A little light at the end of the global-warming tunnel

There is scientific consensus that Earth is gradually warming (although that warming is now in a bit of a lag phase) due to humanity's emissions of greenhouse gases, principally carbon dioxide. If allowed to continue, global warming will have major negative effects, including widespread coastal flooding and ecological disruption. The only hope of slowing down or reversing the warming trend is the immediate and drastic reduction of greenhouse gas emissions.

However the world is gripped by a deadly paralysis of inaction. Humanity is sleepwalking towards the edge of a deadly precipice – but now, at last, some good news. A study by Christian Azar and colleagues of Chalmers University of Technology, Sweden, published on July 10th in the journal Environmental Research Letters, demonstrates that global warming can be reversed using bioenergy with carbon capture and storage technology (Beccs).

Beccs in essence means burning trees and crops (biomass) for energy, capturing the carbon dioxide emitted in the burning process and storing it underground.

Earth warmed by 0.8 degrees during the 20th century. Current conservative estimates predict that it will warm by a further 1.1-2.9 degrees by 2100, with the highest estimates ranging from 2.4-6.4 degrees. The UN has agreed that global warming must be kept below two degrees relative to pre-industrial temperatures in order to temper negative effects.

A greater degree of warming, by no means out of the question, could have catastrophic consequences for life on Earth – some environmentalists think that we have already gone too far. The only way to slow down or reverse the warming trend is to drastically reduce greenhouse gas emissions – and we are not doing well.

The International Atomic Energy Agency recently announced that the amount of carbon dioxide emitted per unit of electricity generated barely changed from 1990 to 2010. This means that efforts to date to mitigate emissions have achieved next to nothing.

The Swedish study shows that global warming could be reversed and temperatures pushed back below the global target of two degrees above pre-industrial levels using Beccs, even if current mitigation policies fail and the target is initially exceeded. Indeed, analysis shows that the most economic implementation of Beccs would be 30-50 years from now, probably following a temporary overshoot of the two-degree target.

Near-zero emissions
The net effect of using Beccs technology, but only when combined with a reduction otherwise in emissions of carbon dioxide to near zero, would be to pump carbon dioxide out of the atmosphere because growing crops for burning in Beccs sucks carbon dioxide out of the air. Of course, the essential reduction of carbon dioxide emissions otherwise to near zero would require a massive expansion of renewable energy and/or nuclear power.

Beccs technology is a light at the end of the tunnel rather than a get-out-of-jail- free card, but the danger is that it might be interpreted as the latter, thereby excusing continuation of the current political gridlock. Azar emphasises that the potential of Beccs technology in no way relieves us of the need to urgently and drastically reduce current levels of carbon dioxide emissions. He stresses that the Beccs approach could only reverse global warming if emissions of carbon dioxide otherwise have been reduced to zero.

Even at that, Beccs could only reduce global temperatures at a rate of 0.6 degrees per 100 years, too slow to act as an “emergency brake” if accumulating climate-change damage is allowed to exceed certain modest threshold levels.

There are other caveats. Although Beccs technology has been successfully tested in small-scale trials, it remains unproven on a commercial scale. There is also a danger that a significantly warmer global climate than we have now, even for a short period, might so profoundly affect ecological and meteorological conditions that we might be unable to grow enough biomass to fuel the Beccs system.

Still, the announcement of the potential of Beccs technology is good news, as it promises a positive intervention that could rescue us from global warming. There is a paralysing fear that we may already have gone too far. We probably haven't, and the new study gives hope that if we act courageously now, things will work out – but we still lack courage.

William Reville is an emeritus professor of biochemistry and public awareness
of science officer at UCC.
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