Particles from fossil fuels 'affect the growth of corals'

Researchers have found the strongest evidence yet that aerosols from burning fossil fuels are affecting coral growth.

Soot and other particulates have slowed the growth of coral off Belize and Panama

They say that these sooty particles can cool sea surface temperatures and limit the size of reefs.

But they also believe this chilling effect could prevent the corals from bleaching in warmer waters.

The research is published in the journal Nature Geoscience.

Coral reefs all over the world have been under pressure from a range of human impacts.

With a rise in global ocean temperatures recorded over the past century, there have been growing concerns that the warmer waters will become more acidic and as a result will bleach the corals.

Dirty air

This does not kill them but makes them much more likely to die. This has been well documented in the Caribbean.

Now, a team of researchers has found that as well as the warming waters, fine particulates of different types are affecting reefs near Belize and Panama.

These aerosols are made up of soot from burning coal, elements from volcanic eruptions and sulphates from fossil fuels. They circulate in the atmosphere and are believed to block solar radiation and make clouds more reflective.

Developing countries such as Indonesia are home to a majority of the world's coral

In this latest study, the scientists looked at records from coral skeletons, ship observations and climate models to compare coral growth rates from 1880 to 2000. They found there was a correlation between increases in atmospheric aerosols and decreases in the growth rates of coral.

"Particulate pollution reflect incoming sunlight and make clouds brighter," said research team-member Dr Paul Halloran from the UK Met Office Hadley Centre.

"This can reduce the light available for coral photosynthesis, as well as the temperatures of surrounding waters. Together, these factors can slow down coral growth."

So strong was the effect on the reefs that the researchers believe it usurps other factors, said lead author Lester Kwiatkowski.

"For multi-decadal variability, over the historical period, the major cause was aerosols as opposed to climate change or ocean acidification," he explained.

The team was able to point to specific incidents, such as the drop in sea-surface temperatures between 1960 and 1970 caused as a result of rising levels of particulates from post WWII industrial expansion in the US.

The researchers were also able to see a rise in temperatures after 1970 - the consequence of clean air legislation cutting emissions of soot and sulphates.

Accidental engineering

But while the cooling effects of these particles may be keeping the corals from growing, according to this work, it might also be preventing bleaching.

"It is quite difficult to say what the corals would have done if these aerosols were not in the atmosphere. It could have been, to some extent, that these were providing protection from thermal bleaching," said Lester Kwiatkowski.

Looking ahead, the researchers say that understanding the impact of aerosols is critical to the survival of coral reefs.

As the majority of coral is in the waters around developing countries, they may be inadvertently performing a type of geo-engineering on the reefs.

"Many people are arguing that Australia should be putting aerosols into the atmosphere to protect their coral reefs," said Lester Kwiatowski.

"And in parts of the developing world through atmospheric pollution, they be inadvertently doing such things," he added.

From BBC News-Science/ Environment