Space Sunshades: Time to ditch the sunscreen?

Tomorrow the skies will light up for the New Year’s celebrations across the globe. However, the backdrop to thousands of fireworks displays could look very different in the future if space geoengineering takes off. This is the most direct and technologically reliant SRM, working on the idea that a giant ‘shade’ or ‘mirror’ in space could reflect enough solar insolation to cool the planet quite quickly. It might sound quite drastic, but considering that Znamya 2 space mirror project (directing light towards Earth) launched successfully in the 90s, it appears technically feasible.

The second (failed) experiment of Znamya 2.5 (SRC, 1999). A geoengineering space mirror would be faced away from Earth and reduce solar insolation reaching the Earth.

How big?

Znamya 2 was 20m in diameter and produced a spot of light 5km in diameter. To cool the planet enough to reach the two degree target the space mirrors would need to cover an area of 3 million km² on Earth. This is approximately the size of India, but only 1/55 of the Pacific Ocean. Lior (2013) suggests that the space mirror technology is more likely to be developed for economic gain i.e. for harnessing solar energy and lighting up areas in need e.g. during natural disasters when nightfall hinders rescue efforts. However, this would require facing space mirrors towards the Earth and increasing solar radiation. Lior (2013) does not rule out the idea of turning the mirrors around for geoengineering purposes, but ultimately the geoengineering mirrors would have to offset the impact of the other space mirrors before reducing total solar insolation. This would require a larger area to be covered.

Where?

Space mirrors similar to Znamya, made from a fine (5 micrometre thick) reflective film, which burn up in the atmosphere on descent, may be the easiest to implement. This doesn’t mean it would be the most appropriate solution on such a large scale because they could interfere with existing satellites. Other suggestions include placing reflectors at the L1 point (see diagram) rather than in orbit. This would require huge technological advances, but reduces the direct effect on specific regions because the reduction in solar insolation would be global.

A) Angel (2006) and Caldeira (2013) B) Ecochunk (2012) C) University of Arizona (2006)

Moral Issues

The idea that geoengineering could result in reduced efforts to change our fossil fuel dependent lives is especially an issue for space mirrors. The negative consequences are more likely to result from a general change in the hydrological and biological system, which is not as direct as effects of other geoengineering methods. Morrow (2014) suggests that a reduction in emissions could be justified if geoengineering methods are successful. However, this would not be the case for SRM. Space mirrors would not reduce ocean acidification and any failure in the system could result in a more dramatic global warming effect, so reduced mitigation efforts could be catastrophic.

If the technology could be developed, I don’t think it’s the worse idea we have as a ‘back-up’ option. By no means is this a solution, but more of a way to buy time if warming reaches dangerous levels.

Atmospheric SRM: The sky's the limit?

Solar radiation methods which involve modifying components of our atmosphere in order to reduce the incoming solar insolation is what always sprang to my mind when I first thought of geoengineering. It is potentially the most controversial, because the consequences are the least understood. If one of these methods went wrong the outcome could be devastating, with global implications. So why is it even considered? Ultimately, it would be the ‘quickest fix’ around, with no waiting for carbon to slowly sequester, or technology to be developed. Quite simply, if targets are not met and global temperatures are dangerously high, it could reduce temperatures almost instantaneously. There are two main methods; stratospheric aerosol injection and marine cloud brightening.

Stratospheric Aerosol Injection (SAI)

Aside from the fact that it sounds like a painful procedure, the idea is quite straightforward, aiming to replicate the impact of large scale volcanic eruptions, which produce global cooling. This cooling arises from the impact of aerosols in the stratosphere which reflect solar insolation before it has a chance to reach the surface. Sulphate aerosols are commonly proposed for this method, because they already exist in the stratosphere and are the main component of the volcanically reduced temperatures. The stratosphere starts approximately 10-16km above sea level and extends upwards, with the troposphere extending below this boundary. Due to constant interactions between these two atmospheric layers, the increase in stratospheric aerosols as a result of volcanic eruptions are only temporary, because the atmosphere acts to ‘flush out’ the excess. This would also occur with anthropogenic aerosol injection.

 

Natural cooling of the planet by volcanic eruptions (Ruhlman, 2011)

Longevity issues

One of the main problems with replicating volcanic emissions are the unknown climatic consequences to long term increases in stratospheric aerosols. Heckendorn et al. (2009) suggest the increased duration of aerosols would likely lead to the formation of much larger aerosols because of coagulation and condensation effects. This would result in reduced efficiency over time, because the aerosols need to be a certain (small) size. Therefore, progressively more aerosols will have to be injected into the stratosphere for the same effect.

The Heckendorn et al. (2009) study also highlights the negative impacts on the ozone layer. In their model they found that total ozone (O₃) in the ozone layer was depleted by 4.5%, despite the decrease in halogens (responsible for past ozone depletion), because of changing reactions in the stratosphere in response to extra aerosols. The ozone layer over the tropics and the poles would likely become the most depleted, negatively impacting on communities. Therefore, Preston (2012) suggests a compensation scheme would be required to offset communities which are negatively impacted.

Furthermore, if the programme had to be stopped the atmosphere would act to ‘flush out’ the aerosols, significantly increasing global temperatures. This could occur if the negative impacts start to outweigh the positive impacts or if political issues arise, especially because there are no added benefits to SAI, economic or otherwise.

Marine Cloud Brightening

In the troposphere the main type of SRM proposed is marine cloud brightening. This works on the idea that seeding marine stratocumulus clouds with sea water aerosols will increase the albedo of clouds, the areal extent and the lifespan. Stratocumulus (meaning flattened heap in latin) clouds are the most commonly occurring cloud, rarely produce precipitation and already act to cool the planet. Therefore, the aerosols need to be the right size to avoid forming precipitation and negatively impacting the cloud macrophysics. To offset the radiative forcing caused by double the atmospheric CO₂, 1,500 automated wind powered ships like those in the picture below would be required to constantly seed the clouds. However, changing the clouds will affect regional precipitation patterns and it has been difficult to quantify all the macrophysical responses to cloud seeding.

Cloud brightening ship (MacNeil, 2012)

Public Opinion

Mercer et al. (2011) surveyed public opinion of SRM and found a surprising number in favour of researching or conducting experiments for SRM geoengineering. Over the sample of 3105 people from the UK, US and Canada the general results were in agreement for future SRM use and a confidence in the ability of the scientific community to make this technology safe. Mercer et al. (2011) highlight the main reasons given for not wanting SRM are due to beliefs that the natural environment should be left alone. I found this quite surprising despite the fact that my own mistrust of geoengineering methods originally related to the idea that we shouldn’t ‘tamper’ with the environment any more than we already have.

I find my issues with geoengineering methods, particularly SRM, are more to do with the questions surrounding the uncertainties. Unfortunately, tests and experiments cannot provide conclusive results unless they are completed on a large enough scale. To obtain this scale would mean altering the global climate which crosses the line between testing and implementation. I wouldn’t dismiss atmospheric SRM on this basis but I doubt all the risks could be eliminated, although they could be reduced.  

Solar Radiation Management: Land Based SRM

The previous carbon dioxide removal methods have all dealt with the root cause of climate change. However, solar radiation methods (SRM) take a somewhat different approach; dealing with the effects. Rather than removing greenhouse gases they propose to cool the planet by reducing the amount of solar insolation (radiation from the sun) reaching the Earth’s surface. These methods tend to be cheaper and act quicker than CDR methods but would not address issues such as ocean acidification which directly arise from greenhouse gases.  

The main SRM (Rodas, 2007)

Several methods fall under the SRM umbrella, with the altitude of the method affecting the efficiency. The Royal Society (2009) suggests an SRM in space would need to divert 1.8% of solar insolation in comparison to SRM’s at the Earth’s surface which would need to divert 2% of solar insolation. However, land based SRM is probably the least controversial out of all the SRM.

How could the solar insolation be reduced from the land?

It is more accurate to describe the 2% decrease in solar insolation as being reflected instead of diverted, because this hints at the method; albedo (reflectivity) modification. The overall global surface albedo would need to be increased from 0.31 to 0.32, which does not sound like a lot. This essentially involves making surfaces lighter so they reflect more and absorb less solar insolation, thereby reducing warming. However, as soon as you start look at the Earth’s surface as separate components i.e. those which could be modified and those which can’t, problems become apparent. The infographic shows a general division of the Earth into land and water. Some land surfaces can be modified but the colour of the oceans is difficult to change, and clearly there is a lot of ocean.

Approximate surface of the Earth by water and land mass (Alastair, 2016)

So what could be modified?

A study by Irvine et al. (2011) into the climatic effects of land based SRM grouped the potential land surfaces for albedo modification into three; desert, urban and cropland. The table highlights the values they used from other literature as the inputs for their climate model.  

	Area of Earth's surface	Potential albedo increase
Desert	2%	0.8
Urban	0.29%	0.2
Cropland	3.1%	0.04

Polyethylene-aluminium could be used to cover deserts to produce the largest albedo increase. However, this method is also deemed the riskiest because the local cooling effect caused by the changes in albedo over a large area is sufficient to dramatically change large scale atmospheric patterns. Most notably, reducing precipitation and soil water availability across much of the globe. Therefore, it is dismissed by Irvine et al. (2011) as a potential geoengineering technique, based on the range of unwanted climatic changes produced by their model.

Conversely, urban and agricultural surfaces are more spread out, so the effects aren’t as concentrated over specific areas. Urban surfaces could be lightened by whitening rooves and pavements,, which act to reduce the urban heat island effect. However, this is partially offset by the increased household heating during winter months in response to cooler temperatures. Preferential planting of lower albedo crops could also lower regional surface temperatures, but would not have a huge impact on global temperatures.

Albedo values for different urban surfaces (EPA,2006)

Although these methods are deemed inexpensive to deliver, I do not feel they are sufficient to reduce temperatures, reflecting the conclusions of Irvine et al. (2011). Future research into ocean albedo modification may be more promising in terms of combatting climate change but it is also likely the negative consequences could be higher than changing the land.

 

 

Direct Air Carbon Capture and Storage: Go hard or go home?

With the exception of BECCs, the majority of geoengineering methods have focused on enhancing or replicating a natural process to remove atmospheric carbon. These ‘natural’ processes require global implementation, which has resulted in the issue of ‘planetary scale’ cropping up almost every week. As a result, I find myself consistently remarking on the environmental issues surrounding this large scale and concluding that they could be useful on a smaller scale. However, small scale solutions won’t bring the 400ppm of CO₂ down to pre-industrial levels. So maybe a more direct approach is necessary? This brings me to the last carbon capture method on the list; Direct Air Carbon Capture and Storage (DACs). 

Direct Carbon Capture and Storage does exactly what it says on the tin. Technology is used to remove atmospheric carbon. A system driven by renewable energy removes CO₂ from air when it makes contact with a recycled sorbent  e.g. calcium hydroxide Ca(OH)₂ (the ‘slaked’ lime in last week’s post). The resultant CO₂ is then compressed and transferred to the storage location or used for industrial purposes.  

(The DACs process (Rapp, 2011))

At present, this technology is still in the pilot stage, but it could be scaled up or down to sequester the required amounts of CO₂. DACs can be used anywhere because it is not restricted to an energy production plant (e.g. BECCS) or a certain area of land (e.g. Afforestation). Therefore, DACs could offset power plants, or be scaled down and incorporated into residential housing. However, if a personal DAC machine removed the equivalent emissions of 10 trees per year, this would still fall short of the total household’s emissions (see previous blog: Afforestation and Reforestation ). Although, if all UK households installed a device it would offset a notable portion of emissions. This method particularly opens up the moral issue of geoengineering methods. Realistically, if you knew your emissions were being offset by a machine in your garden, even partially, would you be more likely or less likely to change your lifestyle? Probably less likely.

(How a household DACs machine may look (Chiara, 2014))

Goeppert et al. (2012) provided an assessment of DACs and concluded the main limitations on the potential scale are those imposed by the economy. In theory, it could be rolled out globally, but in reality large investment into the industry and surrounding infrastructure would be needed to make it feasible. Goeppert et al. (2012) suggested costs of US$20-1000 per ton of CO₂, although they note there is ongoing research into cheaper processes and different sorbent materials. Furthermore, it is likely the associated costs with geoengineering technologies will reduce over time as they become more commonplace, but this is very difficult to quantify.

The major issue facing all CDR methods (Nichols, 2011)

From my personal experience, I believe DACs would be met with less suspicion than other CDR methods. We are used to building a direct solution to a problem and inherently want to reduce the impact to us and the environment. If DACs were successfully implemented I think it is likely less effort would be put into mitigating climate change, but it could be a useful stepping stone to a renewable world.