Global warming: The disappearance of clouds leads to lower temperatures

With the help of snow cannon-like machines, salt particles are lifted from the sea surface and thrown upwards as part of the marine cloud removal process. There the wind picks them up and transports them to the higher cloud layers.

Once in the cloud, the water eventually binds to the salt, resulting in a higher concentration of particles and much smaller cloud droplets. “They are more effective at scattering light and reflect more incoming solar radiation,” explains the atmospheric physicist. Anna Posner From Goethe University Frankfurt to science.ORF.at. The result is lower temperatures under the cloud.

The method is (theoretically) harmless

The salt stays in the cloud for a few days until it returns to the sea the next time it rains. This also makes the use of salt particles completely environmentally friendly, because “salt is naturally present in much larger quantities in the sea and in nearby coastal areas anyway,” says Posner.

However, there is little research into whether salt in clouds can cause damage if rain falls on land rather than over the sea. According to Posner, this is not a real cause for concern because the operation is primarily intended to be used over the sea and will not affect land masses. The effect is likely to be greater over the sea, because the shallow, dark ocean will absorb a lot of solar energy there.

Side effects have hardly been researched

The fact that marine cloud lightening basically works has already been proven in a few studies. Among other things, the procedure was carried out in Australia in the area the great Barrier Reef Tested. “These small-scale field studies have shown that the particles actually blend into the clouds and make them more reflective,” Posner says.

According to her, studies so far clearly show that this measure is particularly effective at the regional level. “This may lead to the possibility of relatively localized and small-scale action against excessive temperature increases without causing any unwanted side effects.”

The potential side effects of marine cloud brightness still ring alarm bells for the atmospheric physicist, she explained to Science.ORF.at. Especially when it comes to expanding the process for global use. “There are still a lot of uncertainties here that have not been examined in detail yet.”

It is possible to visualize heat waves and extreme events

It is unclear, for example, how much an artificial change in the cloud architecture will affect other areas that are not directly in the application domain. According to the expert, the opposite effect could occur there due to weather and wind characteristics, which are usually closely related. “Some previous studies have shown that the cooling is not evenly distributed. This means it will be cooler overall, but it may also get warmer in some areas.

The reason for this lies in physical phenomena: cooling causes changes in areas of atmospheric pressure. To compensate for the cold, warm air flows to other areas and causes temperatures there to rise. Posner cites the climate phenomenon as an example “La Niña”which is, so to speak, an analogue of the more famous one “El Nino” It is happening. Temperatures are also falling in most regions of the world – but in certain regions the La Nina phenomenon causes heat waves.

It is also unclear whether this measure might lead to an increase in extreme weather events in certain areas. “Of course, all of this still needs to be clarified in detail before it can be rolled out globally,” says the atmospheric physicist.

International cooperation

To this end, there will be a large-scale research project in the USA, where experts from all over the world will study the potential of marine cloud lightening, but also its many risks. The unofficial start of the long-term project was an international workshop in 2022. This was also the outcome evaluation The current state of knowledge and questions that still need clarification, which were recently published in the journal “Science Advances”.

Posner was also involved in the work. The most important key messages from this are clear to her: “It won't work without extensive field trials. We simply have too many uncertainties in current models to be able to rely on this data alone.” “We need a research approach that includes all areas that could be affected by the brightness of marine clouds from the beginning.” It was first considered from a physical and climate perspective – but Social, ethical and political aspects have not yet been taken into account.

Usage is still years away

Posner cannot currently estimate when marine cloud brightening will actually be used on a global scale. However, she hopes to conduct large-scale field experiments and reach new results in the next five years, because “otherwise the pressures from worsening global warming caused by human activity will be so great that at some point they will have to move.” Very quickly”. It is therefore necessary to know exactly what consequences and side effects large-scale marine cloud brightening will bring.