Royal Society of New Zealand, 2011

Goal: Evaluate ‘value for money’ of possible geo-engineering responses to climate change


  • High uncertainty
  • Very expensive projects
  • Multi-disciplinary

Outcome: Improved cross-discipline understanding


Efforts to rein in greenhouse gas emissions have been relatively ineffectual and atmospheric levels are rising sharply. In the absence of mitigation, geo-engineering offers opportunities for preventing potentially catastrophic climate-change tipping points. Yet, despite a plethora of suggested schemes, very few have been tested, and there are no national or international policies controlling them.

In March 2011, the Royal Society of New Zealand hosted a workshop exploring possible geo-engineering responses to global climate change.

The Workshop

The workshop was to explore recent research into geo-engineering options including: increasing soil carbon and sequestering biochar, avoiding deforestation, increased mineral weathering, and ocean fertilization. First, these options were discussed, highlighting the uncertainty ever-present in the interconnected and complex air, ground and water processes comprising the earth system.

The 21 participants, who each had a laptop connected to the local wireless network, used 1000minds to capture their individual preferences on a range of criteria. This information was then immediately presented back to the group to show areas of general agreement and disagreement. The proposals were then rated on the criteria and automatically ranked using the average of the participants’ preferences.


‘Market shares’ for each of the proposals (see below) were also automatically generated and presented to participants. The workshop showed the value of the approach as a tool for fuelling discussion and improving understanding across the wide range of disciplines represented and as a tool that could be used to guide research investment.

  1st 2nd 3rd
Planting trees 50% 6% 11%
Cool roofs 18% 25% 6%
Atmospheric carbon capture 17% 14% 28%
Sunshades in space 9% 19% 11%
Biochar 6% 0% 6%
Cloud whitening 0% 12% 3%
Stratospheric aerosols 0% 10% 3%

“Market share”: Percentage of participants for whom each proposal was ranked 1st, 2nd, 3rd.

Value for Money

In addition, the performance of each geo-engineering response on the range of criteria considered (mentioned earlier) was aggregated into a ‘total score’, ranging from 0 (hypothetically worst) to 100 (hypothetically best), and compared against an estimate of each response’s cost – and presented in the following Value of Money (VfM) Chart.

Clearly, the focus of attention is in the VfM Chart’s top-left quadrant – ie. high Total score (Benefit) and low Total net cost. Possible tradeoffs are along the blue line, the ‘Pareto (efficiency) frontier’: higher Cost can be ‘compensated for’ by higher Benefits.

Value for money chart

[Note: for confidentiality reasons the data presented here have been altered.]


An underlying theme during the workshop was that none of the possible geo-engineering responses is universally acceptable, and that mitigation – reducing greenhouse gas emissions – is still the top priority. There is an urgent need for global regulations to allow for further research, and there should be a moratorium on commercial geo-engineering developments until they are better understood.

See also

News about the workshop