Light pollution is affecting the skies over more than half of our planet's key wildlife areas and is likely to increase, warns a new study.

Less than a third of Key Biodiversity Areas (KBAs) were found to have completely pristine night skies not polluted to the zenith, the point in the sky directly overhead.

According to the research conducted on behalf of conservation group Birdlife International, more than half of KBAs lie entirely under artificially bright skies.

Light pollution artificially brightens the sky and has been linked to a variety of negative impacts in ecosystems affecting microbes, plants and many animals.

Night-time light pollution has been shown to have wide-ranging effects on both individual species and entire ecosystems because it plays with their natural cycles.

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Light pollution is affecting the skies over more than half of our planet's key wildlife areas and is likely to increase, warns a new study. The map shows (a) pristine night‐time skies (ratio of artificial brightness to natural brightness ≤0.01) and (b) night‐time skies not polluted to the zenith (ratio of artificial brightness to natural brightness

Experts from the University of Exeter carried out a global assessment of the overlap between KBAs, places identified as being important for preserving global biodiversity, and the most recent atlas of artificial skyglow.

The team concentrated on 'skyglow' - light scattered and reflected into the atmosphere that can extend to great distances.

The extent of light pollution of KBAs varies by region, affecting the greatest proportion of KBAs in Europe and the Middle East.

Statistical modelling revealed associations between light pollution within KBAs and associated levels of both gross domestic product and human population density.

This suggests that these patterns will worsen with continued economic development and growth in the human population.

Dr Jo Garrett, who led the study, said that the results are troubling because 'many species can respond even to small changes in night-time light'.

'Night-time lighting is known to affect microbes, plants and many groups of animals such crustaceans, insects, fish, amphibians, reptiles, birds and mammals

Dr Garrett said that that there are an 'enormous range' of negative effects to these species.

(A) shows the proportion of Key Biodiversity Areas (KBAs) which have 0 and 100% coverage of pristine night‐time skies and skies not polluted to the zenith. (B) shows the total proportion of the area with pristine night‐time skies and skies not polluted to the zenith

'Trees produce leaves earlier in the season and birds to sing earlier in the day,' she said.

'It's also changing the proportion of predators in animal communities, and changing the cycling of carbon in ecosystems. Some effects can occur at very low light levels.'

'Pristine' skies were defined as those with artificial light no more than one per cent above the natural level.

The researchers explained that at eight per cent or more above natural conditions, light pollution extends from the horizon to the zenith - straight upwards - and the entire sky can be considered polluted.

The findings showed that just 29.5 per cent of KBAs had completely pristine night-time skies while 51.5 per cent contained no area at all with pristine night skies.

More than a fifth were entirely under night skies polluted to the zenith, but 51.9 per cent of KBAs were completely free of skies polluted to the zenith.

Just under half of KBAs in the Middle East (46 per cent) were entirely under skies polluted to the zenith.

The next-highest figures were Europe (34 per cent) and the Caribbean .

According to the research more than half lie entirely under artificially bright skies. Light pollution artificially brightens the sky and has been linked to a variety of negative impacts in ecosystems affecting microbes, plants and many animals (stock)

Study senior author Professor Kevin Gaston said: 'Unsurprisingly, the likelihood of skyglow tends to increase in areas with higher GDP, and in areas with higher human population density.

'This suggests that the proportion of KBAs experiencing skyglow will increase in parallel with the development of economies.'

He added: 'Skyglow could be reduced by limiting outdoor lighting to levels and places where it is needed, which would also result in considerable cost savings and lower energy use.'

The study is published in the journal Animal Conservation.