Scientists are working on opportunities for artificial cooling of the Earth. So far, there are three technologies. Can solar geoengineering solve the problem of global warming?
“Humans are no doubt able to cool the planet artificially,” said Professor David Keith of Harvard University. He deals with solar geoengineering – a very controversial scientific field. It focuses on how humans could manipulate the sun’s radiation to the Earth to deter climate change. Here are the main technologies that could possibly allow this to happen, presented by DW:
On June 15, 1991, tons of ash and gas were released into the atmosphere during the eruption of Pinatubo volcano in the Philippines. It was the second largest volcanic eruption in a century. To the surprise of many scientists, the event cooled the Earth in the coming months by about half a degree. The tiny particles in the air, the so-called aerosols, reflected more sunlight back into space. The result: reduced warming of the Earth.
Scientists like Keith want to achieve the same effect artificially based on a theory called “Stratospheric aerosol injection.” The idea is to scatter aerosols in the stratosphere – between 15 and 50 km above the earth’s crust. There they will contact water particles and for a period of one to three years will reflect more sunlight than usual. In this way, “many of the major climate threats can be curtailed – such as changes in access to water, changes in temperatures, including extreme temperatures,” Keith said.
However, for the cooling effect to be lasting, aerosols must be dispersed over decades and on a large scale. Balloons, artillery, planes or huge towers could be used for this purpose. And the solution is not without risks – some scientists fear increased cataclysms over time, acid rain or damage to the ozone layer.
So far, the theory has hardly been put into practice – it was planned for the first time this year to experiment with a balloon in the atmosphere over Sweden, and then to assess the results and risks of the method. But due to protests from local people and environmental activists, the experiment was canceled at the last minute.
The sea like a mirror
It sounds incredible, but some scientists are exploring how the Earth can be cooled by covering large parts of its water cover with artificial foam. The procedure is called Ocean foaming or Microbubbles.
About 70% of the Earth’s surface is covered with water. The water, which is dark because of the depth, reflects very little sunlight and retains a lot of heat. According to the so-called Albedo effect, the brighter a surface, the less it heats up. This could also be used for water.
The idea is this: “Develop a foam that reflects some of the sun’s rays and then directs them to strategic points where a certain climate effect could be achieved,” said Corey Gabriel, a climatologist at the University of California, San Diego.
Theoretically, this foam could reflect ten times more sunlight than dark water surfaces. With enough foam, the planet could cool by 0.5 degrees Celsius. Some scientists suggest that the foam be applied by special ships or container vessels. This method has not been sufficiently studied so far and will not be implemented soon. And the consequences for marine ecosystems of applying huge amounts of foam to water are still completely unclear. In addition, the effects on climate and local weather would be difficult to control.
Cities in white
In the summer in many cities it gets really hot compared to less populated areas. In New York, for example, the temperature is between 1 and 3 degrees Celsius higher than in the surrounding area. The reason: dark roofs, streets and sidewalks heat up more than trees, lighter fields and areas where plants cast shade.
And for this there is a solution – the houses and roofs to be painted white. It is both easy and relatively cheap, and it will also cool down. A white roof is about 30% cooler than a black one. In traditional architecture in African, Arab and southern European countries, this has long been done to repel the heat.
“Local temperatures could drop by about a degree. On very hot days, when the sun’s radiation is very strong, the effect could be even higher,” said Professor Sonia Seneviratne, a climatologist at the Technical University of Zurich.
In New York, under a special program since 2009, more than one million square meters of roofs have been painted white. This color not only cools buildings, but also saves energy, for example for air conditioners.
Scientists predict that if all roofs and sidewalks around the world are painted white, greenhouse gas emissions will be saved as much as 700 medium-sized coal-fired power plants.
Will solar geoengineering come into operation?
Repainting the roofs in white has an effect on the local climate, in addition, there are no dangerous side effects. However, due to the potential risks, the spraying of aerosols in the stratosphere and the application of foam on the water surface will hardly be applied soon.
There are two camps in the scientific community that are in opposing positions on whether it is worth investing in research in the field of solar geoengineering.
“If we don’t do research, the next generation will have to make decisions without the knowledge they need – and it could go so far as to apply methods of this kind without research,” said David Kate. “That would be stupid, and I think there’s something like an ethical imperative – to provide information to the next generation.”
Even if many scientists think differently from Kate, they are all united in one respect – we need to reduce greenhouse gas emissions as quickly as possible and in the long run find ways to adapt to climate change. Because even solar geoengineering will not be able to turn the clock back and prevent global warming.
