A spoonful of limestone

In the last blog I mentioned the fact that SRM measures won't have the desired effects of reduced the amount of ocean acidification which is currently increasing.

The acidity of the ocean is currently increasing due to the fact that as more CO₂ is taken up by the oceans the buffering capacity of the oceans decreases making the oceans more acidic. 

In 2008, Harvey conducted a study that investigated the feasibility of enhancing the absorption of CO2 from the atmosphere by adding calcium carbonate (CaCO3) powder to the ocean. 

Rau and Caldeira (1999), Caldeira and Rau (2000), and Rau et al. (2007) first suggested this idea. They suggested reacting captured fossil fuel CO2 with limestone in reaction chambers on land before releasing it into the ocean, rather than directly injecting captured CO2 into the deep ocean, as in the conventional ocean carbon sequestration concept (IPCC, 2005). However their scheme avoids the impacts on ocean acidity and the eventual outgassing of about 15% of the injected CO2 that would occur with conventional oceanic carbon sequestration but would require large infrastructure efforts.

However Harvey's method would have the desired outcome of partially reversing the acidification of the ocean and the resultant decrease in calcite supersaturation resulting from the absorption of anthropogenic CO2. 

He states that CaCO3 could be added to the surface layer in regions where the depth of the boundary between supersaturated and unsaturated water is relatively shallow (250–500 m) and where the upwelling velocity is large.

The CaCO3 would dissolve within a few 100 m depth below the saturation horizon, and the dissolution products would enter the mixed layer within a few years to decades, facilitating further absorption of CO2 from the atmosphere based upon a study done by Broecker and Takahashi in 1978. 

This absorption of CO2 would largely offset the increase in mixed layer pH and carbonate supersaturation resulting from the upwelling of dissolved limestone powder (Wunsch and Heimbach, 2000).

Harvey later goes on to conclude that Geographically optimal application of 4 billion t of CaCO3 a-1 (0.48 Gt C a-1) could induce absorption of atmospheric CO2 at a rate of 600 Mt CO2 a-1 after 50 years, 900 Mt CO2 a-1 after 100 years, and 1050 Mt CO2 a-1 after 200 years. 

Those statistics prove promising however there are large caveats which can be placed on a scheme like this which I will discuss later.

Thanks again,

Sam.

Icarus

In my previous post, I mentioned the James Bond Villain-esque 'mirrors in space' idea. Here's a clip from the quite frankly awful James Bond Movie Die Another Day, where the antagonist Gustav Graves uses a mirror (called Icarus..... my cliché alarm just went off) to reflect the Sun's light back to Earth. The geoengineering principal is the same but obviously reflecting the light away from Earth.

Enjoy! (I use that term very very loosely!)

Two-Piece Suites

There are two main suites of geoengineering:

Carbon Dioxide Removal (CDR)

The first group of geoengineering options that I'm going to discuss are based upon the engineered removal of CO₂ from the atmosphere by enhancing land or ocean carbon sink or creating new carbon sinks (Keith, 2000).
However for any CDR option, the effects will decay over time due to natural responses of carbon reservoirs to atmospheric perturbations; it will also decay if carbon storage is not permanent (Lenton and Vaughan, 2009). 
Lenton and Vaughan go on to propose that in the long-term, the only way to return atmospheric CO₂ to pre-industrial levels is to permanently store (in some combination of the crust, sediments, soils, ocean, and terrestrial biosphere) an equivalent amount of CO₂ to the total emitted to the atmosphere. 

Solar Radiation Management (SRM)

The other side of geoengineering ideas seek to rectify the increasing radiative forcing caused by anthropogenic greenhouse gas emissions by reducing the amount of solar radiation absorbed. Some proposals range from the wildly ridiculous and James Bond Villain-esque mirrors in space and other ideas which reduce the amount of solar radiation reaching the top of the atmosphere. The other proposals centre around increasing the reflection of shortwave radiation (albedo) within the atmosphere or at the surface (Keith 2000). 
Generally a doubling of atmospheric CO₂ and the radiative forcing increase which comes with it (3.7 Wm−2) is taken as the target to counteract, although actual anthropogenic radiative forcing will continue to vary over time. Each individual idea has specific merits and drawbacks (NAS 1992; Keith 2000; Schneider 2008; Boyd 2008), which will be outlined in later blog posts. 

However.....

The SRM range of ideas do pose some problems; in particular, reducing incoming solar radiation does not ameliorate ocean acidification caused by rising atmospheric CO₂. Indeed successful planetary cooling would be expected to increase ocean CO₂ uptake, thus amplifying ocean acidification (Matthews and Caldeira 2007). 

That's it for now, take care...

More Design for Change

Just a quick post:
My previous post 'design for change' caused a little bit of a stir and as a result I was handed some documentation by the head of environmental services at Laing O'Rourke detailing their carbon emission efforts.
As a company they've set up the Engineering Excellence Group which is an external and internal consultancy group, with one of their main focusses being on cutting carbon emissions. They again backed up their 50% cut in carbon emissions statement that I mentioned in the Design for Change post.
One interesting part of this literature was the fact that David Cameron recently visited the London Gateway Port, constructed by Laing O'Rourke which used the low carbon DfMA approach. He went as far as to say the project was an "emblem of ambition". If projects like this are gaining the political thumbs up, then perhaps in the near future we will see other companies adopting this approach with full government backing.
Hopefully with this sort of recognition it will start a trigger of ambition in other sectors too and start the ball rolling into a green and sustainable economy.