Can asteroids and geoengineering the stratosphere save the planet?

28 July 2022 | Story Wendyl Martin. Photo Getty Images. Read time 8 min.
Amid the exponential effects of climate change, geoengineering and eco-regeneration are mooted as methods to cool our planet.

Shooting aerosols into the stratosphere to reduce solar radiation and to cool the earth’s surface; mining a mineral-rich asteroid belt in space to sustain our technologies; living on the moon … This is what the future could look like amid the effects of climate change and depleting resources. However, there are possible risks that can come from manipulating the stratosphere to deflect radiation, and tree-planting without planning.

As part of a series of virtual engagements, University of Cape Town (UCT) Vice-Chancellor Professor Mamokgethi Phakeng unpacked eco-regeneration and geoengineering with experts as possible solutions to save our planet from global warming and ecosystem disruption. The talk is part of a weekly series themed “Use the science of the future to shape your present” and is being held at the invitation of the Switzerland-based ‘think and do tank’ Geneva Science Diplomacy Accelerator (GESDA).

Stratospheric aerosol geoengineering

The director of the Climate Risk Lab at UCT’s African Climate and Development Initiative (ACDI), Dr Christopher Trisos, explained that eco-regeneration is about restoring damaged and degraded ecosystems while geoengineering suggests that we could offset global warming with technologies that deal with the symptoms.

“An example is stratospheric aerosol injection, whereby we would spray tiny particles into the stratosphere to form a thin veil to reflect some sunlight back to space, thus [offsetting] some global warming,” said Dr Trisos.


“Such technologies could reduce extreme heat and heatwaves but it could also change the geography of where malaria is transmitted on the planet.”

Dr Romaric Odoulami, Carnegie research fellow at the ACDI, said the ideas for solar geoengineering came from nature and observations of the effects of active volcanoes.

“When we have a major volcanic eruption, huge amounts of sulphur dioxide are ejected. This can reach as high as the stratosphere and constitute a thin barrier of aerosols that can act as a barrier to reduce solar radiation that can come to Earth’s surface and cooling it. This has been observed with a few volcanic eruptions. Scientists thought we could replicate that,” said Dr Odoulami.

Risky business

Both Trisos and Odoulami agree that the risks are too high to commit to this without considering the effects. Trisos maintained that reducing carbon emissions should be prioritised and that cooling from this technology could increase the threat of malaria.

“Such technologies could reduce extreme heat and heatwaves but it could also change the geography of where malaria is transmitted on the planet, making places more suitable for malaria and changing the risk of malaria for about a billion people across South America, Africa and Asia. With geoengineering, there is a high risk that some areas could win, and some areas could lose. It is too risky to bet the planet on geoengineering,” said Trisos.

He added: “If we switched on geoengineering, and then had to switch it off because of a failure, all the warming would come back quickly. This rapid shock from a failure could cause thousands of species to go extinct because we would have rapid climate changes within a decade.”

Scientists continue to study geoengineering on computer simulations. At UCT, said Odoulami, there is a research team that is working hard at analysing different aspects of solar geoengineering and how it could affect our climate and agricultural production in Southern Africa.

The cons of tree planting

Eco-regeneration often utilises tree-planting to offset carbon emissions. However, Trisos pointed out, in the wrong place, tree-planting can have negative effects on people and ecosystems.


“Tree-planting is not a silver bullet solution.”

“In the context of climate change, a lot of people talk about planting trees. In an African context, this is something we have to be careful about. Tree-planting is not a silver bullet solution.

“Many of the places that large tree-planting campaigns find suitable for planting trees are ancient and culturally important ecosystems such as savannahs and grasslands. We are losing biodiversity, grazing land, eco-tourism and water supply by planting trees in grasslands. We need to do the right restoration in the right places,” said Trisos.

The new space race

Dr Adriana Marais, a theoretical physicist with a PhD in quantum biology and the director of the Foundation for Space Development Africa, feels that some of our solutions lie somewhere between Mars and Jupiter, on the moon and in the earth’s orbit.

“The asteroid belt is between Mars and Jupiter – this is an interesting resource of metals, minerals and water … The motivation to look to the asteroid belt as a source of metals and minerals is because we cannot continue to harvest resources on Earth the way we do. Mining is one of the ways we contribute to the disruption of ecosystems,” said Dr Marais.

She pointed out that space resources are responsible for giving us power and water.


“Much of the water on our planet was delivered from space via asteroids and comets. Power and water are fundamentally space resources.”

“[The sun] is pretty much the primary space resource and source of all energy for life on Earth. The second most important resource is water. Much of the water on our planet was delivered from space via asteroids and comets. Power and water are fundamentally space resources.”

The impact of asteroids has brought us access to minerals from below the surface, and we don’t have to look far to see that. Marais explained the largest impact crater on Earth, the Vredefort Dome, hit our planet near Johannesburg around two billion years ago. Since then, we discovered the largest gold deposit on Earth in the Witwatersrand region, thus showing a correlation between places that have been hit by asteroids, and metal and mineral deposits closer to the earth’s surface.

“As Africans, can we sit together and say that eco-regeneration is more important than digging 4 km-deep holes in places where people and other species live. The amount of gold coming out of these mines is nowhere near what it was about 100 years ago. Can we contribute to a future where we don’t give up the surface of our beautiful planet and oceans that is teaming with life? Can we rather think about extracting our resources from the asteroid belt?”

Upcycle space waste

Marais also pointed out that we need to clean up our satellite debris mess, but this can be done in a way that recycles and creates new resources.


“Our priority for using technology should be out of respect for life.”

“In earth orbit, we have thousands of satellites. We use this technology every day as satellites bounce signals off each other and create the global payment network and navigation tools like GPS. The risk of catastrophic collisions with space stations or satellites is increasing.

“The number of satellites in orbit creates this debris problem which defunct satellites and remnants of space missions in orbit. The larger the structures, the bigger debris problem we are going to get. Entrepreneurially and as a form of recycling, we can build space stations with these materials in space.”

Marais felt that we can use space resources to assist the only life we know.

“Earth is the only planet we know of that hosts life. Our priority for using technology should be out of respect for life.”

The next Sunday session is scheduled for 31 July, with a discussion on science and diplomacy. Phakeng encourages all youth to watch the upcoming webinars to help them think about how they can use any of the future technologies spoken about in the series to help them shape the present.

Young people joining the sessions stand a chance to win an all-expenses paid trip to attend the 2022 Geneva Science and Diplomacy Anticipation Summit from 12 to 14 October. Submission requirements, deadlines and other details will be announced on 1 August 2022, after the fourth and final session.

Read more about the competition.

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