A paper published in Nature Communications
last month prompted me to revisit two of the Institution’s 2009 reports on tackling climate change: “Geo-engineering: Giving Us The Time to Act?"
and “Climate Change: Have We Lost The Battle?”
The term ‘geo-engineering’ has now largely been replaced by ‘climate engineering’.
These 2009 publications tentatively considered the potential 'emergency' deployment of Solar Radiation Management (SRM) techniques as a possible approach to tackling future climate change. SRM geo-engineering involves reflecting solar radiation back into space on a large-scale. This would intervene in the Earth's heat balance, thereby preventing global mean temperatures rising in response to increased greenhouse gas (GHG) concentrations in the atmosphere.
Schemes could include placing mirrors in space or injecting particles, such as sulphur, into the stratosphere to form reflective aerosols, effectively mimicking the effects of volcanic eruptions. From an engineering perspective, the latter is regarded as the most plausible, both in terms of technical feasibility and potential cost.
Both of the Institution’s reports suggested that SRM might provide a short-term temporary 'emergency' intervention in response to failed mitigation policies. This would be subject to the outcomes of research into whether it could be deployed without detrimental environmental or ecological side effects. The 'emergency' would be a dangerous global mean atmospheric temperature excursion and the use of SRM in response could only be temporary. SRM does not tackle the root cause, that of GHG concentration in the atmosphere, and would only 'mask' the temperature rise until the SRM process was stopped. At this point the excursion would take place anyway. We at the Institution took the view, in the report, that a decision to deploy SRM was unlikely to occur until the 2040s.
Subsequently, a number of research studies have examined both the potential of SRM – in particular the use of reflective aerosols injected in the stratosphere – and its likely side effects. These have been seen to be problematic, including such features as changing rainfall patterns in the tropics.
The findings in Nature Communications are a welcome and pertinent addition to our understanding. In particular, they highlight the uncertainties inherent in those climate engineering interventions that focus on either managing incoming solar radiation or the manipulation of ecosystems. The interventions considered were large-scale afforestation; artificial ocean upwelling; ocean alkalinization; ocean iron fertilization; and SRM. These measures could potentially reduce CO2 levels, or temperatures, or both, to some degree when deployed at the scale necessary to compensate for global 'business-as-usual' GHG emissions. However, these approaches were considered likely to have damaging ecological or environmental side effects and, in some cases, could prove difficult to control.
What the study did not touch upon, was research into interventions that use technology and engineering in air capture machines to remove CO2 directly from the atmosphere. The Institution’s report: Air Capture: Negative Emissions and Carbon Recycling
pointed out that these methods, particularly if powered from renewable sources, may prove useful as a component of our mitigation response to global warming.
The air capture approach tackles the root problem without ecosystem intervention. Instead, it involves controlled capturing of CO2 from the atmosphere. Once obtained, the gas can either be stored underground, as proposed for carbon capture and storage (CCS), or used as a feedstock for industrial processes that effectively recycle the carbon in a closed loop. However, from an engineering perspective, air capture technology is unlikely to be deployable at a scale at which it could be termed effective climate engineering. It would be most valuable as an additional mitigation tool in the suite of approaches available to help reduce GHG emissions.
The new paper in Nature Communications
, along with others published in recent years, answers the Institution's call, in our 2009 reports, for more research to be carried out on these climate engineering techniques. It largely rules out SRM as an option, even in an 'emergency'. Additionally, it acts as a timely reminder of the need to action approaches to climate change that increase mitigation and adaptation efforts if, as a society, we wish to respond. Some proposed climate engineering approaches that use technology and engineering to remove GHGs directly from the atmosphere may prove useful to a degree in the future. However, they cannot be relied on as a 'silver bullet' and need to be set in a wider policy framework: one that puts substantial effort into reducing emissions and, in particular, adapting to the future climate change we already anticipate.
The UK storms of the past few weeks caused flooding and widespread infrastructure failures. These failures have emphasised the urgent need to increase our preparedness and resilience to the types of changes that scientists anticipate in the coming decades.
To read the full research: Potential climate engineering effectiveness and side effects during a high carbon dioxide-emission scenario