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Has lockdown made the world a quieter place?

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With levels of road transport, air travel and industrial output lessening dramatically during the Covid-19 lockdown, one side-effect has been a reduction in noise pollution. However, there’s more to ‘global quieting’ than being able to hear more birds.

According to the World Health Organisation, noise affects over 100 million people in Europe alone. Exposure to chronic noise pollution not only causes obvious problems such as hearing loss and sleep deprivation, but is also linked to high blood pressure, heart disease and cognitive impairment in children. Road traffic noise is said to contribute to at least 12,000 premature deaths annually in Europe, amounting to a loss of 1.6 million high-quality-life days. The European Environment Agency (EEA) has found that the same number of children are experiencing either learning difficulties or disruptions due to excessive aircraft noise.

WHO says that road traffic is the worst cause of noise pollution, followed by trains, aeroplanes and heavy industry. If that’s not enough, noise can really get you where it hurts. Researchers at New York University (NYU) have found that house prices can decline by up to 2 per cent per decibel. They also found that residents of the Big Apple use the ‘311’ non-emergency phone line to complain about noise more than any other reason.

There could be some relief in the form of ‘global quieting’, a term coined by National Geographic to describe the phenomenon of a hushed planet as an unintended consequence of national lockdowns the world over. In both the UK and Europe there has been a reduction in air traffic of 90 per cent, car usage has dropped by more than half, and train services have been cut heavily.

Experts at the British Geological Survey have found that in April 2020, the level of human-generated – or anthropogenic – noise fell by as much as half, compared with levels recorded before the coronavirus restrictions came into force in the UK. Dr Brian Baptie, head of seismology at the Survey, says that the organisation has a network of around 100 sensors deployed nationwide in order to monitor earthquakes and volcanic activity. But his seismometers also track other activities in the Earth’s crust, ‘seismic noise’, created anthropogenically, such as road, rail and factory noise. In effect, as commuters make fewer journeys, the Earth’s surface vibrates less.

Baptie says that noise levels “have gone down by somewhere between 20 and 50 per cent” at nearly all of the organisation’s monitoring stations since lockdown. Meanwhile, scientists at Royal Holloway, University of London have reported a 30 per cent drop in seismic noise near King’s Cross station, while Dr David Cornwell, a geophysicist at the University of Aberdeen, has recorded a drop in campus noise levels of 65 per cent since the students were sent home mid-March.

The upside of the drop in human noise, for seismologists at least, is that they are now able to detect minor geophysical events that were hard to identify before lockdown. Today, says Cornwell, “if a minor earthquake happened in Japan, I would be able to record it in my office or in our instruments across the UK”.

The EEA says that this drop in environmental noise represents a short-term gain rather than a long-term benefit. According to its noise expert Eulalia Peris, “Noise pollution from transport sources is linked to economic activity. Therefore, in the current situation we expect to see a significant reduction in transportation noise levels in the short-term due to decreased mobility demand.” The strong implication is that as society emerges from lockdown and transport usage gradually returns to its previous levels, so too will noise pollution levels.

Despite the fact that noise is the second largest environmental cause of health problems (coming in a close second to air pollution), it is something we have learned to live with, says Peris. “We have grown accustomed to unhealthy noise levels in cities because that’s what we are hearing every day.” She goes on to make the point that while a reduction in noise pollution might well be one of the more pleasant outcomes of the Covid-19 containment measures, it has also provided us with an opportunity to hear for ourselves “the real impact noise has on our lives”.

‘We have grown accustomed to unhealthy noise levels in cities because that’s what we are hearing every day’

Eulalia Peris, European Environment Agency

When the guns fell quiet on the Western Front just over a century ago, one of the first things that the frontline soldiers of the First World War noticed was that, among the silence of the ceasefire, they could hear birdsong. It’s such an enduring image of peace that Sebastian Faulks used the word as the title of his Great War novel ‘Birdsong’. Likewise, one of the curious changes we started to notice in our lockdown world was, as one caller on a Talksport Radio chat show observed, the birds are getting louder. Not entirely true, replied ornithologist Bill Oddie, who explained that what was really going on was that due to the reduction in background noise birds only seemed to be louder. Although that’s far from the whole story.

Scientific data currently suggests that the reduction in anthropogenic noise could mean that birds are actually getting quieter, simply because they no longer have to compete sonically with the internal combustion engine to defend their territories and attract mates.

Dr Henrik Brumm of the Max Planck Institute for Ornithology in Germany compares the situation with humans having to raise their voice in crowds or other noisy environments. Brumm’s research has shown that birds respond within 300 milliseconds to a change in background noise and adjust accordingly: “When their surroundings become louder, they sing louder.” His research has also shown that birds sing more quietly during the early weekend mornings when there is less road traffic.

The fact that the lockdown coincides with the spring mating season also means that we could be in for a new generation of not only more, but healthier hatchlings. A recent study at the Max Planck Institute has shown that road noise has a negative effect on embryo development and mortality in zebra finches. While the net effect is that the increased bird population might produce more noise than the pre-lockdown population, Brumm is not prepared to speculate without real-time data. It “stands to reason”, he adds, that the current period of quiet could mean that individual birds might “be singing more softly than usual”.

Even as the effects of the coronavirus take their toll in terms of loss of life and disintegrating economies, global quieting is presenting scientific researchers with an opportunity to study the world under a bizarre set of conditions that academic institutions the world over are touting as a ‘unique’ event.

This prolonged reduction or absence of background noise, says Thomas Lecocq, a geologist at the Royal Observatory of Belgium, is allowing scientists to investigate more closely phenomena that were previously “lost in the hubbub of human life”. Since world leaders made the request for people to stay at home, the resulting “prolonged hush” in densely populated urban areas intrigued Lococq to the point where he started to post his data on social media alongside data from other scientists who had noticed similar patterns. The curious effect of this was summarised by California Institute of Technology PhD candidate Celeste Labedz, who wrote: “having a lower level of background noise is just like being in a quieter room. We can hear more sounds.”

These sounds will contribute to research that will help us to fine-tune our response to health crises in the future. One fibre-optic network seismic noise study based at Palo Alto, California, can generate data so precise that it is possible to identify individual vehicle movements. Studying traffic activity on such a fine scale could have an effect on the way we manage traffic around hospitals in future, says one of the project’s seismologists, Siyuan Yuan.

Currently, Lecocq is urging researchers around the globe to contribute to a study he is working on that aims to give scientists access to data related to global quieting.

At the moment we live in a world where the ambient noise level has fallen by as much as 10dB due to reduced road traffic alone. That may not sound like much, but as Rueben Peckham, director at Southampton-based 24 Acoustics, says: “A 10-decibel reduction in noise level is highly significant – roughly a perceived halving in subjective loudness.” And so it’s hardly a surprise that birdsong is playing a more prominent role in our lives.

As the EEA’s Eulalia Peris warns, this chance to jump onto global quieting and convert low noise into long-term societal benefits will only happen if we learn from life under lockdown conditions and apply that to “a long-term strategy on mobility and transportation systems”.

Wildlife

Birds are changing their tunes

Assessing the impact that human-​generated or anthropogenic noise has on the natural world is fast becoming a growth area in academia. While it has been known for decades that bird calls in cities will be different from those of rural birds of the same species, scientists in Canada are currently researching what effect the oil industry is having on the savannah sparrow. It turns out that in order to get their mating calls heard above the din of the drills, turbines, engines and pumps that are a feature of the Canadian landscape, these sparrows are having to modify their songs in complex ways that scientists are only starting to understand.

University of Manitoba biologist Miyako Warrington has led a study into how the sparrows cope with the noise. Analysis of waveforms captured by birds singing in their natural quiet environment has been compared with those from birds living close to generator-powered screw pumps. The results show that the sparrows have lowered the pitch of the opening notes of the call while modifying mid-section into a screech in order to overcome the noise of the pump. The team has analysed the song of 73 birds across a territorial radius of 125 miles (200km) around the city of Brooks, which is at the centre of Canada’s oil industry.

While it might be tempting to think that call modification has cured the savannah sparrow’s communication problem, Warrington warns that evolution rarely works in such straight lines. He says he’s worried that by, “changing pitch from, say, George Clooney to Bart Simpson”, the females might miss the male mating cues.

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