Fig.1 Quote from IAGP showing why stakeholders are important in geoengineering discussions (IAGP, 2014)

Stakeholders

1. The public to favour CDR over SRM - as they become more aware of the pitfalls of solar methods.
2. Though the public largely supported geoengineering, mitigation strategies like scaling-up of renewable technologies are prioritised by the public, NGOs and policymakers.

Considerations

Fig.2 Screenshot from lessons for future practices of upstream engagement (NERC & Sciencewise, 2014)

Fig.3 Case study of how we could govern Arctic geoengineering (blue) existing Arctic Council (green) new international organisation based on Keith et al. (2010) and critiqued and sourced from Parthasarathy et al. (2010)

Conclusions

The past

Vostok ice core records demonstrate a correspondence between temperature fluctuations and levels of greenhouse gases (GHGs) in the atmosphere. A sawtooth pattern of temperature ranges (+2 to -9^o C), concentrations of CO2 (280 to 190ppm), and methane (0.78 to 0.32ppm) from 160,000-year records.  A consequence of the Earth's orbit and for the absorption of CO2 from vegetation and weathering (fig.1). 

Fig.1 Fluctuating temperature, methane and atmospheric CO2 concentrations from air samples in ice cores taken from the Antarctic (adaptations of Sowers and Bender, 1995; Blunier et al. 1997; Fischer et al. 1999 & Petit et al. 1999).

What isn't shown in Fig.1 is the rapid present day increases in GHGs, particularly CO2.  Professor Tim Lenton states, that plants  significantly reduce atmospheric CO2, cooling the planet, but this is inhibited by the rate of anthropogenic-induced GHGs. Natural sequestering cannot keep up with the rate of burning woodlands, fossil fuel processing and peatlands that release stored CO2 and methane (86 times greater than the warming potential of CO2), amplifying warming (fig.2).

- For the interests climate sceptics that argue that CO2 increases lag whilst temperature rises over Antarctica please watch this video.

Fig. 2 Illustration of two positive feedbacks as a result of warming temperatures in the Arctic. A negative feedback would be a cooling in temperature ie. promoting sea ice extent, increasing albedo, radiation reflected and hydroxyl production. The present

Global populations would have to be carbon zero by 2035 if we want to avoid Arctic melting. - Dr Hugh Hunt

Though SRM does not tackle atmospheric CO2 concentrations, multiple studies indicate SRM's massive cooling potential, that may reduce warming and in turn,  reduce the impacts on biodiversity in  tundra biomes. Supported by Applegate & Keller (2015), who state stratospheric aerosol stimulation mitigates the melting of the Greenland Ice Sheet, aiding the growth in sea ice and more importantly thickness during summer. It could, in theory, do the same for the Arctic.

Astrophysicist Steven Desch et al. (2017), proposed that wind turbines on the Arctic sea ice that pump water from below onto the surface, to thicken the sea ice during winter so that in summer ,sea ice does not retreat to the same extent. Simulations suggest that turbines covering 10% of the Arctic ice would result in a meter of thickening per year. And if implemented over the entire Arctic by 2030 a year of adding a meter of ice would revert the Arctic back to present day volume and size. But this simple idea is plagued with issues surrounding:

1. Freezing seawater and promoting growth of old ice and not new.
2. Estimated cost of  $500 billion (£400 billion).
3. Logistics of shipping 10 million wind turbine pumps and individual weight of 10 tonnes of steel.

It is important to understand that SRM albedo modification is not a new concept. These approaches are often not as extreme, large in scale or  as effective as the construction of solar reflectors or releasing aerosols. But they seem to be working, with minimal negative effects after implementation (Fig.3). 

Fig.3 Screenshot of examples of small-scale SRM methods being applied in real life Ming et al. (2014).

Source: Save the Arctic illustration.

The future

The imbalance between winners and losers, and the unforeseen consequences of environmental and governance issues, means SRM, cannot be used exclusively. Dr Hugh Hunt, states SRM is required if we urgently need to slow melting in the Arctic. But if we are too late and Arctic permafrost starts to thaw then we will need to implement other means to capture billions of tonnes of atmospheric methane released. The debate still exists concerning which geoengineering approach is better SRM or CDR?  Conclusions are blurred, and perhaps policy makers, scientists and societies need to consider a diverse approach to tackling climate change. 

Fig.1 Screen capture analysing the total publications with 'geoengineering' in its title (source: Web of Science [Last accessed: 11/10/17]).

 Why?

The case of stratospheric aerosols

Fig.1 Screen capture analysing the total publications with 'climate change' in its title (source: Web of Science [Last accessed: 11/10/17]).

“It’s just bullshit for them to say: 'We'll have a 2C warming target and then try to do a little better every five years.’ It’s just worthless words. There is no action, just promises. As long as fossil fuels appear to be the cheapest fuels out there, they will be continued to be burned.”

 Atmospheric concentrations of carbon dioxide (CO2) have risen drastically over the past century, ∼280 ppm (pre-industrialisation) to >380ppm (present day). Environmental reconstructions indicate that CO2 (and other GHGS) in the atmosphere are at their highest.

Stimulating the development of geoengineering techniques that remove CO2 from the atmosphere, and counteract anthropogenically driven greenhouse effects and ocean acidification. Known as Carbon Dioxide Removal (CDR) (Fig.2).

Fig. 2 Illustration of CDR approaches that 'suck' carbon from the atmosphere storing elsewhere (source: Sheperd, 2015)

1. Afforestation & Artificial Trees

1. A Global-scale tree planting effort to capture CO2 through photosynthesis - deforestation accounts for the second largest anthropogenic source of CO2 emissions in the atmosphere.
2. Implementing artificial trees, a large, fly-swat shaped construction that absorbs passing air by using a sorbent (sodium hydroxide), results in CO2 in the atmosphere being separated and stored naturally in the Earth.

2. Biochar & Bioenergy 

1. Biochar can be produced through the heating biomass under reduction of oxygen (processes are known as pyrolysis or gasification). Therefore, no CO2 is produced and released into the atmosphere and "carbon negative".
2. Bioenergy is produced alongside biochar and could displace our global fossil fuel usage - the primary source of CO2 in our atmosphere. Aiding in the reduction of other GHGS emissions. The carbon sequestered in biochar is stable (for up to 2000 years) and can be used as a fertiliser.   

3. Direct Air Capture

1. The construction of large machines that extract CO2 directly from the ambient air and sequestered underground or in the ocean. 

4. Iron Fertilisation

1. Roughly 30% of the world's oceans have low rates of primary production because of low iron concentrations. Therefore, the addition of micronutrients particularly iron onto oceans are shown to promote large-scale planktonic blooms that draw down CO2 from the atmosphere via photosynthesis.

5. Enhanced Weathering & Ocean Alkalinity Enhancement 

1. When fresh exposed olivine is in contact with CO2, magnesium carbonate and silicic acid are formed. Stimulating the removal of atmospheric CO2 stored in the rock that can be deposited onto soil or the ocean bed, tackling ocean acidification.
2. Scientists suggest that enhanced weathering and dusting of finely ground minerals over surfaces, enables more CO2 to be sequestered and promote ocean biological productivity, sucking more CO2 in.

Conclusion