Carbon Dioxide Removal techniques, such a reforestation and afforestation, were deemed to be the least risky, though slower, than other techniques. Photo: Trees for the Future via flickr.
Saying that "man-made climate change is happening and its impacts and costs will be large, serious and unevenly spread, the Royal Society's new paper "Geoengineering the climate: science, governance and uncertainty" [PDF] lays out the case for the necessity for greater consideration of geoengineering schemes as humanity's backup plan, in case emission reduction efforts fail:50-50 Chance Emissions Reductions Will Be Enough
The year-long study says, "global efforts to reduce emissions have not yet been sufficiently successful to provide confidence that the reductions needed to avoid dangerous climate change will be achieved."
According to lead author John Sheppard, right now we've got a 50-50 chance to that emissions reduction alone will work to keep global average temperature rise below 2°C. Sheppard says, "We are already staring 1.6°C in the face." (New Scientist) Therefore we need a two-part backup plan to cool the planet.
Carbon Dioxide Removal Techniques
One part would be Carbon Dioxide Removal techniques: These address the root cause of climate change, and do so with lower risk on unintended consequences, but work more slowly. We're talking proposals such as CO2 scrubbing "trees" and reforestation/afforestation programs here.
Solar Radiation Management
The other part is deploying some sort of Solar Radiation Management to quickly reduce global temperatures. Pumping sulphate particles into the atmosphere was identified as the most cost-effective method, but one which would do nothing to curb ocean acidification or other side effects of increasing greenhouse gas emissions -- the report acknowledges that this could have other unintended side effects as well.
Geoengineering Proposals Only Come After Emissions Reductions
In conclusion, the report recommends that nations make increased efforts to reduce emissions (at least 50% below 1990 levels by 2050) as the first step. Past that, more research is needed into geo-engineering techniques, with geo-engineering only being considered as part of more comprehensive efforts to reduce emissions and Carbon Dioxide Removal being preferred to Solar Radiation Management.
Royal Society Ranks Geoengineering Techniques
As far as the Carbon Dioxide Removal techniques with the most potential: Capturing CO2 from ambient air (preferred, but not cost-effective yet); enhanced weathering, and reforestation/afforestation were ranked highly -- though the last was seen to be limited by land use conflicts.
Those CDR techniques with the least potential: Biochar ("significant doubts" about scope, effectiveness and safety - "substantial research" required to prove effectiveness) and ocean iron fertilization (not proven to be effective and "high potential for unintended and undesirable ecological side effects").
Read the full report: Geoengineering the climate: science, governance and uncertainty [PDF]
UPDATE: Clarified position of Royal Society on effectiveness of CDR techniques.
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