What’s the challenge?

Society needs to decide whether geoengineering, failing attempts to curb emissions, should be researched as plan b. Are the dangers associated with geoengineering too great? Should we purely be focusing on the challenge of mitigating carbon emissions?

What is geoengineering?
Geoengineering refers to the deliberate manipulation of the earth’s climate.

Is geoengineering detracting from the real issue?
There is a risk that serious consideration of geoengineering could give the impression that the need to reduce carbon emissions is not as important and that global warming has a possible technical solution. If serious consideration is given to researching geo-engineering projects, the pressure might be taken off governments to tackle the source of climate change and continue the decarbonisation of society.

Suggested geoengineering techniques:

  • Put giant orbital mirrors into the atmosphere to bounce sunlight back into space
  • Ocean fertilisation: Put iron into the oceans. The nutrients encourage the growth of huge blooms of algae or phytoplankton. The phytoplankton and algae absorb CO2 as it grows, and should sink to the ocean floor when they die, taking the captured CO2 with them. However there are concerns around the long-term impact on ecosystems.

  • Increase reflectivity: Paint roofs of buildings white to increase their solar reflection
  • Artificial trees: design tree-like machines that ‘scrub’ the air clean of pollution using absorbent membranes. However it is unclear whether the technology would be efficient at large scales or how and where the captured CO2 would be securely stored.
  • Cloud reflectivity: Use a specially designed ship to spray salt water droplets into the air. Water droplets condense around salt particles and form clouds. Clouds increase the albedo effect.
  • Sulphur screen: Add a screen of sulphur particles at high altitudes in the stratosphere. These particles help to partially reflect the Sun’s radiation back into space. The sulphur shield would aim to recreate the natural process that occurs during volcanic eruptions. However there are concerns about sulphur resulting in respiratory diseases and acid rain.


Extensive tests need to be carried out to determine the global consequences of geoengineering projects, however this is virtually impossible. Controlled geoengineering experiments are unable to be carried out and reversing projects that went wrong would be extremely difficult and costly.

One solution identified would be to monitor how the atmosphere responds to volcanic eruptions, a natural process that is similar to some proposed geoengineering solutions. Volcanic eruptions are known to project large amounts of sulphur dioxide into the atmosphere, which have been recognised as having a cooling effect on the globe.

The challenge will be to balance one form of environmental risk against another; deciding whether the consequences of geoengineering projects outweigh the threat that continued global warming poses.

Case study of geoengineering

: In 1995, a team of American oceanographers added half a tonne of iron to waters around the Galapagos Idlands. As a result the ocean turned green and plankton bloomed.

By the end of the experiment, the scientists had calculated  the small area of newly fertilised plankton has absorbed an additional 7,000 tonnes of CO2. This is equal to 2,000 fully grown trees.

Volcanic eruptions and the climate

  • 10 million tonnes:  The amount of sulphur that was ejected into the atmosphere in 1991 from the eruption of Mount Pinatubo in the Philippines
  • 0.6°C: The drop in recorded temperature across the Earth for two years after Pinatubo eruption

Panel discussion

Dr Paul Johnston is principal scientist at the Greenpeace Research Laboratories and Head of the Science Unit for Greenpeace International. Paul set up the Greenpeace Research Laboratories at London’s Queen Mary College in 1987. He has continued as the principal scientist since the group relocated to the University of Exeter in 1992.

He obtained a PhD on selenium toxicity in aquatic invertebrates, from the University of London, in 1984. Paul now has almost 20 years experience in providing scientific advice and expertise to Greenpeace International and national/regional offices around the world.

“We could argue that most of the attempts to engineer ecosystems to our benefit have been really quite damaging to planetary systems” Dr Paul Johnston



Professor David Keith University of Calgary, Canada
Environmental scientist Prof David Keith works at the intersection of climate science, way-new energy, and public power. His research has taken him into some far-out realms of geoengineering — dramatic, cheap, sometimes shocking solutions to a warming atmosphere, such as blowing a Mt. Pinatubo-size cloud of sulfur into the sky to bring the global temperature down.

His other areas of study include the capture and storage of CO2 , the economics and climatic impacts of large-scale wind power , and the use of hydrogen as a transportation fuel. Another interest: How we make decisions when we don’t have reliable scholarly data. He teaches at the University of Calgary, and was named Environmental Scientist of the Year by Canadian Geographic in 2006.

David has served on numerous high-profile advisory panels such as the UK Royal Society’s geoengineering study, the IPCC, and Canadian ‘blue ribbon’ panels and boards. David has addressed technical audiences with articles in Science and Nature, he has consulted for national governments, global industry leaders and international environmental groups, and has reached the public through venues such as the BBC, NPR, CNN and the editorial page of the New York Times.

“While we can adapt, natural systems don’t”, Professor David Keith



Further reading

There are many different views about geoengineering. Sciencewise conducted a public survey. Read the report at Experiment Earth? NERC Sciencewise public dialogue, 2010

New geoengineering studies sceptical of success, Geographical magazine, November 2014

Can science fix the climate? by Mike Hulme, Geographical magazine June 2014

A case for climate engineering by David Keith, Geographical magazine March 2014

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