Shades of green

by Philippa Nuttall Jones, Editor In Chief at FORESIGHT Climate & Energy

This article appears in REVOLVE #27
Feature 20 May 2018

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Polluted is often the first thing that comes to mind when discussing cities, but the new Treepedia tool shows that rather than fifty shades of grey, many of our cities our actually quite green.

The Treepedia online tool measures tree canopy cover in cities. Rather than count the individual number of trees, which would clearly demand significant time and resources, the creators have developed a method that analyzes the amount of green perceived while walking down a given street. This means that many green spaces are not actually included – parks for example that are not seen from street level, will not be picked up by the tool – and so your favourite city may be even brighter green than Treepedia suggests.

The tool was developed by researchers at the MIT Senseable City Lab in the United States of America, in partnership with the World Economic Forum, and uses Google Street View data to measure urban green canopies. The creators emphasize that the tool is not a gimmick and stress the importance of understanding and promoting urban tree cover due to its ability to lower urban temperatures by blocking shortwave radiation and increasing water evaporation. This will become increasingly important as climate change raises the temperatures in our cities.

Green View Index

“Increasing a city’s tree canopy contributes to lowering urban temperatures by blocking shortwave radiation and increasing water evaporation. Creating more comfortable microclimates, trees also mitigate air pollution caused by everyday urban activities. Their absorptive root systems also help avoid floods during severe rains and storm surges. So overall, trees are pretty awesome.

Cities around the world are recognizing this and many are developing strategies to increase green canopy cover. In fact, in 2015, the World Economic Forum’s (WEF) Global Agenda Council (GAC) on the Future of Cities included increasing green canopy cover on their list of top ten urban initiatives: ‘Cities will always need large infrastructure projects, but sometimes small-scale infrastructure from cycle lanes and bike sharing to the planting of trees for climate change adaptation—can also have a big impact on an urban area.’

As cities around the world race to implement green canopy strategies, we’ve developed a metric—the Green View Index—to evaluate and compare canopy cover. In collaboration with the World Economic Forum’s Global Agenda Council on the Future of Cities and the World Economic Forum’s Global Shapers community, we will continue to grow this database to span cities all over the globe. What does your green canopy look like?”

For more information:
senseable-trees@mit.edu

Currently, about 54% of the world’s population lives in cities and by 2050 the urban population is expected to grow by 2.5 billion people. As global temperatures rise gradually, extreme heat will become more common, threatening public health and local economies. To illustrate just how hot cities could become in the future, Climate Central (a U.S.-based organization of scientists and journalists researching and reporting on climate change) created an interactive tool with the World Meteorological Organization in summer 2017.

The figures are impressive.

Under a high-pollution scenario, based on current emissions trends continuing, the average land temperature worldwide is projected to rise by 4.8°C. This could mean Ottawa in Canada swopping its mild climates for the equivalent tropical climate of Belize City by 2100. Meanwhile, inhabitants in mountainous Kabul in Afghanistan could be forgiven for believing that they have been transported to coastal Colombo in India. Furthermore, due to the vagaries of geography, some cities will warm much more: Sofia (Bulgaria) for instance is estimated to suffer the greatest overall temperature shift, with temperatures rising by nearly 8.4°C by 2100 compared to today.

Increasing tree cover in cities is vital to help ensure the comfort of inhabitants and visitors and to reduce the risk of health problems.

Given the 2015 Paris climate agreement and other efforts to reduce emissions, these projections are hopefully just a bad dream. In reality though, even if we stopped polluting tomorrow, we are still locked into a certain degree of warming, with urban areas expected to suffer the most. Increasing tree cover in cities is therefore vital to help ensure the comfort of their inhabitants and visitors and to reduce the risk of health problems, and even death, particularly for older citizens, from extreme heat. During the 2003 heat wave in Europe, nearly 15,000 heat-related deaths were recorded in France, with the majority being old people stuck in boiling cities.

Trees are not just good at combatting heat, they can also mitigate air pollution and their absorptive root systems can also help avoid floods during severe rains and storm surges, highlights MIT.

About 54% of the world’s population lives in cities and by 2050 the urban population is expected to grow by 2.5 billion people.

Treepedia was launched in 10 cities, including Geneva, Tel-Aviv, and Boston; and continues to expand in municipalities across the globe. Researchers plan to make the tool more interactive in the future and give users the possibility to play an active role in helping to green their city and make it more climate change proof. According to MIT, individuals will be able to add unique tree information on an open-source street map and engage with city officials to request that new trees be planted in certain areas.

As Voltaire said, we all need to take responsibility for cultivating our garden, whether it be in our backyard or along our streets for the benefit of all.


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