Exploring the side effects of geoengineering – experts respond

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Technological fixes to combat harmful effects of climate change — even if employed on a massive scale — will be ineffective in the face of ever-increasing greenhouse gas emissions, new research suggests.

A study from German researchers published this week in Nature Communications found no more than an 8% reduction in warming could result from any of four proposed geoengineering techniques: ocean fertilisation; ocean alkalinisation; artificial ocean upwelling and desert irrigation and reforestation.

The study also found that a fifth method — reflecting solar radiation back to space — could potentially reduce warming more, but involved serious side effects and could not be safely stopped once begun.

Dr Matt Watson, Senior Lecturer in Natural Hazards, University of Bristol, comments:

“This paper’s concluding remarks suggest that climate engineering must not be relied upon as a get out jail free card. It reinforces the conventional wisdom that there is no easy solution and that no one methodology or technology will provide us with a silver bullet. The paper compares several different technologies and, as with previous work, concludes that all are in some way flawed. By the authors’ own admission the models are simplistic and only represent the beginnings of careful research which must go, for example, beyond global mean temperatures. Nevertheless the paper sounds a timely warning about the abject stupidity of relying upon climate engineering solutions when reducing our reliance on carbon-based energy systems is the only sensible option.”

Dr Tim Fox, Head of Energy and Environment at the Institution of Mechanical Engineers, comments:

“The findings of this new paper are a welcome contribution to our understanding of the potential for climate engineering. In particular they highlight the uncertainties inherent in those interventions that focus on managing incoming solar radiation or the manipulation of ecosystems. While potentially altering temperatures and CO2 levels to some degree, when deployed at the scale necessary to compensate for global ‘business-as-usual’ man-made greenhouse gas emissions these approaches are likely to have damaging ecological or environmental side-effects and in some cases prove difficult to control.

“Geoengineering methods that use technology in air capture machines that remove CO2 directly from the atmosphere may prove to be much more viable as a climate engineering component of our response to global warming. The air capture approach tackles the root problem without ecosystem intervention and involves controlled capturing of CO2 from the atmosphere. Once captured the gas can either be buried underground or used as a feedstock for industrial processes that effectively recycle the carbon in a closed loop.

“The paper does however highlight clearly the urgent need to action approaches to climate change that increase mitigation and adaptation efforts, while simultaneously performing rigorous studies of proposed climate engineering methods. Although some climate engineering approaches, including air capture, may prove useful, they cannot be relied on as a ‘silver bullet’ and need to be set in a wider policy framework that puts substantial effort into reducing greenhouse gas emissions and adapting to the future climate change we already anticipate. The flooding and widespread infrastructure failures caused by the UK storms of the past few weeks have emphasised the urgent need to increase our preparedness and resilience to the types of changes we anticipate in the coming decades.”

Prof John Shepherd, Professorial Research Fellow in Earth System Science, University of Southampton, said:

“This is a useful paper that confirms and fills in some extra detail of what we already knew, i.e. that geoengineering is not a magic bullet, and that “the safest and most predictable method of moderating climate change is to take early and effective action to reduce emissions of greenhouse gases” (Royal Society 2009).

“The paper contains little that is really new, and it does not show that the side-effects of geoengineering would be worse than the effects of un-moderated climate change, except in the case of rapidly terminated Solar Radiation Management (a well-known result) and enhanced ocean upwelling.

“Only selected methods of greenhouse gas removal are considered, and all involve directly modifying the Earth’s chemical or biological systems (unlike Direct Air Capture, which is not considered), so it is no surprise that there would be some serious side-effects.

“The paper’s conclusion, that “the potential for these types of climate engineering to make up for failed mitigation may be very limited” simply confirms what is known already.”

Dr Tim Kruger, James Martin Fellow, Oxford Geoengineering Programme, University of Oxford, comments:

“The paper emphasizes that proposed climate engineering (also known as geoengineering) methods “should not be solely counted on to prevent warming or large-scale changes to the Earth system”. The study looks at the potential effectiveness of several proposed methods set against the background of a high-emission scenario – RCP8.5.

“The paper makes a useful contribution in considering the impact of five proposed geoengineering methods (four of which act to reduce the amount of CO2 in the atmosphere and one which reflects a proportion of the sun’s radiation back into space) and assessing these methods using an Earth system model to predict their effects on temperature and CO2 levels. It also considers what side-effects are likely to occur and what impacts withdrawing deployment of such methods would have.

“The conclusions of the study are that the methods that remove CO2 from the atmosphere would, even if applied at massive scale, make only a small dent in temperature changes that would occur in a high emission scenario and that while the proposed method of reflecting a proportion of the sun’s radiation back into space has the largest potential for preventing warming, that method ‘has some of the largest side effects and cannot be discontinued without causing rapid climate change’.

“The study looks at RCP8.5 – the highest of the four Representative Concentration Pathways considered by the IPCC – thus creating the most testing circumstances. It would be interesting to run this study for RCP4.5 and RCP6.0 scenarios.

“Another useful study would be to include Biomass Energy and Carbon Storage (BECS) – a method which is already assumed in many of the models that reflect the RCP2.6 scenario. Indeed it is only with massive amounts of BECS that such models are able to avoid ‘dangerous’ climate change (>50% probability of global mean temperatures peaking below 2C above pre-Industrial levels).

“The paper also recognises that the implementation of such proposed methods is constrained not only by technical and environmental constraints (considered in this paper) but also by governance and ethical issues (not considered in this paper). The authors conclude that “the potential for these types of climate engineering to make up for failed mitigation may be very limited”. It is important, however, to note that there are proposed methods beyond those examined and indeed there will be many more proposed methods in the years ahead. It is clear that none of these proposed methods is a ‘silver bullet’, but it may be that, in conjunction with increased mitigation, we may be able to develop ‘silver buckshot’ which could halt climate change in its tracks.”

Dr Peter Irvine, Research Fellow, Institute for Advanced Sustainability Studies (IASS), comments:

“This study, along with many others, finds that CDR (carbon dioxide reduction) methods could not replace mitigation but that they may be of some help. Many approaches to mitigate CO2 emissions are safe, relatively cheap, and available today unlike many of the proposed CDR technologies, some of which may carry large environmental risks, and many of which may be prohibitively expensive or simply infeasible.

“If an effective SRM (solar radiation management) technology can be developed then it could cool the climate but would certainly not solve all the problems associated with rising greenhouse gas concentrations, as the climate would still change and the oceans would still acidify. The authors show that if SRM were terminated, the planet would rapidly warm and that some of the stored CO2 would be released from the land biosphere.”