Geoengineering: Can it help our planet keep its cool?
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This topic is sponsored by the Australian Government Department of Climate Change and Energy Efficiency.
Geoengineering might cool the Earth, but at what cost?
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In 2007, the California-based firm Planktos announced a proposal to dump tonnes of finely-ground iron into the ocean near the Galapagos Islands. The idea was that since much of the ocean is nutrient limited, increasing the iron content of the water would encourage marine algae to bloom. These extra algae would take up carbon dioxide through photosynthesis, turning back some of the threat of climate change. Investors in the scheme would be able to claim carbon credits for the removal of carbon dioxide and to offset those reductions against other carbon dioxide generating activities.
The project was, and remains, very controversial. Supporters called it an economically-viable technical fix for a serious environmental problem. But many damned it as marine pollution with unforeseeable consequences. However, it did serve to focus attention on the concept of geoengineering as one possible way to tackle the challenge of global warming. That too is much argued.
In the end, the Planktos proposal did not proceed, partly at least because it could not raise the necessary capital. But the geoengineering debate continues.
temperatures dropping by 0.5°C
(Image: USGS)
Geoengineering: The answer to climate change?
Geoengineering (otherwise known as climate engineering) is a branch of science which is focused on applying technology on a massive scale in order to change the Earth's environment. At the moment many geoengineering technologies are considered hypothetical and risky, but they are being increasingly promoted as a way to reduce the effects of global warming arising from greenhouse gas emissions.
Based on the well-accepted science of climate change (Box 1), there are two potential ways that geoengineering might help us face the threat of global warming (Box 2).
We could try to pull some of the accumulated greenhouse gases (especially carbon dioxide) out of the air. Less greenhouse gases would mean less warming.
The alternative is to try to reduce the level of the Sun’s incoming energy to reduce the Earth’s warming. For example, we could increase the amount of sunlight-reflecting clouds and aerosols present in the atmosphere. This already happens naturally when clouds reflect some of the incoming sunlight back into space, slightly cooling the Earth’s surface beneath. From time to time, volcanic eruptions do much the same thing by throwing clouds of gas and dust high into the atmosphere. After large eruptions we usually see a small short-lived drop in global temperature over a year or two until the dust has gone.
Both approaches could have unexpected consequences. However, geoengineering advocates argue that if we fail to reduce greenhouse gas emissions, geoengineering might well be part of the mix of solutions that we will need to apply to tackle the challenges of climate change. There is also a risk that we have underestimated the rate of climate change and its consequences for the biology of the world.
How might geoengineering strategies work?
Carbon dioxide removal (CDR)
- The ocean fertilisation strategy, discussed earlier, is one idea for removing carbon dioxide, but there is still scientific uncertainty surrounding its likely success and that of similar proposals (such as ocean upwelling, which brings deep, nutrient rich water to surface levels to stimulate phytoplankton growth). Many small-scale experiments have been conducted around the world, including by Australian scientists, to demonstrate the response of surface ocean biology to fertilisation. For example, a co-sponsored study in 2009 by Germany and India (the LOHAFEX trial) into the effects of iron fertilisation in the south-western Atlantic Ocean, did not give any real support to the technique. It underlined the complexity of ecosystems, and the hazards of tinkering with them. Unexpected marine species bloomed and local carbon dioxide levels were little affected.
A dust storm that dumped thousand of tonnes of nutrient rich topsoil into Sydney Harbour during 2009 caused an explosion in carbon dioxide-absorbing phytoplankton. Scientists monitoring the microscopic organisms at the Sydney Institute of Marine Science reported that populations tripled during the event. They estimated that the extra phytoplankton captured around eight million tonnes of carbon dioxide – equivalent to a month’s emissions from a coal-fired power station – and that little long term environmental damage was observed. But whether this removal was largely permanent (with the captured carbon sinking deep into the ocean) or temporary (with the phytoplankton being consumed by carbon dioxide respiring organisms) remains unresolved.
- Plants, particularly trees, take in large amounts of carbon dioxide through the process of photosynthesis. More trees and crops could certainly be planted to take up extra carbon dioxide. The challenge is that many billions would be needed to make a real difference and climate, soils and competing land uses would limit the numbers we could plant. Furthermore, in some regions of the Earth, climate change itself may limit the viability of future forests causing a loss of carbon from the trees and the soils. There is another issue: when a plant dies, carbon dioxide is returned to the atmosphere as it decays. Also, methane (a nastier gas in greenhouse terms) is produced.
- Similarly, reducing deforestation would certainly cut emissions. In some countries current rates of deforestation are releasing carbon dioxide into the atmosphere at rates far greater than from the burning of fuels. A reduction of deforestation would need to be carried out on a massive scale to make any real global difference without other contributions, but at the same time, it may be a comparably achievable method with which to reduce greenhouse emissions.
- When plants die and decompose much of the carbon they accumulated when alive is released to the atmosphere. Through a process called pyrolysis, crop and forestry wastes could instead be converted to a type of charcoal called biochar. This can be ploughed into the ground, which improves the soil and – because it is resistant to microbial decomposition – effectively locks away the carbon for hundreds or thousands of years. Like some of the other geoengineering options, it would need to be undertaken on a very large scale to make any substantial difference to carbon levels. Energy is needed to drive pyrolysis, so there are costs as well as gains.
- Weathering of rocks can remove carbon dioxide from the atmosphere through reactions with minerals to form carbonates. Various ways have been suggested to store carbon dioxide by mimicking this natural process – but at a much faster rate. These are grouped under the heading of enhanced weathering. Enhanced weathering should provide permanent carbon storage and has been described as one of the less risky CDR options. But there remain many questions and challenges, such as how the carbon dioxide could be extracted from the air at an acceptable financial and energy cost, and the environmental impact of storing the end-product in soils or in the ocean.
- Direct absorption of carbon dioxide from the air though chemical or cryoscopic methods is also being investigated. At the moment, such options appear to be very energy intensive and expensive but research into these technologies is ongoing.
(Click for larger image)
Geoengineering schemes to deliberately alter the Earth’s climate.
(Image: adapted with permission from Lawrence Livermore National Laboratory)
Solar radiation management (SRM)
SRM has caused some excitement through the scale and complexity of the technologies. One thing is clear: proceeding with these far-reaching strategies will require careful consideration of the costs and risks versus any benefits. Some of the suggested actions are:
- The ‘cool roof’ strategy. Replacing dark roofs and pavements with light coloured ones could change the albedo (reflectivity) of the Earth, causing more sunlight to be reflected back into space. This is one of the potentially low-cost solutions, and there is a benefit to the home owner, too, since it would cut cooling costs. But hundreds of millions of households would have to take action for any noticeable effect.
Proposals to plant more reflective crop varieties and install reflective surfaces in deserts have a similar aim of increasing the albedo of the Earth.
- Uplifting water vapour to enhance low level clouds. In this scenario, a fleet of custom-built ships would be deployed to vaporise seawater and send it into the lower atmosphere. Proponents expect that more clouds would form, especially over the oceans, and reflect sunlight back into space. As with some other geoengineering methods, it will remain effective only as long as the technology (in this case the fleet of ships) remains in operation. In this case the water would need to be constantly replaced, as it resides in the lower atmosphere for only a few days before raining out.
- Injecting aerosols into the stratosphere. This would imitate the impact of volcanic eruptions, by placing chemical compounds, such as sulfates, into the atmosphere. There they would block light arriving from the sun. The challenge would be to not only inject millions of tonnes of aerosols at high altitudes (presumably from a fleet of high-flying aircraft), but also to maintain the aerosol levels as they slowly fall under gravity. Also needed would be a greater understanding of the potentially far-reaching impacts of stratospheric aerosols.
- Blocking the arrival of sunlight by space-based ‘umbrellas’. Still more spectacular technologically would be the deployment by rockets of many millions of thin reflecting disks into Earth’s orbit to dim incoming sunlight. This could be done quite quickly, but at great cost and with unknown effects on climate and agriculture in different regions.
- Regional modification of cloudiness. Clouds already play a significant role in how much solar energy reaches the Earth’s surface and thus influence global and regional temperatures. Modification of cloudiness through various possible cloud-seeding options could potentially provide some regional control of the climate change. As with the other SRM approaches, such seeding would need to be on-going and the impacts might have unpredicted and undesirable effects. More research is required to ascertain the technical viability, economic costs and possible side effects of such technology.
All avenues at once?
Geoengineering offers a variety of ways to reduce global warming, but each option brings with it enough issues and challenges to suggest that none of them is the demonstrated solution. They vary in cost, risk, effectiveness, time-scale and complexity of regulation. Engineered carbon dioxide removal may be less risky, but will take longer to work. Solar radiation management may lower temperatures effectively and quickly, but doesn’t stop other impacts of climate change. Geoengineering technologies may have unexpected effects on things like rainfall and ecosystems. And, we don’t know the extent to which they could actually work. None can provide a sure, easy and timely fix. Nor is it clear what the cost-benefits of each option are.
(Click for larger image)
Different geoengineering technologies each have their own pluses and minuses
(Image: The Royal Society)
These uncertainties suggest that whilst we need to keep all options open for the future, the number one priority still needs to be reducing the production of greenhouse gas emissions that are central to the problem. This means reducing our demand for energy, using low emission sources of energy, improving our energy efficiency and conservation and reducing land clearing. We know how to implement these strategies already. We already have a good handle on their impacts and even their costs.
However, we need to investigate the use of geoengineering options for use as a last resort. We need to develop the technology and suitable governance strategies should the first rank management options show signs of failing (Box 3. Governing geoengineering). Whatever solutions we choose, they will need to be sustainable, not reliant on the continual maintenance of complex and costly systems. If the latter become our only course, we are in deep trouble.
Boxes
1. Geoengineering and climate change
2. The two types of geoengineering
3. Governing geoengineering
Related Academy Links
Nova
Enhanced greenhouse effect – a hot international issue
Warmer and sicker? Global warming and human health
Getting into hot water - global warming and rising sea levels
Capturing the greenhouse gang
Carbon currency – the credits and debits of carbon emissions trading
Acid test for the seas
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Australian Academy of Science.
Posted February
2010, edited August 2012.