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Climate engineering Manipulating climate to fight global warming

Technology exists to change the climate: should this option be taken up or to be discarded?


The amount of CO2 in the atmosphere continues to increase and a world agreement on climate seems far off. So why not use technology to change the climate artificially? asks some Swiss scientists about the pros and cons.

An enormous mirror in outer space to deflect the sun’s light and cool the earth, or a ship that cruises the oceans feeding the algae and reducing the CO2 in the atmosphere – just science fiction?

“Not at all”, says Nicolas Gruber, a professor of environmental physics at the Federal Institute of Technology (ETH) Zurich. “The idea of mirrors in space is doable, though it would cost a lot. Fertilising the oceans is an approach that has already been tried. It has turned out to be rather ineffective, though”, he told

Taboo option

These two approaches are examples of climate engineering (also known as geo-engineering), the deliberate modification of the earth’s climate system on a large scale. Unlike techniques for making rain or artificial hail, the effects are planetary and long-term.

“As yet, climate engineering has not been discussed in international negociations on climate. It remains a political taboo – but that might change”, says Matthias Honegger of Perspectives, a Zurich consulting firm specialising in climate issues.

At the end of August he was in Berlin attending the first international conference on the topic, and he foresees that “if governments were to conclude that it is too late to get global warming down to 2°C and that their efforts to adapt at a national level are insufficient, then it is likely that they will be prepared to consider the possibility of climate engineering.”

CO2 Getting something back from carbon dioxide


Carbon dioxide is often considered the big bad wolf of greenhouse gases, a major cause of climate change and global warming according to specialists. But what if it could be used to produce energy and mitigate some of its impact?

Two Swiss projects are considering just that. One, private, is looking at how to suck up CO2 with its own version of a giant vacuum cleaner, while the other, public, wants to use it to produce methane thanks to small minerals known as zeolites.

At Zurich-based Climeworks, the aim has been for the past five years to develop a technology to continuously extract atmospheric CO2 that can then be used to produce synthetic fuels or applied for other purposes.

Carbon dioxide is collected by passing air through a specially-treated cellulose filter placed inside an extractor unit. Once it has reached its maximum capacity, the filter is heated using waste energy or renewable power to release extremely pure CO2.     

“We aim to de-carbonise some parts of the transportation sector such as aviation, which accounts for single-digit global CO2 emissions,” said Christoph Gebald, one of the company’s founders.

Aviation is responsible for around 3.5% of anthropogenic (man-made) climate change and has a 13% share of all the transport sector, according to the United Nations’ Intergovernmental Panel on Climate Change.

So far, Climeworks has been testing a so-called direct-air capture unit that can collect one ton per year of CO2, filtering around two million cubic metres of air, to demonstrate the validity of its approach.


Synthetic fuels

The result has been sufficiently interesting to attract the attention of German carmaker Audi, which sees the technology as one potential element of its strategy to develop vehicles running on synthetic fuels.

“What they need is a sustainable carbon dioxide source,” pointed out Gebald. “It can be either biogenic or atmospheric.”

However the first source, which results from combustion or decomposition of biologically-based material, is insufficient to meet the requirements of a single carmaker according to the young entrepreneur.

A test plant is now on the cards to see how the technology can be scaled up to provide enough CO2 for Audi’s production of synthetic fuels at its e-gas facility in Germany.

The technology is also on the fast-track to wider exposure. The company is one of 11 finalists in the Virgin Earth Challenge, a competition with a $25 million prize for the development of “an environmentally sustainable and economically viable way to remove greenhouse gases from the atmosphere.”


Extracting and purifying CO2 is just one step of the process towards producing synthetic fuels.

In theory, producing methane that could be injected into the natural gas network by combining carbon dioxide and hydrogen with a boost from an outside source of - ideally renewable - energy to kickstart the reaction is relatively straightforward, with water as a by-product. The process is known as the Sabatier reaction and was discovered early in the 20th century.

Doing this economically and quickly is a challenge though, as is separating the water molecules from the methane. Adding a catalyst, an element that speeds up the process, can help overcome some of the hurdles, but also carries the risk of producing toxic carbon monoxide (CO) and often low yields.


At the Federal Laboratories for Materials Science and Technology (Empa) near Zurich, researchers have been looking for a process that works at low temperatures and turned to zeolites, which are microporous minerals.

“Nickel-coated zeolites absorb the water generated by the process, almost no CO is produced and the gas at the end is methane,” said Andreas Borgschulte, the lead scientist on the project.

The result is far from perfect though. “It’s still experimental and the amount of water a zeolite can absorb is limited, so it has to be ‘dried out’, regenerated,” explained the researcher.

No silver bullets

Little more than a chemical reaction in a laboratory reactor at this stage, turning it into an viable process will require more work. While zeolites are easy for scientists to produce in small quantities, it would be necessary to find a cheaper way of producing them on an industrial scale.

There are also engineering challenges according to Borgschulte, such as upsizing the reactor, managing large volumes of gas, power and capital requirements. And to be carbon neutral, the process would ideally rely on CO2 from biomass, not from fossil fuels.

“Gas prices are very low, so it would be hard to compete,” Borgschulte said. “Synthetic gas would be more expensive by a factor of five.”

Pricing is also the challenge for Climeworks. Scrubbing CO2 from the air can cost up to CHF600 per ton according to one study from Zurich’s Federal Institute of Technology.

The company hopes to reduce this to around CHF100 in the coming years, making its system more competitive. Its method is headed in that direction as the heat needed to recover the collected carbon dioxide has a much lower temperature - less than 100 degrees Celsius - than that used for other systems, which traditionally operate above the 300-degree mark.

Even if these technologies reach full maturity and become part of the mainstream, no one expects them to solve the problem of global warming.

“It’s not a silver bullet, and shouldn’t be considered as such but only as part of a portfolio of technologies that will become important in the medium to long-term,” said Gebald.

Big bad CO2

Carbon dioxide plays a major role in shaping climate and temperatures. Under ideal circumstances, CO2 is part of the so-called carbon cycle, a neutral process over the longer term. But humans have upset that cycle by using fossil fuels and cutting trees and research has shown that higher CO2 concentrations tend to warm to warm the Earth’s surface.

Carbon dioxide is not the only greenhouse gas, and others such as methane, nitrous oxide and different aerosols also make their way into the atmosphere.

Relatively speaking though they are far less important than carbon dioxide, whose emissions are huge compared to other agents. Its effects can be seen in the atmosphere for much longer as well. Of the total amount emitted now, scientists reckon that 20% will still be in the atmosphere in 1,000 years’ time.

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Capturing CO2

Direct air capture (DAC) concerns technologies that can capture large amounts of CO2 from atmospheric air. The other main technological option for CO2 capture is point-source carbon capture and storage (CCS), which used on flue stacks that emit higher concentrations of carbon dioxide.

The obstacle for DAC is the cost-factor, which needs to drop to be competitive with CCS. According to some studies, the cost is up to ten times higher for DAC. The technology is still largely experimental and some way off from full-scale industrial application, although CCS itself has not been widely implemented so far.

Besides Climeworks, a number of companies are working on DAC, including Carbon Engineering, Global Thermostat, Coaway and Terraleaf to name a few. Many of these firms are start-ups building on earlier academic research. Scientists at Columbia University, the Georgia Institute of Technology, and the University of Southern California are also carrying out further research.

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Such a realisation might come sooner rather than later. The concentration of CO2 in the atmosphere is steadily increasing and has reached a record level, as the World Meteorological Organisation points out in its most recent Greenhouse Gas Bulletin. This is a development which the international community does not seem to be able to stop.

“Progress at a global level is slow”, says the Centre for International Climate and Environmental Research in Oslo (CICERO). “Currently”, the Norwegianexternal link researchers point out, “the world is further away from reaching a solid international agreement on climate than it was 15 years ago, when the Kyoto Protocol was adopted.”

Speaking at the UN’s climateexternal link summit in New York on September 23, Swiss energy minister Doris Leuthard warned that “too little has changed in the world in regard to climate”.

Blocking out the sun’s rays

Climate engineering actions fall into two main categories: carbon dioxide removal (CDR), and solar radiation management (SRM). The first approach involves manipulating ecosystems with a view to increasing the amount of carbon dioxide absorbed by the earth’s biomass: plants, the land, and the sea. For example, spreading iron sulphates on the surface of the ocean stimulates the growth of algae, which bind CO2 by means of photosynthesis. More innovative solutions include using “vacuum cleaners” to filter the carbon dioxide in the air, a field in which some Swiss projects are to the fore (see sidebar).

The SRM approach involves installations in outer space, but also increasing the reflectivity of the earth’s surface, clouds and atmosphere. “By changing the colour of asphalt from dark to light, it is possible to bring about cooling locally, in a city for example. This could prevent hundreds of deaths during heatwaves. Whether it can be done on a large scale is another question”, notes Honegger.

Among the SRM approaches thought most promising is the release of aerosols into the stratosphere using aircraft, missiles or balloons. “You get the same effect as a volcanic eruption”, explains Reto Knutti, a professor at the Institute of Atmospheric and Climate Science, ETH Zurich.

Aerosols such as sulphur particles are released into the atmosphere to form a kind of umbrella deflecting the rays of the sun.


“It is well known”, he goes on, “that after an eruption like at Pinatubo, the temperature goes down.” The dust released by the volcano in the Philippines in 1991 brought down the earth’s temperature about half a degree for two years.

Yet when the option of climate engineering – which for now is confined to projects on a small scale or in a laboratory setting – comes under consideration, crucial questions arise, which Knutti sums up as follows: “What are the collateral effects? And what are the political and ethical implications?”

Uncertainties remain

It is evident that manipulating the atmosphere would cause large-scale changes, in particular  the cycle of water and rainfall, Knutti points out. His colleague at ETH Zurich, Ulrike Lohmann, explains that if aerosols are dispersed into the atmosphere there is less sunlight reaching the earth’s surface, which means changes for the planet. “The result is less rainfall globally, as was found after Pinatubo.”

Climate engineering would change our relationship with nature completely and cause distrust among nations, according to James Fleming, a historian of science and technology and the author of “Fixing the Sky”, a book on attempts to control climate. “The Scandinavians might suddenly say that England is responsible for their bad weather, and vice versa. The potential for future conflicts is enormous”, he has claimed in an interview with Greenpeaceexternal link.

Here is another problem: what would happen if for political, economic or scientific reasons a geo-engineering project was suddenly stopped 20 or 30 years later? “The risk would be a sudden warming of 1 or 2 degrees, even within a single year”, answers Knutti. That would mean an increase in temperature much faster than the current rate, which might have disastrous consequences.

Opponents of climate engineering, who include environmental organisations, say that this whole approach risks distracting our attention from the task of reducing emissions, thus compromising international negotiations. Geo-engineering, they point out, does not attack the problem at its root, but just tries to alleviate the symptoms.

More thought required  

A large part of the scientific world is accordingly sceptical, or at least cautious. At the Berlin conference, Mark Lawrence, scientific director of the Institute for Advanced Sustainability Studies, Potsdam (Germany), expressed his concern that “none of the climate engineering approaches can be implemented rapidly or without problems”.

To grasp the potential, the limits and the collateral effects, we need deeper thought on climate engineering, Honegger believes. This discussion, he adds, should also involve public opinion.

Changing weather and climate – some examples 

1877: An American researcher proposes changing the direction of the Kuroshio oceanic current through the Bering Strait. Purpose: to increase Arctic temperatures by around 15°C.

1929: A German physicist proposes installing giant mirrors on a space station to concentrate solar radiation on the Earth's surface and make the extreme north of the planet inhabitable.

1945: According to the Director of Unesco, exploding atomic bombs over the polar regions would lead to a rise in temperature of the Arctic Ocean and climate warming in Northern temperate zones.

1967-1972: During the Vietnam war, the American army inseminates clouds with silver iodide to extend the monsoon season.

1989: An American climatologist believes that might reflect the 2% of sunlight with a missile shield in Earth orbit.

2006: A Dutch chemist proposes injecting sulphur particles in the stratosphere to absorb sunlight and lower the temperature of the Earth.

2010: Researchers at the University of Geneva are able to create artificial rain thanks to a laser capable of condensing water droplets in the atmosphere.

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(Translated from Italian by Terence MacNamee),

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