Major applications of green roofs over Australia’s six major cities, with a total population of at least 13 million people, could capture more than half a million tonnes of carbon dioxide a year from city air.
These calculations are derived from a two-year study from Michigan State University, reported in early October, 2009 in the US journal “Environmental Science and Technology”.
There was no major analysis before this of likely carbon uptake of urban green roofs.
Michigan State University research determined that every square meter of green roof generally sequestered 375 grams of carbon dioxide a year.
An average Australian rooftop had an area of about 280 to 300 square metres. Well-greened. this average home rooftop area could lock up around 100 kilograms of carbon a year.
Multiply that by Australia’s 5.5 million or so urban homes, and the result (if all roofs were greened) could be a saving of around 550,000 tonnes of carbon dioxide a year via rooftop greenery in place for 20 to 50 years.
The breakthough US research was led by MSU horticulture Professor Brad Rowe and doctoral research assistant Kristin Getter. MSU maintains a comprehensive repository of green roof research.
Professor Rowe said that 375 grams per square meter was not a large amount, but that if buildings were equipped with green roofs over a large area, it would amount to a significant carbon sink for cities.
Although a roof covered entirely with vegetation was at least 10% more expensive to construct than a traditional roof, it could double roof lifespan. Increased construction costs could now be recouped within two years in the United States. In the long run, a green roof benefits the tenant, a city’s services and the environment.
Michigan R&D on rooftop carbon sequestration is a wake-up call
Green Roofs Australia Inc member, architecture Professor Janis Birkeland (pictured) of Queensland University of Technology, said the Michigan State University study was a significant wake-up call for key architecture people in Australia – where green roofs and green walls were an embryonic new built-environment industry.
Her words follow her significant 2008 authorship of the 432-page book titled Positive Development: from vicious circles to virtuous cycles through built environment design.
”Buildings can sequester carbon and produce a raft of other measurable benefits called ‘ecosystem services’. These services, such as air and water cleansing, and soil, energy, and food production, can be integrated with the urban environment”. The energy and greenhouse reductions and health benefits can pay for the costs of change ”, Professor Birkeland said.
Professor Birkeland has had a built-environment career based on sensible advocacy. She worked consecutively as artist, advocacy planner, architect, urban designer, city planner and attorney in San Francisco before entering academia in Australia.
She has authored about 100 publications on built environment and sustainability and wrote the highly-successful and widely-adopted Design for Sustainability (Earthscan, 2002). She is now Professor of Architecture at Queensland University of Technology, in Brisbane.
She said the significant Michigan study should alert Brisbane’s 400 or so architecture firms to the importance foreseen for the “Cities Alive Australia” World Green Infrastructure Congress in Brisbane in October, 2012. They also needed to alert colleagues in other Australian cities.
Brisbane’s 2012 congress was being offered $100,000 support by Brisbane City Council, and $10,000 support from Brisbane Marketing.
“But significant reduction of Brisbane people’s carbon footprints was only one of the dozen or so benefits this congress will show for green roofs and green walls plus allied technologies, she said.
Four conference themes proposed show this. They were:
- Climate Change Action Planning (already undertaken by Brisbane City Council).
- Improved urban rain-water harvesting, storage and micro-management.
- Much-advanced solar power use, using new technologies by Australian National University and CSIRO.
- Food from the roof – especially via a combination of aquaponics and vermiculture..
Improved architectural design was the key link. “Poor architecture and urban design kills more people every year than terrorism” Professor Birkeland said.
“Apart from exacerbating the effects of floods, droughts, storms, earthquakes and waterborne diseases, urban development often causes city temperatures to rise by two degrees Celsius or more.
“This urban heat island effect has killed thousands of people during heat waves in many cities around the world, the most recent of which was 3,000 one hot day in Paris in 2003,” she said.
Yet, one of the easiest urban cooling solutions was green roofs and walls designed into buildings, which could pay for themselves in a few years through energy savings, Professor Birkeland said.
To be ‘sustainable’, a built environment would need to leave Brisbane’s ecology, as well as its people, better off after construction than before. Restoration or remediation is not enough because we have already exceeded the Earth’s ecological carrying capacity,” Professor Birkeland said.
The only way we can support even existing bio-regions and populations sustainably is to retrofit urban areas to increase the net ecological carrying capacity of cities.
Buildings must not only produce clean energy, water, soil, air, and food, but must also reverse the impacts of previous development and expand ecosystems in absolute terms. The best way to start was with green roofs and green walls technology about to be specially developed for Brisbane by Queensland universities, she said.
“We cannot improve upon nature, so the only way we can increase the Earth’s ecological carrying capacity is to retrofit citiesto generate natural, as well as social, capital.
This could be done in Brisbane by providing good infrastructure for ecosystem services and bio-productive functions, such as green roofs and living walls.
We can easily modify our urban environments to create the infrastructure, conditions and space for increasing the ‘ecological base’ (ecosystem goods and services, natural capital, biodiversity and habitats, ecological health and resilience) and the ‘public estate’, or universal access to the means of survival and bio-security.
“Green roofs and green walls for Australia’s hot, dry conditions can contribute to both”, she said.
Professor Birkeland said current means of assessing building quality is based on a meaningless standard, which was less harm than ‘typical buildings of the same kind’.
“Today we have the capacity to determine the pre-settlement ecological conditions. A sustainability standard would measure improvements over the original extent and level of ecosystem health, productivity and services. At QUT, we are working on measuring the value of ecosystem services in the built environment,” she said.
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