Geoengineering is one of the most discussed and
contentious topics within climate change mitigation. The methods can range from
extremely elaborate, like placing large mirrors into orbit, to more feasible techniques,
such as whitening buildings.
What is
geoengineering?
Geoengineering refers to a “deliberate and large-scale
intervention in the Earth’s climatic system with the aim of reducing global
warming” (Stilgoe, 2015). The
approaches tend to be able to split into one of two broad categories: carbon
dioxide removal or solar engineering (Caldeira et al., 2013).
Solar engineering
(SE)
In summary, solar engineering is decreasing the amount of
solar radiation absorbed by the Earth in order to counter the additional
radiative forcing generated by increased GHGs concentrations in the atmosphere –
to offset the forcing from a doubling of CO2, approximately 1.7% of
the incoming sunlight (Caldeira et al.,2013). These techniques (Figure 1) tend to be large-scale and would be expensive to
implement, and include ideas such as sending mirrors into orbit or injecting
aerosols into the stratosphere.
Figure 1. Summary of different SE approaches. Source: Caldeira et al., 2013 |
It is generally accepted that such methods could be
successful in reflecting sunlight, but the resulting effects are unknown, and
in some locations the techniques could worsen the problem of climate change (Caldeira et al., 2013).
Carbon dioxide
removal (CDR)
Focussed on alleviating the actual cause of anthropogenic
climate change by removing CO2 from the atmosphere. In comparison to
solar engineering, these techniques (Figure 2) are generally of a smaller scale and can be
applied more locally. They include approaches such as reforestation, enhancing
weathering, or fertilisation of the oceans (Caldeiraet al., 2013).
Figure 2. Summary of CDR approaches Source: Caldeira et al., 2013 |
Whilst being typically cheaper and less controversial to
implement, CDR methods tend to be slower-acting and so do not present a
solution on the short timescales that are necessary to reduce the impacts of
climate change.
Comparison of
methods
As mentioned above, the offerings from the two streams of
approach are largely opposite. SE methods are expensive, controversial, would
require international backing to implement, but would be able to reduce warming
within years of introduction. CDR would take longer to take effect and so do
not offer an immediate solution to global warming, but they are more
inconspicuous, usually cheaper (on smaller scales) and are, in most cases, more
localised, allowing for independent introduction by individual countries. There
are exceptions to this, of course, with ocean fertilisation being a prime
example. As seen in Figure 2, this offers significant carbon removal (up to 200
Pg C by 2100), but the most could be almost as controversial as SE techniques;
for example, ocean fertilisation could have dramatic effects on coral reefs and
would be expensive (Caldeira et al.,2013).
In my opinion, there seems one fundamental difference between
SE and CDR approaches, and it’s connected to the issue that is essential to
successfully reducing emissions and mitigating climate change. Whilst solar
techniques are generally the more novel of the two, they represent the problem
that has underlain the failures of action against climate change so far. They
are effectively shifting the responsibility of dealing with our emissions to
another source: rather than remove the issue that we have caused, they instead
focus on altering the Earth system in an even more dramatic way.
I understand, however, that CDR techniques are not
obviously not perfect. To implement them on the scale required would
financially infeasible, and the response would likely not be rapid enough to
solve fast-acting climate change. Limitations of warming to 2oC by
the Paris agreement include geoengineering within them already, and so it must
be assumed that they will eventually be introduced in some capacity. To me, the
best solution would be a combination of the less controversial techniques from
both sets. Biomass energy with CO2 sequestration involves the
capture of CO2 from power plants running on biomass, allowing of
permanent removal of CO2 from the atmosphere. 3% of the global land
area used for this purpose would lead to a reduction of 1 Pg C each year (Caldeira et al., 2013). From the SE
approaches, enhancing solar albedo by installing white roofs globally has been
modelled to reduce daily high and low temperatures in urban areas by 0.6oC
and 0.3oC (Caldeira et al.,2013). By introducing a large quantity of smaller initiatives, we may be
able to produce some significant temperature and CO2 reductions. I
believe the large-scale SE techniques offer a safety net that should only be
used as a last resort, in the failure of other methods.