Guelph – New research reveals that many of today’s urban design solutions meant to keep cities cool will do little to stop temperatures from rising at night unless they are accompanied by substantive reductions in greenhouse gas emissions.

Urban expansion and greenhouse gas emissions are fuelling climate change, with temperatures in American cities expected to rise by 2 to 7 degrees Celsius by the year 2099. To gain a deeper understanding of what might be in store for cities in the future, researchers around the world are using modelling and computer simulations that explore the dynamics of climate change and urban sprawl.

Now, a team of researchers from the University of Guelph in Ontario, Canada, and Arizona State University have completed some of the most sophisticated modelling of the effects of climate change and urban centres in the US, with a particular focus on heat-mitigating technologies such as cool roofs, green roofs and street trees.

“Using dynamically interactive simulations, we examined multiple adaptation strategies with the aim to offset projected 21st-century urban heat,” co-author E. Scott Krayenhoff of the University of Guelph, said in a statement. “We combined high intensity implementation of cool roofs, green roofs and street trees (i.e. a full adaptation scenario) and found that it leads to 1.3 to 2.0 C of summertime mean afternoon cooling depending on the region but less than 1 C night-time cooling.”

Even with these heat-mitigating technologies, the computer simulations showed that the heat is likely to persist under both the business-as-usual scenario as well as scenarios where greenhouse gas emissions peak by 2040. “This means that we can build ‘cool’ buildings and plant trees in our streets and still US cities are likely to become a lot hotter without concurrent and substantive greenhouse gas emissions reductions,” added Krayenhoff.