Engineers call for 'artificial trees' to reduce CO₂

Most attempts to deal with climate change involve reducing emissions of CO₂ and in December the United Nations Convention on Climate Change in Copenhagen will attempt to set binding targets for lowering such emissions for the first time. Yet even an agreement to cut CO₂ emission by 50% by 2050 might not be enough to stop the planet's average temperature rising by 2°C by the end of the century.

Geoengineering – deliberate intervention into the climate system to counteract man-made global warming – offers an alternative approach. The new report, Geoengineering – Giving us Time to Act?, looks at different geoengineering options for tackling climate change, including adding iron to the oceans to produce phytoplankton blooms that then absorb CO₂ and to construct giant sunshades in space that can reflect the Sun's rays.

Absorbing carbon
The authors – led by Tim Fox, head of environment and climate change at the Institution of Mechanical Engineers – found that constructing fly-swat-shaped "artificial trees" is the most promising approach to reduce CO₂. Such a tree would work by letting air pass through into the structure and then catching the CO₂ via a "sorbant" material, such as sodium hydroxide. The CO₂ is then removed and buried underground in a similar manner to conventional carbon capture and storage.

According to the report, constructing 100,000 such "trees" – each costing around $20,000 – would require 600 hectares of land but would be enough to remove the CO₂ from the UK's homes and transport system.

Algae to the rescue
The report also recommends coating buildings with algae, which would absorb CO₂ via photosynthesis. The authors state that the algae can then be "periodically harvested from building surfaces and used as biofuel".

The third recommendation is to make building surfaces more reflective. Although the authors claim that this method may not be as effective as the other two, "it does have the additional benefit of reducing temperatures in city centres, [which] can often be several degrees hotter than the surrounding environment".

The report also outlines a 100-year roadmap for geoengineering in the UK, which calls for £10m a year in funding to help bring together climate scientists, economists and engineers as well as the development and deployment of "smart grids" to manage demand by communicating with electricity meters in homes.

A separate report on geoengineering by the Royal Society is due to be published on Wednesday.