As scientists predict that global warming could surpass the critical 2°C threshold within the next few decades, engineers have started to consider "geo-engineering" as a short-term strategy to buy time to put in place low-carbon strategies.
It essentially encompasses technologies that try to cool the planet either by reflecting some sunlight back into space or by removing CO2 from the atmosphere.
A new report from the Institution of Mechanical Engineers looked at hundreds of options, concluding that three of them were practical.
Artificial trees could be planted to soak up CO2 several thousand times more effectively than normal trees, the engineers say. The trees would capture the greenhouse gas from the air to a filter medium, where it would be collected and stored underground as is the case for carbon capture and storage technology developed for power plants (CCS; see EurActiv LinksDossier).
With current technology, a tree the size of a shipping container could absorb CO2 emissions equivalent to those of 20 US cars, the team said. However, technological advances would enable a single collector to absorb ten times more CO2, they forecast.
"Artificial trees are already at the prototype stage and are very advanced in their design in terms of their automation and in the components that would be used," Dr. Tim Fox, the lead author of the study, told BBC News. He added that they could be mass produced in a relatively short time.
The team's other preferred method to capture carbon is using photosythesis in algae. Strips of algae could be fitted to the outside of buildings and then used as biofuel (see EurActiv LinksDossier on 'Algae: The ultimate biofuel?').
The final option floated in the report is to reduce incoming solar radiation by reflecting it back from building surfaces. This could best be done by installing solar-reflective rooftops, it concludes.
The institution would like to see geoengineering included in wider global climate mitigation and adaptation plans, supporting decarbonisation efforts. It calls for government funding for geo-engineering research, while stressing that this must be linked to existing research into climate mitigation and adaptation.
New arms race?
Sceptics criticise geo-engineering solutions for failing to tackle the cause of the problem: CO2 emissions from burning fossil fuels. In order to effectively cut greenhouse gases, concerted efforts from all major polluting countries are required, but agreement is proving difficult to reach.
The Kyoto Protocol intended to slash emissions in industrialised countries by only 5.2% below 1990 levels by 2012 and suffered a major setback when the US did not ratify it. Negotiations to agree a successor to the treaty in December have so far offered little evidence that developed countries will be ready to commit to the 25-40% reductions required by 2020 to set the pace for a sustainable future.
Geo-engineering, on the other hand, could potentially be a strategy that any advanced economy can pursue unilaterally from their own territory. Concerns abound that this could open the door to a modern arms race, as countries rush to set up research programmes in order to deploy different technologies in the most beneficial manner.
"Norms to govern deployment of geoengineering systems will be needed soon," said David Victor, a professor at Stanford Law School. Writing jointly with a number of prominent researchers in 'Foreign Affairs' magazine in April, he argued that geo-engineering is essentially a political choice, as one option will benefit some countries by easing the impact of climate change, while others might find the risks larger.
The researchers point out that altering the earth's reflectivity, known as albedo, could alter rain patterns, impacting seriously on freshwater supply and agriculture in areas vulnerable to drought. At the same time, other areas would experience the benefits of planetary cooling, such as less frequent extreme weather conditions, for example.
Critics of experimenting with climate engineering stress that it is impossible to anticipate the impact of toying with the climate system.
"Geo-engineering is the very last resort that should not be contemplated before we have even seriously tried to reduce emissions. There are many serious risks associated with the various geoengineering options, and they assume that we understand the climate system well enough to tinker with its components," Professor Stefan Rahmstorf from the Potsdam Institute for Climate Impact Research told EurActiv.
Moreover, if factories around the world are allowed to continue to spew out emissions at an increasing rate, cooling the planet artificially will not stop the build-up of CO2, acidifying oceans, experts say.
"The one thing we do understand very well is that CO2 emissions cause warming, and we need to tackle the root cause of the problem by reducing these emissions. Everything else would be foolhardy," Rahmstorf concluded.