Last reviewed 31 August 2021

As climate change-related extreme weather events become more frequent, hotter and wetter, previously unthinkable unorthodox solutions are increasingly becoming thinkable, Jon Herbert explains.

When 19th century French science-fiction writer Jules Verne described fantastic concepts like boats travelling underwater, heavier than air flying machines, and even the ridiculous notion of humans travelling to the moon and returning safely, his ideas seemed exciting but farfetched.

Verne’s vivid imagination lives on. Modern engineers, scientists and futurologists are conjuring up equally bizarre-seeming ideas that with luck and persistence might, and probably must, work in practice as necessity becomes the mother of urgent environmental invention.

However, rather than adventure and exploration, today’s focus is on finding practical if extreme solutions to warming and climate change on a global scale.

Last chance cooling saloon

Why now? Climate change seems to be gaining momentum faster than expected, with wildfires in American and Siberia, floods in Europe, China, India and London, plus the UK’s first Met Office extreme heat warning.

As a result, more attention being given to radical ideas and drastic interventionist remedies.

They range from painting city roof tops reflective white to planting seaweed forest, spreading weathering rock dust, bubble curtains lifting deep cold ocean waters to the surface to kill hurricanes, artificially-whitened clouds, and high-altitude micro-mirrors reflecting the sun’s rays back into space.

The Oxford Geoengineering Programme is studying the issues in depth, as is the Centre for Climate Repair at Cambridge.

Who pressed the big button?

But geoengineering raises both complex technical and ethical issues.

Will mega-scale solutions work? Will their benefits be spread evenly? And importantly, who will press the button or flick the switch on projects which once started might be irreversible?

There are also doubts about unknown side-effects. Are experiences like the rabbits and cane toads released by humans in Australia which became pests and invasive species a warning?

Side-effects and moral hazard

With many innovative projects underway in the run up to November’s UN Climate Change Conference (COP26) there are also moral hazard questions — would global geoengineering solutions stop high carbon industries from cutting their emissions? And could new technologies be exploited by states or actors with malicious intent?

From mundane to magnificent

When it comes to technologies, geoengineering is often split into two broad categories.

To reduce the greenhouse effect carbon geoengineering looks at carbon dioxide removal — “negative emissions”. Solar geoengineering focuses on albedo modifications to reflect sunlight back into space.

Simple solutions are attractive but not always workable. Planting enough trees in the right place to offset human-made emissions may not be practical. Seeding seas with nutrients like iron to promote phytoplankton blooms which absorb CO2 is not stable.

Direct air capture (DAC) that aims to take carbon out of the atmosphere rather like trees, but faster and on less land, is in its promising infancy but will perhaps only ever be a local solution (see and

But rewilding coastlines on a huge scale might be an alternative before getting into complex technical solutions. One route is biological. Another is chemical mineral.

Sub-sea forests

Looking at biology first, three types of coastal ecosystems store carbon as sediments or soil - mangroves, salt marshes and seagrasses. Jointly, they remove more carbon than all land forests. Kelp also absorbs some 600m tonnes of CO2 a year globally.

Many mangrove swamps and salt marshes are being destroyed by coastal developments. Since 1980, the UK has lost an estimated 35% of its extensive seagrass meadows. Could restoring them could be relatively straightforward?

Project Seagrass is exploring ways to create new meadows. The Wallsea Island Wild Coast Initiative in Essex is building up salt marshes with clay, chalk and gravel from London’s Crossrail. Scale is the challenge!

Diving deeper

On the mineral route, Project Vesta wants to accelerate the natural rock weathering process to chemically remove a trillion tonnes of CO2. It calculates that spreading sand-sized particles of the common volcanic rock olivine along 2% of the world’s 1.16 million kilometre coastline could capture all 100% of the world’s annual carbon emissions.

Rocks like olivine dissolve slightly in rainwater in a chemical reaction that removes atmospheric carbon dioxide. Marine-calcifying organisms then use this to build corals and shells. Their remains fall to the seafloor as sediments that become limestone. Olivine weathers easily and could dissolve on a human-relevant timescale, project leaders say.

By unit of volume, ocean water can hold 150 times more CO2 than air; it already stores some 30% of the waste carbon dioxide emitted by humans. But the possible side-effects of complex chemistry, plus whether natural weathering would increase at an unnatural pace, are unknowns.

On the plus side, the researchers say costs could be low, with gains 20 times larger than emissions from olivine’s mining and transport. Weathering also locks carbon away irreversibly.

Upgrading soil

A land-based alternative “suited for rapid upscaling” could be “amending soil” with powdered basalt that not only absorbs carbon but by increasing soil fertility could “potentially enhance ecosystem carbon storage” (see

Adding electricity

Another approach is applying an electric charge to seawater to make it alkaline and create conditions where CO2 reacts with magnesium and calcium to form limestone and magnesite sediments.

By-product hydrogen could be used as fuel; the downside is building machines and networks on a scale needed to make a difference… and the time taken.

Holding back methane

One other geoengineering innovation could be to limit the warming side-effects of events like the mass release of methane from thawing permafrost by cooling the edges of the Arctic Ocean with cloud-brightening technology.

This might involve large fleets of specially-designed vessels with high ‘masts’ that spray a fine seawater mist into clouds so salt can make them brighter and more able to reflect the sun’s heat. Again, a better understanding, vision and funding are needed.

There are also concerns that weather patterns like monsoons depend on heat differences between continents and oceans. Cooling the North Atlantic to, say, save sea ice or Greenland glaciers could also affect precipitation in the tropics. Science doesn’t yet have the answers.

Damping down hurricanes

A new ocean project is also looking at the possibility of neutering hurricanes by cooling the surface seawaters from which they take their destructive energy.

OceanTherm , formed in 2017, adapts established technology to reduce storm intensity. It uses “bubble curtains” to release compressed air into deep cold waters and lift them into warmer surface water. The hope is to kill off hurricanes at source. But again, there are fears of changing the landfall of storms and increased flooding.

Turning down the sun

The National Academies of Sciences (NAS) thinks the US must establish a five-year $100m to $200m solar geoengineering research programme to find ways of ‘dimming’ the sun. It stresses that cutting emissions is the main priority, but “worryingly slow progress” means all options must be examined.

Three types of solar geoengineering are considered: launching trillions of tiny reflective particles into the stratosphere to block sunlight; using particles to make low-lying clouds over oceans more reflective; and thinning high-altitude cirrus clouds. Major volcanic eruptions do this naturally.

Opponents cite risks from rogue states and crop damage, adding that systems would have to be maintained continuously to avoid sudden temperature hikes.

Inexpensive solar geoengineering

Aerosol geoengineering is the most likely global solar geoengineering candidate but to date has been largely confined to computer modelling — with positive results.

Harvard University research suggests the $2 billion to $2.5 billion annual cost of launching millions of tonnes of sulphate particles into stratosphere as a protective sheath around the planet could be “remarkably inexpensive”. It would also be highly uncertain and ambitious, but technically possible.

Special aircraft would carry particles to the 12-mile (20km) altitude needed to keep them aloft for a year or more; rockets are far too expensive but high-altitude balloons might be an option.

The team has calculated costs for a 15-year programme with six to eight new planes added annually, plus the expense of crews, maintenance, insurance, fuel, landing charges, spares and training.

Some 4000 flights a year initially, rising to 60,000 with nearly 100 aircraft, could limit annual warming to 0.1°C with a total reduction of 1.5°C — the safe limit predicted by climate scientists.

However, again the potential costs of compensating for droughts, floods and food shortages could be much larger than the engineering costs. Geoengineering isn’t necessarily a zero-sum proposition.

Even so, Jules Verne would have been impressed.