Anthony Doesburg: Absorbing ideas to combat warming

Artificial trees to absorb carbon dioxide and wind turbines line a motorway in this artists's impression of technology that could combat climate change, as suggested by the UK Institution of Mechanical Engineeners.

Engineers are famously practical people. Scientists, for their part, are exhaustive seekers of new knowledge - sometimes based on a hunch, but always thoroughly tested before being added to the sum total of human wisdom. In theory, anyway.

On that basis, while scientists continue to collect data about climate change, engineers might be expected to apply what we already know to trying to solve the problem.

American physicist Freeman Dyson - labelled a climate change heretic because he thinks the world faces more pressing problems - summed up their different approaches to life, saying: "A good scientist is a person with original ideas. A good engineer is a person who makes a design that works with as few original ideas as possible."

Maybe so. But a report last month by the British Institution of Mechanical Engineers (IMechE), on how to stave off the effects of global warming, can't be accused of lacking originality.

The body, which boasts 80,000 members and a history that pre-dates the invention of the internal combustion engine, is proposing three novel ways of buying some time before measures are put in place to reduce carbon dioxide emissions.

One of their ideas, coincidentally, echoes a suggestion of Dyson who, even though he doesn't believe global warming is bringing the planet to the brink, acknowledges that humans are pumping more and more carbon dioxide into the atmosphere. It's nothing that planting a trillion trees wouldn't cure, the self-proclaimed scientific subversive has said.

Whereas Dyson's trees would be specially bred to consume lots of carbon, the British engineers are recommending artificial ones - 100,000 of them at an estimated cost of US$20,000 ($29,000) each - to capture all of Britain's "non-stationary and dispersed" emissions, at a rate of about 10 tonnes each a day.

Sorbent (able to collect molecules of another substance) material on the trees' "leaves" would make them several thousand times more effective at removing carbon dioxide than any natural tree, according to the report. The carbon dioxide would then be stored, most feasibly in depleted oil and gas reservoirs.

Non-stationary and dispersed emissions make up about half of the global total, the report says. With a fifth of all emissions coming from the transport sector, the logical place to plant artificial trees would be along motorways.

With that would come visual pollution on a similar scale to wind farms, to which there is already significant opposition. Another of the ideas for soaking up carbon dioxide is less intrusive and could even become an architectural statement.

The engineers suggest incorporating photobioreactors - PBRs, or sealed vessels containing carbon dioxide-absorbing algae - into building structures. Algae growth is fuelled by carbon dioxide, through photosynthesis, producing energy that could be used for building light and heat.

The engineers say algae's energy content by weight is greater than wood and rivals coal. As well, the by-product of refining algae, biochar, could be used as fertiliser. The PBRs, which could be prefabricated and fixed to new or old buildings, would also provide insulation.

The algae-coloured tubes fixed vertically or horizontally to the outside of buildings, where they are exposed to maximum sunlight, could become striking architectural features. And using buildings as sites for PBRs means agricultural land wouldn't be sacrificed for that purpose.

Solar radiation management by reflecting sunlight back into the atmosphere is the third idea the engineers propose for mitigating climate change's effects. This so-called albedo enhancement - albedo being the proportion of light hitting a surface that is reflected rather than absorbed - would be accomplished by replacing absorptive materials with reflective ones.

They acknowledge that their experiment-loving scientific brethren have shown that even large-scale albedo enhancement might only reduce the global surface temperature by less than a quarter of a degree. But concentrating efforts in urban areas would produce more marked results.

The "urban heat island" of central Los Angeles, for example, is typically four degrees hotter than the city's suburbs, as air is warmed by dark roofs and paved areas. Result - the air-conditioning gets cranked up, electricity demand rises and air quality suffers as the heat accelerates smog formation.

The engineers' report says tests in Florida and California suggest solar-reflective roofing can cut energy use for cooling by between 10 per cent and 60 per cent. Happily, only negligibly more heating would be required in winter.

Of the three ideas, the engineers think the best bet is establishing forests of artificial trees, because of their design simplicity, their reliance, in the main, on existing technical know-how and componentry, mass producibility and ease of dotting around the countryside.

In other words, there should be no need for scientists to get involved.

Anthony Doesburg is an Auckland technology journalist

Gas guzzlers

* "Artificial trees" would work by absorbing CO2, then storing it for disposal.
* They would be thousands of times more effective than real trees at removing CO2, says Britain's Institution of Mechanical Engineers.
* The "relatively straightforward" technology lends itself to mass production, say the engineers.
* "Trees" could be placed along motorways, where CO2 levels are high, or in remote locations near to power sources.
* The cost: Maybe US$20,000 a "tree".