Covering rooftops with plants can act to strip the atmosphere of CO2 to some extent, according to a new report carried out by Michigan State University and published by Environmental Science and Technology.  The scientists behind the report stressed that rooftops gardens should not be considered a climate change solution in their own right, but that they can still be a useful carbon capture tool. 

“The key to fighting global warming is capturing carbon from the atmosphere and storing it in new reservoirs that weren't storing carbon before”, head scientist Kristin Getter explained.  “In the whole scheme of things, green roofs are not the one answer to sequestering carbon, but they will certainly help.”

Before now, green roofs were already known to have a positive effect on the environment.  Their heat absorption and reflection abilities act to reduce the need for summer air conditioning while, in the colder months, they provide an additional layer of insulation.  In an urban context, green roofs can lower noise and air pollution levels too and – just as with large forest areas – they act as carbon sinks, albeit on a reduced scale.

Capturing Atmospheric CO2

No previous study had been carried out before this one that had quantified the process of capturing atmospheric CO2 where a typical green-roofed home was concerned.  According to the scientists’ calculations, though, the average carbon concentration for every square metre of green roof examined was 375 grams.  To put this in context, said the scientists, the city of Detroit has up to 85 million square metres of roof: planting over all of this would remove an amount of atmospheric CO2 equivalent to the emissions produced by 10,000 trucks over a 12 month period. 

One point, though, is that green roofs won’t go on removing CO2 from the atmosphere indefinitely.  At some point down the line – said Portland State University engineer David Sailor – typically after two years, the level of carbon being emitted will neutralise the impact of the carbon being taken in.

“Their [the Michigan scientists’] argument is that the carbon sequestration in plant biomass should be considered one of the co-benefitsof a green roof”, he stated.  “Taken along with other co-benefits, you start to tell a very compelling story for green roofs.”

See also:

Artificial Forests to Capture CO2