Geoengineering could fight climate change

International political efforts to curb greenhouse gas emissions are not going well: what are we to do to mitigate their warming effect? Some scientists and engineers propose a different approach, which involves dealing with gases and their effect in the atmosphere. It is called geoengineering – the large-scale intervention in the Earth’s natural systems to counteract climate change.

Geoengineering focuses on ways to remove carbon dioxide from the atmosphere, or on offsetting warming effects by targeting the overall amount of solar energy hitting the Earth. Let’s have a look at some ideas.

Removing CO2EMOVING CO2

1 – Photoplankton and iron

The ocean is full of living things that use photosynthesis to capture CO2, particularly single-celled algae called phytoplankton. When they die, they sink deep into the ocean, taking all that CO2 with them. Phytoplankton also need iron to grow. Some scientists have proposed increasing the ocean’s iron content, causing the phytoplankton population to increase, thereby removing more CO2.

Experiments suggest this idea, known as ocean fertilisation, can work but there are concerns that pumping iron into the sea will have unintended effects on marine ecosystems. At present large-scale ocean-fertilisation projects are banned by international treaty.

2 – Carbon filtering

There are many proposals that involve removing CO2 from the atmosphere and burying it in the ground – a process called carbon sequestration – but one company in Switzerland has another idea: grab it and use it for whatever you want!

The company, called Climeworks, has developed a technology, called Direct Air Capture, that uses huge fans to suck air through a filter to which CO2 chemically bonds. When heated, the filter releases the CO2, which can then be sold for other uses, such as growing vegetables in greenhouses, making carbonated drinks or even fuel.

Such uses don’t remove CO2 from the air permanently but the technology does stop more gas being produced for commercial purposes. More permanent fixes are also available. At its CarbFix plant in Iceland, Climeworks has found a way to turn the CO2 into stone, sequestering it for millions of years.

3 – Afforestation

Perhaps the least spectacular but most sensible geoengineering proposal is to simply plant trees. Lots of them. Trees use energy from sunlight to draw in carbon dioxide and water. They breathe out oxygen and use the carbon to build their trunks and roots.

It’s a good idea, for all sorts of environmental reasons, to not only stop cutting down the world’s forests but to replace the billions of trees already cut down. The feasibility of planting enough trees to offset the CO2 we are emitting by burning fossil fuels is, however, hotly disputed.

Calculations are complicated, but even the most optimistic estimates figure we would need at least a billion hectares of extra forest. That’s an area the size of Canada. According to scientists from the Potsdam Institute for Climate Impact Research, tree planting can only play a limited role – though an important one “if managed well”.

Solar radiation management

4 – Stratospheric aerosol injection

In 1815 a volcano in Indonesia called Mount Tambora produced the largest eruption in recorded history. It ejected huge amounts of aerosols – extremely fine particles suspended in the air – into the upper atmosphere, reflecting away so much sunlight that the following year was known as ‘The Year Without a Summer’.

Now some scientists want to use this same principle to offset greenhouse gas effects. Harvard University is preparing to launch the first ever aerosol injection experiment outside a laboratory, known as the Stratospheric Controlled Perturbation Experiment (SCoPEx). A balloon will be launched high into the atmosphere. There it will release an aerosol, and scientists will observe the effect. Eventually they hope to understand the process well enough to safely use the technique on a large scale.

5 – Albedo

Another idea is to increase the Earth’s ‘albedo’ – which is Latin for ‘whiteness’ and the measure of the amount of solar radiation the planet reflects rather than absorbs. Because whiter surfaces reflect more light than darker ones, a whiter Earth will reflect more of the Sun’s energy back into space, helping to keep temperatures cooler.

One way to do this is to make clouds brighter and whiter, an idea proposed by cloud physicist John Latham in 1990. The Marine Cloud Brightening Project at the University of Washington, Seattle, is trying to do this by spraying sea water into clouds over the ocean. The salt water will cause them to grow bigger and brighter.

Other proposals to increase the Earth’s albedo include painting houses white, planting crops that are pale and perhaps even laying out reflective sheets in deserts.

6 – Space reflectors

Particles in the stratosphere, bright clouds and painted surfaces are great, but what about doing something in space to reflect sunlight away? Could we build giant mirrors or umbrellas in orbit to keep the planet cooler?

All these ideas have been proposed, but would be so expensive that no one really thinks we could afford them.

Take the space mirrors, for example. This idea was proposed in the early 2000s by an astrophysicist named Lowell Wood, from the Lawrence Livermore National Laboratory in California. But even he thought it might be tough to do.

To be effective, 1% of the Sun’s light would have to be reflected. To achieve this, the mirrors would need to have an area of 1.6 million km2! That’s about the size of Iran.

This article appeared in Cosmos 79 – Winter 2018 under the headline “The world is in trouble. Call an engineer!”