Three Experts Reflect On: Climate Change, Cities, and the Need to Scale Up Green Infrastructure

Kevin Behan (KB) is Deputy Director with Clean Air Partnership. Kevin has an Honours Bachelor of Science from University College Dublin and post-graduate qualifications in Business Studies and Information Technology (Dublin Business School) and Spatial Analysis and GIS (McMaster University).

Dr. David R. Tilley (DT) is an Associate Professor of Environmental Science & Technology at the
University of Maryland and co-founder of a new company called which
specializes in living umbrella technology.

Dr. Brad Bass (BB) has over 20 years of experience in green infrastructure research and policy (energy, water quality, biodiversity) and climate change adaptation. He led the development the first green roof building energy model and was awarded a Lifetime Achievement Award for his contributions to green roof research in 2012.

1. What are the main issues facing North American cities with respect to climate change? 

KB: There are considerable, but separate issues facing North American cities around mitigating against, and adapting to climate change. Considering mitigation, much of the ‘low hanging fruit’ has now been picked. Many of our point source industrial greenhouse gas emissions have been regulated with controls in place. Future mitigation will rely on improvements to building energy and transportation efficiency. Fossil fuel companies continue to receive considerable subsidies to bolster their market competitiveness, so the cost of ‘going green’ is currently borne by the individual. All orders of government need to work together to create a level playing field where the negative external costs of fossil fuel energy are accounted for, increasing the attractiveness of renewables. Governments, developers and utilities need to work together to build the market for home efficiency and net zero ready homes. 

Regarding adapting to climate change, we are now at (or indeed, past) the point where the implementation of adaptation projects must happen. Adaptation projects tend to have more localized benefits. Reflecting this, municipal governments have had little or no financial or resource assistance from higher orders of government to deliver adaptation projects. The absence of a concerted effort to build resilience in our cities remains a huge stumbling block to adaptation. 

DT: The number of deadly summer heat waves that hit major cities is expected to increase in frequency and intensity as the climate warms. Excess urban heat is especially troublesome because the population of cities is growing and the mean age of city residents is increasing. The elderly tend to be more prone to suffering death and disease due to heat waves. Cities with the highest density populations and least amount of green space tend to suffer the most from heat waves. Flooding due to big storm events is also a major concern. The spread of hard surfaces for parking lots, buildings, roads and the loss of green space in cities exacerbate the damage caused by heat waves and floods.

BB: This will vary by cities. Some will deal with heat and the associated cooling costs and health impacts. Others will deal with water shortages or extreme flooding events (and associated water quality impacts). Coastal cities will need to address rising sea levels. Although I expect impacts on cities’ ecosystems, I am not sure that these will be given much attention when cities are dealing with more extreme heat or water related issues. 


2. How can increasing our use of plant based technologies (green infrastructure) in cities contribute to our ability to make them more resilient in the face of climate change impacts?  

KB: Green infrastructure is essential for both climate change mitigation and adaptation. Climate change has resulted in dramatic changes to how our rain falls. While for many North American communities, overall annual levels of precipitation are relatively unchanged, the intensity, frequency and duration with which precipitation falls has changed considerably. Green infrastructure is essential and efficient in the management of stormwater. This is especially important in the face of increasingly frequent intense rainfall events. We are also seeing increased drought periods, green infrastructure is a cost effective way to retain soil moisture during dry spells, preventing plant death and maintaining urban biodiversity. Climate change means higher temperatures in our urban areas. Through passive cooling, green infrastructure helps mitigate these temperature increases. 

DT: Plants are one the Earth’s major tools for absorbing excess heat from the Sun. Plants do this naturally by the process of transpiration, that is, the water pulled up from the soil by plants is released through small openings in their leaves. This helps plants maintain leaves at a biologically conducive temperature (as opposed to overheating). When the water is released from the leaves it goes from a liquid to a vapor, which absorbs an enormous amount of heat and energy from the Sun. Therefore, green infrastructure such as green walls, green roofs, rain gardens, and other living technologies help cool the urban environment by removing the Sun’s heat, which grey or traditional infrastructure cannot do. 

BB: Plants and green infrastructure can help mitigating the impacts of flooding (essentially by slowing down the flow and retaining water) and heat (reducing the urban heat island, through evapotranspiration and shading).

Photo provided by Serena Matt

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