Microbes that form clouds threatened by climate change

Species of airborne microorganisms are likely to decline even in the least damaging paths of climate change, research has suggested.

While the potential impacts of climate change on animals are well-studied, less is known about the way that microscopic lifeforms will react, even though they are responsible for nutrient cycling, diseases and even the weather.

Modelling by Spanish researchers suggests that almost a fifth of all bacteria in the air are likely to be lost in the worst-case scenario, where greenhouse gas emissions continue to rise throughout the twenty-first century. Other organisms, like fungi, are also expected to take a hit.

The scientists have called for more research into this area in order to be understand just how the hidden life of the air will be affected by climate change.

Dr Matt Clark, a Research Leader at the Museum who was not involved with the study, says 'Declines in these microbes could affect so much. 

'It would affect the carbon and nitrogen cycles which could slow down, or in some cases speed up, the process of recycling nutrients. There could also be impacts on agriculture. 

'However, at this level, the impacts are still very uncertain.'

The findings of this study were published in Scientific Reports.

The oncoming storm

Just as the sea is full of microscopic plankton, so is the air. While some small insects, like aphids, can occasionally find themselves blown into the atmosphere, many organisms call the skies home for large parts of their lives.

Known as aeroplankton, this diverse group consists of thousands of different living organisms. This can range from spores and pollen from fungi and plants, as well as countless viruses and bacteria. 

'From the days of Pasteur we've known that there are microbes in the air,' Matt says. 'That's how food spoils and bodies decay but also how diseases spread and essential symbiotes get around. 

'They perform vital roles like breaking down the soil to release nutrients and fixing nitrogen.'

After getting beyond the lowest layer of the atmosphere, these organisms can travel huge distances. Their small size allows them to stay in the air continuously as they move, allowing microbes to globe trot between continents.

Though they are small, their impact is mighty. Their size makes them ideal for ice to form around, which can lead to the creation of clouds and storms. In turn, this can cause more microbes to enter the atmosphere, continuing their spread around the world.

Eventually, these organisms will make land, with tens of millions of viruses and bacteria deposited on every square metre of the planet each day. The organisms can have a range of effects, from being diseases of humans and plants as well as helping extract nutrients from the air for ecosystems.

Despite the number of microbes and their impact on the planet, scientists don't know too much about them in comparison to their relatives in the ocean and elsewhere. 

'We know that the microbes move around, but looking at it in this type of detail is still a new area,' Matt explains. 'It takes quite a while to filter through a large amount of air to get even a small amount of biological material. Then we need to build up databases of what we find, and analyse them, in order to start to understand the differences.'

Climate change is set to have a significant impact on marine plankton, with less ice in the Arctic leading to large phytoplankton blooms as the microbes take it more sunlight. However, ocean acidification could see many species wiped out.

To assess what climate change means for their airborne relatives, researchers took water and snow samples every fortnight for six years from high in the Pyrenees mountain range. Microbes trapped in the precipitation were identified, and local climate data recorded.

Different scenarios were then modelled, with climate data changed over time to predict how each group of microbes would react.

Cloudbusting

The researchers found that the species richness of bacteria in the models was most affected by the amount of dissolved carbon in the rain and snow, with the most diverse groups doing better with more carbon. Meanwhile, the richness of eukarya, the domain of life taking in everything from fungi to plants and animals, depended on the different chemicals in the air.

Turning to temperature, they found that in the worst scenario, where global temperatures increase by up to 5 degrees by 2021, 15% of bacteria species would be lost by 2021. Eukarya species were largely stable until 2060, at which point they also began to decline.

The researchers then looked at the groups of bacteria and eukarya which cause diseases in humans and plants (pathogens). Plant pathogens were predicted to see a 15% fall in species in the worst case scenario, and a 5% fall in the intermediate pathway which is the more likely to mirror reality.

As for human pathogens, a slight fall in species was seen under the worst case scenario, and only minor differences in the others.

While a fall in pathogens might seem like a cause for celebration, the wider impact on airborne microbes could have severe consequences. Microorganism species which extract nitrates from the air and are vital for plant growth could be among those to be driven to extinction, posing a threat to crops worldwide.

Meanwhile, clouds may form less if many of the microbes around which they form are no longer present, reducing levels of rainfall.

While the exact consequences are currently uncertain, they have the potential for severe harm. The researchers have called for urgent study of how the little-known ecosystems of the air could change as a result, in order to mitigate any risks that a warming world may present to it.