In our all-too-hectic urban lives, a city park is a great place to unwind. Trees and green spaces have mental health and well-being benefits, on top of being great for relaxation and recreation.
Trees also help reduce air pollution. According to the study Tree and forest effects on air quality and human health in the United States, particulate matter, which is particularly damaging to lungs, is retained on tree surfaces, while leaves act as filters, absorbing polluting gases.
But the study also warns that while trees can mitigate the effect of air pollution, deposits of air pollutants on leaves can also affect photosynthesis “and therefore potentially affect pollution removal by trees”. As with everything, balance is key.
The cooling effect of trees
Trees can also significantly cool temperatures in cities. In hot climates, tree cover can reduce energy expenditure on air conditioning, while driving down the consumption of air polluting fossil fuels that power these cooling systems. Experimental investigations and modelling studies in the United States have shown that shade from trees can reduce the air conditioning costs of detached houses by 20–30 per cent.
“Trees could reduce temperatures in cities up to 8°C, lowering use of air conditioning and related emissions by up to 40 per cent,” says Simone Borelli, an Agroforestry and Urban/Periurban Forestry Officer with the Food and Agriculture Organization of the United Nations.
“When part of a wider landscape mosaic, large green patches within and around cities would also reduce emissions through avoided sprawl and excess mobility requirements,” he adds.
Urban tree-planting has to be done right. Species planted should be ones that are most effective at trapping pollution, typically those with large leaves. Officials also need to account for things like wind patterns and tree spacing. If water is scarce, they’ll want to consider drought-tolerant varieties, and avoid trees that increase pollen and allergies.
Action is all the more important given that urbanization is accelerating—the proportion of people living in cities will be 60 per cent in 2030 and 66 per cent in 2050. Nearly 90 per cent of this increase will occur in Africa and Asia. To address the impacts of this rapid growth and the related challenges, a large-scale effort is needed.
Building the Great Green Wall of Cities
Nearly 8,000 km long and 15 km wide, the Great Green Wall is an African-led movement of epic proportions initiated in 2007 to green the entire width of northern Africa, a semi-arid region extending from Senegal to Djibouti. A decade in and roughly 15 per cent under way, the initiative is slowly bringing life back to some of Africa’s degraded landscapes, providing food security, jobs and a reason to stay for the millions who live along its path.
An initiative of this nature in urban areas is being developed by the Food and Agriculture Organization and other partners in preparation for the UN Climate Summit in September 2019. It aims to create up to 500,000 hectares of new urban forests and restore or maintain up to 300,000 ha of existing natural forests in and around 90 cities of the Sahel and Central Asia by 2030. Once established, this “Great Green Wall of Cities” would capture 0.5–5 gigatonnes of carbon dioxide per year and stock carbon for centuries.
On 1 March 2019 the UN General Assembly established the UN Decade on Ecosystem Restoration 2021-2030, which should give further impetus to tree-planting efforts.
“UN Environment promotes the planting of trees as a key way to mitigate climate change and boost land-based biodiversity, 80 per cent of which is in forests,” says Tim Christophersen, head of UN Environment’s Freshwater, Land and Climate Branch, and Chair of the Global Partnership on Forest and Landscape Restoration. “We are working with partners across the planet to boost tree planting for ecosystem restoration. There is scope for planting one trillion more trees, in addition to the 3 trillion that already exist on Earth. But it has to be done right; planting indigenous trees, supported by local communities, is a good way to go.”
Let the stones gather some moss
In those forest ecosystems, trees are not alone in cleaning the air. An ambitious project by Greencity Solutions in Berlin, Germany, seeks to marry high-tech applications with another natural air purifier: moss.
“The ability of certain moss cultures to filter pollutants such as particulate matter and nitrogen oxides from the air makes them ideal natural air purifiers,” says Greencity Solutions.
“But in cities, where air purification is a great challenge, mosses are barely able to survive due to their need for water and shade. This problem can be solved by connecting different mosses with fully automated water and nutrient provision based on unique Internet of things technology,” it explains.
Or by planting more trees that will provide the cover and humidity, that will help moss take hold and grow.
Global housing crisis: Urgent action needed on planning, policy and technology
The world must act now to address the crisis in affordable housing. According to a new report by the World Economic Forum, Making Affordable Housing a Reality in Cities, about 90% of cities around the world do not provide affordable housing or of adequate quality. The report says that the cost of housing, as well as location, prohibits people from meeting other basic living costs, threatening their employment and fundamental human rights.
In Africa, more than half of the population live in sub-standard conditions, and in India and China, almost a quarter of the population live in informal settlements. Across the world, millennials spend more on housing than previous generations and have a lower quality of life. By 2050, more than 30% of the urban population around the world, about 2.5 billion people, will live in sub-standard housing or be financially stretched by housing costs.
“A world in which only a few can afford housing is not sustainable,” said Alice Charles, Lead, Cities, Urban Development and Urban Services, World Economic Forum. “If cities are to find solutions, it requires a broader understanding of what constitutes affordability and the factors that affect it. This report explores both supply-side and demand-side dynamics affecting affordability and guides decision-makers towards strategic interventions and long-term reforms that can reduce dependence on government support systems and incentivize more commercially viable affordable housing through policies and practices that address systemic gaps in the housing value chain.”
The key challenges to affordable housing include land acquisitions, zoning and regulations that affect land use, funding mechanisms, and design and construction costs. Examples of innovative approaches to support affordable housing include:
· The cities of Chengdu and Chongqing, China, are making land available through tradable land quotas, allowing agricultural land to be converted to urban use.
· The Communities Plus Programme in Sydney, Australia, is partnering with the private sector to develop 23,000 new and replacement social housing units, linking housing assistance with participation in education, training and local employment opportunities.
· Hamburg, Germany, and Copenhagen, Denmark, are pooling publicly owned assets into an Urban Wealth Fund that works with the private sector on affordable housing development projects.
· Employers such as Facebook and Google in the US, IKEA in Reykjavik, Iceland, Lego in Billund, Denmark, Samsung in Seoul and Suwon, Republic of Korea, and Alibaba in Hangzhou, China, are investing in housing developments for employees.
· London, UK, is offering construction training to address the skills shortage in the industry.
· Mexico is deploying bricklayer robots that increase construction productivity.
· Austin, US, Beijing and Shanghai, China, and Eindhoven, Netherlands, are exploring 3D printing to build homes.
· Denver, US, is mandating certain buildings to install green roofs or solar panels to save on energy costs for the occupants.
· Dupnitsa, Bulgaria, and Poznan, Poland, are changing eligibility criteria for social housing projects to support more citizens.
· Bristol, UK, is constructing homes with six types of housing tenure, including build-to-rent, shared ownership and rent-to-buy models.
· MIT’s Media Lab has developed an 18.5 square-metre prototype apartment that uses transformable furniture that can be flipped, moved and stowed by hand gestures and voice commands, increasing the functionality to an apartment three times its size.
The report also outlines recommendations for city governments, the private sector and non-profits, including:
· City governments must develop regulations that emphasize property rights, protect tenants, support mixed-income housing development and enable innovative financing models.
· The private sector should work with local communities to provide affordable housing for employees, support new financing mechanisms and help meet housing costs. Private developers must invest in sustainable, energy-efficient design and use new materials, equipment and technologies to increase productivity.
· The non-profit sector should work with cities and private developers to offer alternative tenure models, provide policy development and technical support, and educate and advocate for citizens.
Ensuring affordable housing is critical to achieving the United Nations Sustainable Development Goal 11, which aims to make cities inclusive, safe, resilient and sustainable. According to the 2016 New Urban Agenda, housing policies can affect health, employment, poverty, mobility and energy consumption.
Making Affordable Housing a Reality in Cities was created in collaboration with PwC.
A new green chapter for China’s fabled lakeside city
Hangzhou has seen its share of history. A millennium ago, the city was the seat of two separate dynasties for over 200 years, putting it in storied company with China’s six other ancient capitals. In 1972, during his “week that changed the world”, Richard Nixon strolled the shores of the city’s West Lake with Chinese Premier Zhou Enlai. Their discussions by the water spurred China’s historic economic opening.
Forty-four years later, another meeting between Chinese and American leaders in Hangzhou marked a profound global change. It was here that President Xi Jinping and President Obama announced that both of their countries had ratified the Paris Agreement on climate change.
These days, Hangzhou is not content to be a mere witness to history. Instead, the city is writing its own story using broad green strokes.
Hangzhou is rapidly modernizing its public transit network. In 2008, it was Hangzhou that launched China’s first bike sharing system, which is now the world’s largest.
Its bus network is becoming greener as well. Seventy per cent of public buses in the city are now electric. It’s no small investment. Each bus costs US$145,000, which is about double the price of a conventional public bus.
But the outlay is well worth it, according to Vice Mayor Hu Wei. “The most important thing is that we can protect the environment and fight air pollution,” he says.
Even though the initial cost is high, over the lifetime of the bus the cost is the same or less compared to a conventional equivalent. And they are getting cheaper. Since the buses were introduced in 2014, operating costs have dropped by between 30–40 per cent.
“The challenge is to convince other businesses like tour companies to use these greener buses,” says the mayor.
The subway network is expanding as well. It already covers some 170 kilometres, but the city is building new lines that will bring it closer to 500. While the metro is currently more expensive than the bus, the expansion will allow the government to bring costs down for commuters.
In the face of persistent air pollution, investments are not the only tool at the government’s disposal. The government is also taking hard decisions. In 2015, a 59-year-old steel plant was shut down to improve air quality. The government estimates the closure will prevent 3,000 tonnes of soot from entering the skies in the city.
Speaking at World Environment Day celebrations in Hangzhou, Che Jun, the Party Secretary of Hangzhou’s home province of Zhejiang, painted a bleak picture of the area where the plant was located. “Air was permeated with a pungent smell. All of the rivers in the areas were strangers to fish and shrimp. All of Hangzhou was a victim,” he said.
Concerns over the economic impact of the shutdown were short-lived. The company “leveraged the tailwind of the digital economy… and was reborn” said Che. “In 2018, their profit hit CNY3.53 billion [US$511 million].”
The former home of the steel plant is now part of the 65 per cent tree cover that Hangzhou enjoys. This has heralded a natural revival. “This spring we saw tens of thousands of egrets coming to the city,” said Che. “Now, egrets flying against the setting sun has become an iconic image of the city this year.”
Hangzhou’s green rejuvenation may be nowhere more in evidence than Xixi National Wetland Park, a 2,800-acre integrated urban, agricultural and cultural wetland in the west of the city. Though the wetland has been a natural part of the landscape for almost 2,000 years, the government pushed for its revival in 2005. The park has come back to life, with the number of bird species seen in the park has increased from 79 before the rejuvenation to 181 today. And it’s a functional revival as well. As water circulates between Xixi, the Qiantang River and the UNESCO-listed Grand Canal, the wetland acts as a natural kidney, filtering pollutants from the water.
More than 700 years ago, the Venetian explorer Marco Polo said that while heaven may contain paradise, Earth had Suzhou and Hangzhou.
Today, city officials in Hangzhou are doing everything they can to maintain their claim to this earthbound eden.
Four Things You Should Know About Climate-Smart Cities
Singapore, host of this year’s Innovate4Climate (I4C) conference, is one of the world’s leading cities for climate-smart urban development. In the lead-up to this year’s I4C event, here are four elements of climate-smart urban development worth knowing.
First, cities can play an important role in climate-smart development
Today, 55 percent of the global population lives in urban areas. This figure is forecast to increase to 68 percent by 2050 – adding 2.5 billion additional people to cities. Over the next 35 years, more than 1.2 billion people in all, or one-third of the world’s urban population, are expected to live in Asian cities alone.
Cities across the world are major contributors to global emissions. Today, it is estimated that cities account for more than 70% of all global CO2 emissions each year – more than 25 billion tons. This is the equivalent of more than 5 billion cars on the road. As these cities grow, so too will their carbon footprint, in the absence of concrete action to help improve urban development. Moreover, as cities develop, their exposure to climate and disaster risk also increases. Almost half a billion urban residents live in coastal areas, increasing their vulnerability to storm surges and sea level rise. Many of Asia’s megacities – Bangkok, Dhaka, Guangzhou, Ho Chi Minh City, Kolkata, Manila, Mumbai, Shanghai, Yangon – are low-lying or coastal cities and highly vulnerable to rising sea levels, floods, and other impacts of climate change: while all coastal cities will be affected by sea-level rises, Asian cities will be particularly badly affected. About four out of every five people impacted by sea-level rise by 2050 will live in East or South East Asia.
Building cities that “work” – inclusive, safe, resilient, and sustainable – requires intensive policy coordination and investment choices. Once a city is built, its physical form and land use patterns can be locked in for generations, leading to unsustainable sprawl. Many cities are already at the forefront of innovative climate solutions, ranging from policies to reduce emissions through transit-oriented development and energy efficiency efforts to building more resilient urban infrastructure that can better withstand the impacts a changing climate.
Second, the populations and emissions of Asian cities are growing fast
Asia’s cities already consume 80% of the region’s energy and create 75% of its carbon emissions. Asian cities are poised to contribute more than half the rise in global emissions over the next 20 years if no action is taken.
India and China, for instance, are two of the three countries that will account for 35 percent of the world’s projected urban population growth by 2050. Without action, this rapid growth will also lead to increasing emissions.
Third, Asian cities can also play a significant role in combating climate change
While high pollution levels of Asian cities tend to capture global attention, many cities in the region are also at the forefront of climate-smart policies, innovations, and investment. Emerging market cities in Asia and around the world have the opportunity to leapfrog historic approaches to urban development, instead putting in place resilient, green infrastructure for coming generations. A recent report by IFC on Climate Investment Opportunities in Cities estimated that emerging market cities have the potential to attract more than $29.4 trillion in cumulative climate-related investments in six key sectors by 2030, including climate investment opportunities in Asia of some $20 trillion.
For instance, by 2020, Beijing plans to replace over 70,000 gasoline and diesel taxis with electric vehicles. Seoul is aiming to add 2000 km of bike paths and create 250 pedestrian zones. Hanoi plans to generate electricity from its biggest landfill, which will reduce emissions and generate electricity.
Fourth, Singapore, host of I4C, excels at climate-smart urban development
With nearly 8,000 people per square kilometer, Singapore has the world’s third highest population density. Singapore is a prime example of how innovation, technology, and strategic urban development can meet urban development and climate demands. In addition to hosting the world’s largest underground district cooling network in the world, the country is also home to the Semakau landfill: an offshore landfill and a model for climate-smart development. The landfill deploys an innovative waste disposal design, comprising silt screens to protect the surrounding coral and an impermeable layer to deter leaching, ensuring that the man-made island remains habitable for a diverse range of marine life. An onsite waste-water treatment plant also ensures that excess water is treated before being discharged into the surrounding sea. The site is so clean and efficient that it is a popular tourist attraction!
An additional way the country is utilizing the surrounding sea as it develops is the introduction of the country’s largest offshore floating solar panel system, expected to go online later in 2019. This five-hectare facility is expected to generate more than 6,000 megawatts of power and will help to reduce more than 2,000 tons of greenhouse gas emissions every year – while not occupying a single centimeter of precious land, a scarce resource for the tiny nation.
I4C looks forward to learning from Singapore and sharing their climate-smart experiences with the world.
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