Can space mirrors save the planet?
Listen to the rhetoric surrounding global climate change and you tend to hear words such as ‘mitigation’ and phrases such as ‘limiting the temperature rises’. What you won’t hear is talk of ‘solutions’ or ‘cures’. Such is our dependence on fossil fuels, and such is the volume of carbon dioxide that we have already released into the atmosphere, that climate scientists all agree that significant global warming is now inevitable – the best we can hope to do is keep it at a reasonable level, and even that is going to be an uphill task.
At present, the only serious option on the table for doing this is cutting back on our carbon emissions, but while a few countries are making major strides in this regard, the majority are having great difficulty even stemming the rate of increase, let alone reversing it.
Consequently, an increasing number of scientists are beginning to explore the alternatives. And they’re thinking big. From placing giant sunshades in space to pumping sulphates into the atmosphere at high altitudes, the schemes appear limited only by the imagination of the scientists themselves. They all fall under the banner of geoengineering – generally defined as the intentional large-scale manipulation of the environment. According to its proponents, it’s the equivalent of a backup generator: if Plan A – weaning the world off its carbon addiction – fails, we require a Plan B, employing grand schemes to slow down or reverse the process of global warming.
Geoengineering has been shown to work, at least on a small, localised scale. For decades, May Day parades in Moscow have taken place under clear blue skies, aircraft having deposited dry ice, silver iodide and cement powder to disperse clouds.
Many of the schemes now suggested look to do the opposite, and reduce the amount of sunlight reaching the planet. The most eye-catching idea of all, suggested by Professor Roger Angel, an astronomer at the University of Arizona, is a proposal to erect a space parasol system. The scheme – which in 2006 secured a research grant from NASA – would employ up to 16 trillion minute spacecraft, each weighing about one gram, to form a transparent, sunlight-refracting shade in an orbit 1.5 million kilometres above the Earth. The spacecraft would be launched in groups every five minutes for ten years, and could, argues Angel, reduce the amount of light reaching the Earth by two per cent.
The majority of geoengineering projects – which include planting forests in deserts, depositing iron in the ocean to stimulate the growth of algae, or using sea-salt particles to halt rainfall and extend cloud cover – have focused on achieving a general cooling of the Earth. But some look specifically at reversing the melting at the poles, particularly the Arctic, and even more particularly, the Greenland ice sheet. The reasoning is that if you replenish the ice sheets and frozen waters of the high latitudes, more light will be reflected back into space, applying a handbrake to the warming of the oceans and atmosphere.
The concept of releasing aerosol sprays into the stratosphere above the Arctic has been proposed by several scientists. This would involve using sulphur or hydrogen sulphide aerosols to create clouds of sulphur dioxide, which would, in turn, lead to a global dimming. The idea is modelled on historic volcanic explosions, such as that of Mount Pinatubo in the Philippines in 1991, which led to a short-term cooling of global temperatures by 0.5°C. The scheme has been given some credence by Dr Paul Crutzen, winner of the 1995 Nobel Prize for chemistry for his work on the ozone layer, who argued in 2006 that the aerosols could be delivered by artillery, high-flying aircraft or balloons.
Other techniques have suggested bolstering the ice cap by spraying it with water. Using pumps to carry water from below the sea ice, the spray would come out as snow or ice particles, producing thicker sea ice with a higher albedo (the ratio of sunlight reflected from a surface) to reflect summer radiation.
Scientists have also scrutinised whether it’s possible to block the ice fjords of Greenland with reinforced high-tension cables, preventing icebergs from moving into the sea. However, Veli Albert Kallio, a Finnish scientist and Fellow of the Royal Geographical Society (with IBG), says that such as idea is impractical, because the force of the ice would ultimately snap the cables and rapidly release a large quantity of frozen ice into the sea.
However, Kallio believes that the sort of cables used in suspension bridges could potentially be used to divert, rather than halt, the southward movement of ice from Spitsbergen. ‘It would stop the ice moving south, and local currents would see them float northwards,’ he says.
A number of geoengineering ideas are currently being examined in the Russian Arctic. These include planting millions of birch trees: the thinking, according to Kallio, is that their white bark would enhance the albedo effect, and the loss of their leaves in winter would enable the snow to reflect radiation. In contrast, native evergreen pines tend to shade the snow and absorb radiation.
Using ice-breaking vessels to deliberately break up and scatter coastal sea ice in both Arctic and Antarctic waters in their respective autumns, and redirecting Russian rivers to increase cold water flow to ice-forming areas, could also be used to slow down warming, Kallio says. ‘You would need the wind to blow the right way, but in the right conditions, by letting ice float free and head north, you would enhance ice growth,’ he says.
Stumbling blocks
But will such schemes ever be implemented? The Royal Society recently published a ten-month report that concluded that all geoengineering ideas were controversial, and none were without some risk – but they would have to be taken seriously if conventional measures to limit carbon dioxide emissions fail. ‘Geoengineering is not an alternative to emissions reduction,’ says Professor John Shepherd, of the University of Southampton’s National Oceanographic Centre, who chaired the enquiry. ‘Do we need it? Maybe.’
The major counter-arguments to geoengineering are, first, that it’s a ‘cop-out’ that would allow us to continue living the way we do rather than reducing carbon emissions; and, second, even if the schemes do work, would the side effects outweigh the advantages?
Then there’s the dauntingly high maintenance cost and consequences of a technical failure in a world still happily guzzling oil. ‘I think all of us agree that if we were to end geoengineering on a given day, then the planet would return to its pre-engineered condition very rapidly, and probably within ten to 20 years,’ says Dr Phil Rasch, chief scientist for climate change at the US-based Pacific Northwest National Laboratory. ‘That’s certainly something to worry about. I would consider geoengineering as a strategy to employ only for a very short time while we manage the conversion to a non-fossil-fuel economy.’
Generally speaking, those who are most cautious about geoengineering are the scientists involved in the research. Angel says that his plan is ‘no substitute for developing renewable energy, the only permanent solution’. Crutzen added a similar caveat when he published his thoughts on sulphur injections into the stratosphere in the journal Climatic Change, stressing that the technique would be a last-ditch option that ‘should not be used to justify inadequate climate policies’ and ‘that by far the preferred way… is to lower the emissions of the greenhouse gases’.
The US National Center for Atmospheric Research is exploring the feasibility of a range of geoengineering concepts, but has already suggested that the proposal to inject sulphur into the atmosphere might not stop warming of winters in high latitudes and that rainfall patterns across the tropics and the Southern Ocean might be affected.
‘Geoengineering plans to inject stratospheric aerosols or to seed clouds would act to cool the planet, and act to increase the extent of sea ice,’ says Rasch. ‘But all the models suggest some impact on the distribution of precipitation.’
Unintended results
What is also clear is that even ‘successful’ geoengineering wouldn’t return the Earth to its condition before humanity started to interfere. ‘Geoengineering is capable of returning the planet to a globally averaged temperature similar to Earth at pre-industrial greenhouse gas concentrations,’ says Rasch. ‘But all the models suggest that one could not achieve a simultaneous return of the temperature and precipitation of a pre-industrial world.
‘The question is, what are we aiming for? Are we looking to minimise the changes in temperature compared to today or to the climate of 200 years ago? The climate we would end up with in a geoengineered world wouldn’t be the same as either of those.’
Does this matter? ‘The risk with geoengineering projects is that you can “overshoot”,’ says Dr Dan Lunt, from the University of Bristol’s School of Geophysical Sciences, who has studied the likely impacts of the sunshade and aerosols schemes on the climate. ‘You may bring global temperatures back to pre-industrial levels, but the risk is that the poles will still be warmer than they should be and the tropics will be cooler than before industrialisation. There will be unintended consequences – our modelling suggests that El Nińo events will become less extreme, and that could have implications for fisheries.’
To avoid such a scenario, Lunt says the sunshade project would have to operate at half strength; all of which reinforces his view that the best option is to avoid the need for geoengineering altogether. ‘I don’t know any scientist involved in geoengineering who wants to put their plan into action,’ he says. ‘Everyone says there’s a need to do more research.
‘But our efforts to cut carbon and energy use aren’t going well. We may find ourselves in a position where we need a rapid response to global warming. I think it’s quite likely that it will happen at some point.’
The main reason why geoengineering is countenanced by the mainstream scientific community is that most researchers have little faith in the ability of politicians to agree – and then bring in – the necessary carbon cuts. Even leading conservation organisations believe the subject is worth exploring.
‘As yet, we do not see proposals that are more than unreplicated experiments with unforeseeable consequences and side effects,’ says Dr Martin Sommerkorn, climate change advisor for WWF’s International Arctic Programme. ‘But human-induced climate change has brought humanity to a position where we shouldn’t exclude thinking thoroughly about this topic and its possibilities.
‘If, over the coming years, the science tells us about an ever-increased climate sensitivity of the planet – and this isn’t unrealistic – then we may be best served by not having to start our thinking from scratch.’
November 2009
At present, the only serious option on the table for doing this is cutting back on our carbon emissions, but while a few countries are making major strides in this regard, the majority are having great difficulty even stemming the rate of increase, let alone reversing it.
Consequently, an increasing number of scientists are beginning to explore the alternatives. And they’re thinking big. From placing giant sunshades in space to pumping sulphates into the atmosphere at high altitudes, the schemes appear limited only by the imagination of the scientists themselves. They all fall under the banner of geoengineering – generally defined as the intentional large-scale manipulation of the environment. According to its proponents, it’s the equivalent of a backup generator: if Plan A – weaning the world off its carbon addiction – fails, we require a Plan B, employing grand schemes to slow down or reverse the process of global warming.
Geoengineering has been shown to work, at least on a small, localised scale. For decades, May Day parades in Moscow have taken place under clear blue skies, aircraft having deposited dry ice, silver iodide and cement powder to disperse clouds.
Many of the schemes now suggested look to do the opposite, and reduce the amount of sunlight reaching the planet. The most eye-catching idea of all, suggested by Professor Roger Angel, an astronomer at the University of Arizona, is a proposal to erect a space parasol system. The scheme – which in 2006 secured a research grant from NASA – would employ up to 16 trillion minute spacecraft, each weighing about one gram, to form a transparent, sunlight-refracting shade in an orbit 1.5 million kilometres above the Earth. The spacecraft would be launched in groups every five minutes for ten years, and could, argues Angel, reduce the amount of light reaching the Earth by two per cent.
The majority of geoengineering projects – which include planting forests in deserts, depositing iron in the ocean to stimulate the growth of algae, or using sea-salt particles to halt rainfall and extend cloud cover – have focused on achieving a general cooling of the Earth. But some look specifically at reversing the melting at the poles, particularly the Arctic, and even more particularly, the Greenland ice sheet. The reasoning is that if you replenish the ice sheets and frozen waters of the high latitudes, more light will be reflected back into space, applying a handbrake to the warming of the oceans and atmosphere.
The concept of releasing aerosol sprays into the stratosphere above the Arctic has been proposed by several scientists. This would involve using sulphur or hydrogen sulphide aerosols to create clouds of sulphur dioxide, which would, in turn, lead to a global dimming. The idea is modelled on historic volcanic explosions, such as that of Mount Pinatubo in the Philippines in 1991, which led to a short-term cooling of global temperatures by 0.5°C. The scheme has been given some credence by Dr Paul Crutzen, winner of the 1995 Nobel Prize for chemistry for his work on the ozone layer, who argued in 2006 that the aerosols could be delivered by artillery, high-flying aircraft or balloons.
Other techniques have suggested bolstering the ice cap by spraying it with water. Using pumps to carry water from below the sea ice, the spray would come out as snow or ice particles, producing thicker sea ice with a higher albedo (the ratio of sunlight reflected from a surface) to reflect summer radiation.
Scientists have also scrutinised whether it’s possible to block the ice fjords of Greenland with reinforced high-tension cables, preventing icebergs from moving into the sea. However, Veli Albert Kallio, a Finnish scientist and Fellow of the Royal Geographical Society (with IBG), says that such as idea is impractical, because the force of the ice would ultimately snap the cables and rapidly release a large quantity of frozen ice into the sea.
However, Kallio believes that the sort of cables used in suspension bridges could potentially be used to divert, rather than halt, the southward movement of ice from Spitsbergen. ‘It would stop the ice moving south, and local currents would see them float northwards,’ he says.
A number of geoengineering ideas are currently being examined in the Russian Arctic. These include planting millions of birch trees: the thinking, according to Kallio, is that their white bark would enhance the albedo effect, and the loss of their leaves in winter would enable the snow to reflect radiation. In contrast, native evergreen pines tend to shade the snow and absorb radiation.
Using ice-breaking vessels to deliberately break up and scatter coastal sea ice in both Arctic and Antarctic waters in their respective autumns, and redirecting Russian rivers to increase cold water flow to ice-forming areas, could also be used to slow down warming, Kallio says. ‘You would need the wind to blow the right way, but in the right conditions, by letting ice float free and head north, you would enhance ice growth,’ he says.
Stumbling blocks
But will such schemes ever be implemented? The Royal Society recently published a ten-month report that concluded that all geoengineering ideas were controversial, and none were without some risk – but they would have to be taken seriously if conventional measures to limit carbon dioxide emissions fail. ‘Geoengineering is not an alternative to emissions reduction,’ says Professor John Shepherd, of the University of Southampton’s National Oceanographic Centre, who chaired the enquiry. ‘Do we need it? Maybe.’
The major counter-arguments to geoengineering are, first, that it’s a ‘cop-out’ that would allow us to continue living the way we do rather than reducing carbon emissions; and, second, even if the schemes do work, would the side effects outweigh the advantages?
Then there’s the dauntingly high maintenance cost and consequences of a technical failure in a world still happily guzzling oil. ‘I think all of us agree that if we were to end geoengineering on a given day, then the planet would return to its pre-engineered condition very rapidly, and probably within ten to 20 years,’ says Dr Phil Rasch, chief scientist for climate change at the US-based Pacific Northwest National Laboratory. ‘That’s certainly something to worry about. I would consider geoengineering as a strategy to employ only for a very short time while we manage the conversion to a non-fossil-fuel economy.’
Generally speaking, those who are most cautious about geoengineering are the scientists involved in the research. Angel says that his plan is ‘no substitute for developing renewable energy, the only permanent solution’. Crutzen added a similar caveat when he published his thoughts on sulphur injections into the stratosphere in the journal Climatic Change, stressing that the technique would be a last-ditch option that ‘should not be used to justify inadequate climate policies’ and ‘that by far the preferred way… is to lower the emissions of the greenhouse gases’.
The US National Center for Atmospheric Research is exploring the feasibility of a range of geoengineering concepts, but has already suggested that the proposal to inject sulphur into the atmosphere might not stop warming of winters in high latitudes and that rainfall patterns across the tropics and the Southern Ocean might be affected.
‘Geoengineering plans to inject stratospheric aerosols or to seed clouds would act to cool the planet, and act to increase the extent of sea ice,’ says Rasch. ‘But all the models suggest some impact on the distribution of precipitation.’
Unintended results
What is also clear is that even ‘successful’ geoengineering wouldn’t return the Earth to its condition before humanity started to interfere. ‘Geoengineering is capable of returning the planet to a globally averaged temperature similar to Earth at pre-industrial greenhouse gas concentrations,’ says Rasch. ‘But all the models suggest that one could not achieve a simultaneous return of the temperature and precipitation of a pre-industrial world.
‘The question is, what are we aiming for? Are we looking to minimise the changes in temperature compared to today or to the climate of 200 years ago? The climate we would end up with in a geoengineered world wouldn’t be the same as either of those.’
Does this matter? ‘The risk with geoengineering projects is that you can “overshoot”,’ says Dr Dan Lunt, from the University of Bristol’s School of Geophysical Sciences, who has studied the likely impacts of the sunshade and aerosols schemes on the climate. ‘You may bring global temperatures back to pre-industrial levels, but the risk is that the poles will still be warmer than they should be and the tropics will be cooler than before industrialisation. There will be unintended consequences – our modelling suggests that El Nińo events will become less extreme, and that could have implications for fisheries.’
To avoid such a scenario, Lunt says the sunshade project would have to operate at half strength; all of which reinforces his view that the best option is to avoid the need for geoengineering altogether. ‘I don’t know any scientist involved in geoengineering who wants to put their plan into action,’ he says. ‘Everyone says there’s a need to do more research.
‘But our efforts to cut carbon and energy use aren’t going well. We may find ourselves in a position where we need a rapid response to global warming. I think it’s quite likely that it will happen at some point.’
The main reason why geoengineering is countenanced by the mainstream scientific community is that most researchers have little faith in the ability of politicians to agree – and then bring in – the necessary carbon cuts. Even leading conservation organisations believe the subject is worth exploring.
‘As yet, we do not see proposals that are more than unreplicated experiments with unforeseeable consequences and side effects,’ says Dr Martin Sommerkorn, climate change advisor for WWF’s International Arctic Programme. ‘But human-induced climate change has brought humanity to a position where we shouldn’t exclude thinking thoroughly about this topic and its possibilities.
‘If, over the coming years, the science tells us about an ever-increased climate sensitivity of the planet – and this isn’t unrealistic – then we may be best served by not having to start our thinking from scratch.’
November 2009
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