that humanmade noise pollution would correspond geographically with human distribution and population density.

But here's what is surprising: "Both noise and light pollution are growing far faster than the human population of the United States," Kurt Fristrup, senior scientist for the National Park Service's Natural Sounds and Night Skies Division, told reporters at the annual meeting of the American Association for the Advancement of Science on Monday. "They're somewhere between doubling and tripling every 20 to 30 years."

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This observation suggests we are the loudest Americans in history. If conditions hold, tomorrow's Americans will be louder, still.

Fristrup was one of three presenters on a panel devoted to human-made noise and light pollution. The symposium covered how we can predict and map these phenomena at a continental level, their human and ecological impact, and the potential role of citizen scientists in studying and managing their spread. Science's Emily Underwood summarizes Fristrup's presentation:

Based on 1.5 million hours of acoustical monitoring from places as remote as Dinosaur National Monument in Utah and as urban as New York City, scientists have created a map of noise levels across the country on an average summer day. After feeding acoustic data into a computer algorithm, the researchers modeled sound levels across the country including variables such as air and street traffic. Deep blue regions, such as Yellowstone National Park in Wyoming and the Great Sand Dunes National Park in Colorado, have background noise levels lower than 20 decibels—a silence likely as deep as before European colonization, researchers say. That's orders of magnitude quieter than most cities, where noise levels average 50 to 60 decibels.

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Remember, decibels are measured on a logarithmic scale. 70dB is twice as loud as 60dB, four times as loud as 50 dB, eight times louder than 40dB, and so on. 20 dB is roughly comparable to "the sound of rustling leaves," which is about what you'd hope to find in, say, a National Park. In fact, there are laws in place that aim to preserve this level of quiet.

According to Section 1.4 of the Organic Act of 1916, park officials are legally obligated to minimize "the impacts of influences originating outside park" (including noise), and to "restore to the natural condition wherever possible those park soundscapes that have become degraded by unnatural sounds." Fristrup says noise pollution has yet to rise to a level requiring legal action, but that it is already having an effect on the park experience.

Underwood reports that the NPS is using the map to identify places where humanmade noise is affecting wildlife, but Fristrup told reporters that he fears for future humans, as well. "This gift that we're born with — to be able to reach out and hear things that are hundreds of meters away, all these incredibly subtle sounds — it is in danger of being lost to generational amnesia," he said.

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Joining Fristrup on the panel was Cal Poly biologist Clinton Francis, who spoke to the ecological impacts of humanmade sound. In a study published Monday in the journal Global Climate Biology, Francis describes how low-frequency human noise is likely to drive out birds that sing at similar frequencies, and birds of prey who may find it more difficult to listen and hunt over an anthropogenic clamor. The results, writes Francis, suggest that humanmade noise "is a powerful sensory pollutant that can filter avian communities non-randomly by interfering with the birds' abilities to receive, respond to and dispatch acoustic clues and signals."

For more, see NBC News for some solid coverage of the presentation. For more on the National Parks Service's Natural Sounds and Night Skies Division, see here.