Climate engineering

Prudent plan B or desperate measure?

As things stand, the Earth’s future does not look rosy. Climate scientists say that increasing atmospheric concentrations of greenhouse gases such as carbon dioxide – largely the result of our insatiable appetite for fossil fuels – could push global temperatures up by as much as 5˚C before 2100, leading to rising sea levels and ever more heat waves, droughts and floods. Many experts believe there is no choice but to slash greenhouse-gas emissions, yet the political will to do so is clearly lacking and those emissions continue to rise. This reality means that scientists are beginning to think the previously unthink­able – that we might need to deliberately interfere with the Earth’s climate to bring it back under control.

In a major report issued by the U.S. National Academy of Sciences (NAS) in February, a panel of 16 scientists underlined the continued importance of cutting emissions. Tinkering with the global climate now would be “irrational and irresponsible”, they insisted.

Even so, they argued that potentially “unmanageable and irreversible” risks associated with climate change make it “prudent” to explore so-called geoengineering or “climate intervention”. Their recommendation raised an immediate howl from opponents of geoengineering, including many environmental organisations, who argued that the risks of massive intervention with nature were simply too high and could potentially lead to conflicts among nations.

Stuart Haszeldine, a geologist at the Uni­versity of Edinburgh, believes that while research can generate useful knowledge it can also bring the object of that research “closer to deployment”. He likens research on solar reflection to nuclear physics: “Once you have discovered how to split atoms and get energy out of them you are on a slippery slope”. He raises the prospect that a rich country deploying aerosols to cool its own territory or increase local rainfall might create drought in another part of the world. “These are fundamental moral questions,” he says. “Scientists alone can’t make those judgements. I think any scientific experimentation needs to be filtered through the prism of society more broadly”.

The NAS report focussed on two approaches: extracting carbon dioxide from the atmosphere and deflecting some of the Sun’s rays away from Earth. These are explained on the following pages.

Approach n°1

Extracting carbon dioxide from the atmosphere

1. One way is to enhance natural processes, such as growing more trees, stimulating rock-mineral weathering, or releasing iron into the oceans so as to boost the growth of carbon-consuming phytoplankton.

2. Another method involves sucking up carbon dioxide using crops specially grown for the purpose, such as corn or switchgrass, and burning these plants in a power station. The CO2 from the power station’s flue gases would then be separated using chemical processes and buried underground (“sequestered”) or else used to extract oil from poorly producing oilfields.

3. Carbon dioxide could be removed directly from the air using large banks of fans to draw carbon-containing air in from the surroundings. Again, the carbon would be separated using chemicals and then sequestered.

Pro: Risks are low and well understood (the one exception being ocean-iron fertilization, which could harm wildlife on the seabed).

Con: These technologies are currently very expensive, perhaps more so than solar power or other renewable energy sources.


Approach n°2

Deflecting some of the sun’s rays away from earth

1. One way would be to disperse sulphur-containing particles in the upper atmosphere, in order to reflect or absorb light that would otherwise warm the surface of the Earth. The sulphur could be delivered using specially adapted aeroplanes, or conceivably via rockets or high-altitude balloons.

2. Alternatively, aerosols sprayed near low-lying clouds over the ocean could serve as nuclei around which water droplets condense, thereby changing the properties of the clouds and making them more reflective. The aerosols might simply be particles of sea salt.

3. Other techniques that are either trickier or less well developed include placing discs, prisms, screens or other reflecting objects in space, as well as painting roofs or streets white or covering deserts in highly reflective materials.

Pro: Sulphur dispersion AND aerosol spraying are technically feasible. They could probably be carried out relatively cheaply, and would have a substantial effect on climate within a decade.

Con: This is environmentally and politically risky. Some experts point out that sulphate particles naturally spewed by volcanic eruptions decrease levels of ozone and can have a major effect on rainfall patterns.

Once begun, such geoengineering would need to be continued for hundreds if not thousands of years – a scale that reflects the lifetime of CO2 in the atmosphere (sulphur dioxide, in contrast, disappears after a few weeks). That could prove devastating if those programmes were suddenly terminated: the pent up warming would then take place in as little as a decade.

Stuart Haszeldine (University of Edinburgh)