CPP Seminar: Should we Engineer the Climate?

31 May 2013


This report was written by Richard Tomsett, BBSRC-Funded CSaP Policy Intern (April 2013 - July 2013)

“Most nations now recognise the need to shift to a low-carbon economy, and nothing should divert us from the main priority of reducing global greenhouse gas emissions. But if such reductions achieve too little, too late, there will surely be pressure to consider a ‘plan B’ – to seek ways to counteract the climatic effects of greenhouse gas emissions by ‘geoengineering’.” – Martin Rees in his foreword to the Royal Society report Geoengineering the climate: science, governance and uncertainty.

Following this quote, Dr Hugh Hunt of Cambridge's Department of Engineering, went on to detail the scale of the problem: CO2 levels have been rising since the invention of the steam engine, with levels now reaching 400ppm. CO2 levels have not been this high for at least the past 800 000 years [1].

Currently, humans produce about 35 billion tonnes of CO2 per year, with no slowing in production over the last decade. The HadCM3-LC model [2] has been used to make projections of atmospheric CO2 levels, given a stop in human CO2 production. These predictions show that atmospheric CO2 levels would remain high for a long period after ceasing CO2 production. Dr Hunt identified two possible geoengineering solutions to prevent catastrophic warming from excess CO2: remove it from the atmosphere – Carbon Dioxide Removal (CDR), or counteract its warming effect by Solar Radiation Management (SRM).

Dr Hunt went on to outline some CDR approaches. CDR involves actively removing carbon dioxide from the atmosphere, which is easiest to do at the source of CO2 emission. However, this solution does not address the need for further CO2 removal. Various methods exist to enable this, but a predicted 10 billion tonnes of carbon would need to be sequestered per year [3]. Current proposed methods for sequestering carbon would not be able to perform this task in the near future. Dr Hunt also pointed out that the infrastructure for moving and storing 10 billion tonnes of carbon every year does not exist, and would need to be developed. He argued that these limitations meant that CDR was not suitable as an emergency strategy, and that SRM needs to be investigated as an alternative or additional measure.

Dr Hunt is part of the SPICE (Stratospheric Particle Injection for Climate Engineering) project. SPICE is looking at the potential for injecting aerosols into the stratosphere in order to reflect solar radiation back into space, as this appears to be affordable, effective and timely – though further safety research is required. This approach mimics the cooling effects of a volcanic eruption.

SPICE’s research questions are:

  1. What particles are both effective at reflecting radiation and safe to use?
  2. How do we deliver these particles to the stratosphere?
  3. What effect would this have on the climate?

The Cambridge-based group are concerned with the second question. Their potential solution is to use tethered balloons floating in the stratosphere, which spray particles pumped up to them from the ground. This has been proposed as the cheapest and quickest method, taking approximately 5 years of development and costing ~£2 billion. Given this short time-frame, Dr Hunt stressed the urgency for more safety research, and expressed frustration at the media’s reporting of their trials.

SPICE SRM overview. Source:

Dr Hunt’s answer to the title question is that we already are engineering the climate by burning fossil fuels, so we should manage the present crisis sensibly, prepare ourselves, and explore all options.

Question and Answer Session

Q: How long until something like this could happen, and until policy makers will actually consider it?
A: It depends on how dramatic climate change is/appears to be over the next few years. It may be out of the hands of policy makers. Some numbers:

- £2 billion per year for the balloons

- Titanium dioxide may be a suitable particle. The proposed method would use 10 million tonnes per year (or ½ teaspoon per person per year)

- The particles reside in the stratosphere for approximately 1 year

Q: Could the particles be distributed by putting them in jet fuel and using the global airline network for distribution?
A: Aircraft fly at ~10km, but the particles would need to be put into the stratosphere at ~20km. This would require high performance aircraft flying specialised flights.

Q: What are the risk factors?
A: The unknown unknowns. For example:

- Will we switch off the Indian monsoon?

- Will there be enough cooling at the poles? If not, sea levels will still rise.

- How will this affect the ozone layer?

- How toxic would the particles be to sea life?

- Will the particles disperse suitably in the stratosphere?

These questions require small-scale experiments to answer, but public perception is a problem.

Q: How are you engaging with policy makers?
A: Westminster is scared of the public’s perception of these kinds of trials. However, local governments appear to be more interested.

Q: Is there a connection between this approach and tropospheric aerosols?
A: “Global dimming” contributes to cooling. Example: temperatures in the USA rose when flights were grounded after the 9/11/2001 attacks because fewer particles from aircraft were in the atmosphere. However, moisture in the troposphere leads to clustering of particles, which are then no so effective for scattering. Titanium dioxide in the stratosphere would not suffer from this problem, though it would be necessary to minimise ionisation to stop particle clustering.

Q: How can academics engage in open policy making? To what extent do ministers want to be influenced?
A: TV will not touch climate change and certainly not geoengineering – decent debate in the media is not available. Starting with local government might be more productive as they seem to be more interested.

Q: Who will champion further research?
A: Telecommunications companies may be interested. There is a potential dual use of the tethered balloons for GPS and mobile phone signals.

Final remark from Puffles the Dragon Fairy: industry lobbyists have direct links to policy makers, and use them. Perhaps it is time for scientists to do the same.


Royal Society report on geoengineering:
David MacKay’s “Without Hot Air” web-site/book:
A Dragon’s Best Friend blog: