One of the most important convenient truths and responses to the problem is literally over our heads: the greening of our roofs to help counter climate change effects. The world’s rapid urbanisation has meant that the “heat island effects” of cities are significant contributors to measured global warming. Compared with nearby rural areas, a city’s ambient temperature can be six to 10 degrees Celsius warmer because of heat absorbed and then released from roadways and buildings. Green roofs reduce ambient temperatures in cities. Plants help trap carbon dioxide, nitrous oxide, ozone and PM10 particulates and sulphur dioxide levels – which together cause additional heat island effects as well as unhealthy urban pollution.
The idea that greenery can be on the roofsof homes and city buildings has been around for many years, but in Australia it has seldom been acted upon. European countries such as Germany, Austria and the Netherlands have already developed green roof technology and regulations to a high level of cost-efficiency and positive environmental impact. North American municipal governments are also showing substantial financial and environmental benefits from well-engineered rooftop gardens costing around US$14 a square foot (approx A$100 a square metre).
A 2005 study by Canada’s Ryerson University showed that an 8% cover of green roofs over a city (Toronto) reduced the city’s heat island effect by up to two degrees Celsius. The Ryerson study also revealed the following green roof technology benefits:
- direct energy savings of Can$12 million a year in buildings from reduced cooling demand in summer.
- indirect city-savings at peak load demand of Can$80 million a year.
- slower runoff of rainfall at peak times – meaning cost savings of Can$79 million a year from reduced capital costs for storm-water management, erosion control and sewer overflows.
The City of Toronto has consequently encouraged its built-environment industry to design and implement green roofs, and to explore green roof retrofits. Brisbane City Council has told me it will do the same.
An ideal plant gene pool
This is great news for urban planners, as green roofs offer considerable potential to the Australian economy. Key to the technology’s benefits is the greenery itself. Our extraordinarily diverse and weather-hardy plant gene pool is ideally placed to help slow down climate change effects. Already the northern hemisphere advance guard has begun seeking out Australian native plants for its rooftops. Why should we wait for these countries to swipe our best?
Australia has myriad business and export opportunities in cultivating our native plants with a capacity to range from plants sourced from Tasmania and Victoria’s relatively cooler climates, to the dry arid zones of South Australia and Western Australia, to the tropics of Queensland and the Northern Territory.
Australian native vegetation is low-maintenance and visually attractive. Native flowering plants can support horticultural and roofscaping businesses, while providing restful retreats across CBDs and sun-dried suburbia. Biggest payoffs are reduced fossil fuel energy use, and more efficient water use – two points that should resonate across municipal, state and federal government levels.
Growing vegetables and fruit on urban rooftops is a huge fresh food business opportunity for many, utilising roof-compatible technologies such as hydroponics, aquaculture and aquaponics. Other potential economic spin-offs include extra revenues for building owners renting for food from the roof, not to mention a vastly improved office or work environment for tenants. Real estate valuers are similarly predicting that retrofitted green roofed buildings will improve in value by at least 5% to 10%.
What a great, “win-win” way to respond to the issue of climate change!