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.
Cities: Where the fight for a green recovery will be won or lost
Cities are home to 55 per cent of the world’s population, all jammed together cheek-by-jowl. Little wonder, then, that cities are being hit hardest by COVID-19: an estimated 90 per cent of all reported cases have occurred in urban areas.
But the same concentration of people also makes cities the places where the battle for a green recovery from COVID-19 – which is essential to reduce future pandemic risks and fight climate change – can be won.
Cities are breeding grounds for ideas and the places where many new techniques to reduce climate change, pollution, resource use and biodiversity loss are taking shape. Before COVID-19, many cities had already adopted urban farming, e-mobility, non-motorized transport, and were exploring zero emission buildings, district energy and decentralized renewable energy systems, nature-based solutions, and retrofitting projects.
The trillions of dollars likely to be invested in COVID-19 recovery packages can accelerate such developments.
“As we respond to the pandemic and work towards recovery, we look to our cities as hubs of community, human innovation and ingenuity,” said UN Secretary-General António Guterres at the recent launch of a policy brief on COVID-19 in an urban space. “Now is the time to … recover better, by building more resilient, inclusive and sustainable cities.”
Future proofing economies
COVID-19 recovery provides an opportunity to future-proof economies: for cities to clear their air, green their open spaces, and embrace solutions that help decarbonize and drive down resource use and related impacts on ecosystems, while creating new jobs.
Urban planning and design that helps create strategically dense cities and connects housing with transport and energy planning, as well as grey with blue and green infrastructure to harness benefits from nature-based solutions, will be critical.
UNEP is also working with ICLEI, through its Cities Biodiversity Center, to support multi-level governance for people and nature to live in harmony in and around our cities.
“We must pursue a green, resilient and inclusive economic recovery,” said Guterres. “By focusing on high ecological transformation and job creation, stimulus packages can steer growth towards a low-carbon, resilient pathway and advance the Sustainable Development Goals.”
Climate change: the next threat
The need for such action is urgent. COVID-19 may be currently taking centre stage, but climate change is still waiting in the wings.
Coastal cities are already enduring devastating floods, coastal erosion, sea-level rise and extreme weather events linked to climate change. Cities also suffer higher temperature than non-urban areas. Today, around 200 million city-dwellers in over 350 cities live with summer temperature highs of over 35°C (95°F). The number of cities chronically affected by heat-stress is predicted to rise to 970 by 2050. All these factors pose serious threats to people’s health and livelihoods, and our economies overall.
While cities are vulnerable to climate change, some 75 per cent of global carbon dioxide emissions are from cities. This means that the key to a decarbonized transition is held by the mayor and city councilors. Over 70 large cities, representing 425 million people, have committed to carbon neutrality by 2050. This is a start: 227 cities annually produce more than 10 million tonnes of carbon dioxide. We need a five-fold decrease in emissions to limit temperature rise to 1.5°C.
Success is possible. Cities have a long tradition of reinventing themselves, not least in response to previous pandemics that brought the introduction of sewage systems, public parks and housing regulation to improve sanitation and reduce overcrowding.
Connecting nature, climate and land use
Bangkok’s Chulalongkorn University Centenary Park is a perfect example of nature-based strategies at the crossroad of health, urban resilience and climate goals. The park’s innovative design reduces flooding risk by absorbing and storing water, which is then used for irrigation in the dry season.
Medellin in Colombia, meanwhile, has embraced nature as a cooling solution through its ‘Green Corridors’ project, transforming 18 roads and 12 waterways into lush, green havens of cool shade. The project has reduced the surface temperature in Medellin by 2-3 ̊C while improving air quality and biodiversity.
Multi-level governance crucial
Cities and nations are increasingly working together on socio-economic recovery through multi-level governance on decision-making. Ministers and mayors recently came together to accelerate climate action in an event organized by UNEP, the United Nations Development Programme, UN-Habitat, the Global Covenant of Mayors, ICLEI and United Cities and Local Governments (UCLG).
Over 300 participants – including ministers from Italy, Indonesia, Ivory Coast, Ethiopia, South Africa, Chile, and over 25 mayors and governors – discussed coordination on climate change, particularly in key sectors such as buildings, transport, agriculture and waste management.
Green strings for stimulus packages
As all levels of government plan for socio-economic recovery, stimulus packages could support cities’ transition to decarbonization. Urban investment can promote compact, integrated, mixed-use cities that reduce the distance between place of work and place of residence. The regeneration of green spaces, rethinking urban mobility and promoting public and non-motorized transport, investing in retrofitting buildings to reduce inequalities will help improve well-being and create more jobs.
“Cities are on the frontline of impact, but also of the solutions,” said Andersen. “Greening cities has health benefits, helps climate mitigation and adaptation and creates jobs.”
Coronavirus: Reshape the urban world to aid ‘ground zero’ pandemic cities
Cities have proved to be “ground zero” the world over for the COVID-19 pandemic, the UN chief said on Tuesday, encouraging leaders everywhere to “rethink and reshape the urban world” as we recover.
“Now is the moment to adapt to the reality of this and future pandemics”, Secretary-General António Guterres said in his recorded message launching the latest UN policy brief, “COVID-19 in an urban world”.
“And now is our chance to recover better, by building more resilient, inclusive and sustainable cities”, he added.
Even the scales
Mr. Guterres highlighted deeply rooted inequalities in the poorest areas, citing strained health systems, inadequate water and other challenges that cities are facing in common, with 90 per cent of reported coronavirus cases concentrated in urban areas.
However, the report reveals that urban density does not inevitably correlate with higher virus transmission, saying that vulnerabilities are largely a result of the choices made on how people live, work and travel, in and around them.
Hubs of resilience
But cities are also home to extraordinary solidarity and resilience.
Pointing to the numerous examples of strangers helping each other, streets filling with citizens showing their support for essential workers, and local businesses donating life-saving supplies, Mr. Guterres maintained that “we have seen the best of the human spirit on display”.
“As we respond to the pandemic and work towards recovery, we look to our cities as hubs of community, human innovation and ingenuity”, the top UN official said.
The UN released the guidance to reflect upon and reset how we live, interact and rebuild our cities.
In responding to the pandemic, the first line of business is to tackle inequalities and safeguard social cohesion, said Mr. Guterres.
“We must prioritize those who are the most vulnerable in our cities, including guaranteeing safe shelter for all and emergency housing to those without homes.”
Noting that nearly one-quarter of the world’s urban population lives in slums, he flagged that public services in many cities require “urgent attention”, particularly in informal settlements.
Since access to water and sanitation are vital, Mr. Guterres mentioned how some local governments have stepped up, “from prohibiting evictions during the crisis, to putting in place new clean water stations in the most vulnerable areas”.
Bolster local government
To support and strengthen local governments, the world’s top diplomat underscored the importance of deeper cooperation between local and national authorities.
“Stimulus packages and other relief should support tailored responses and boost local government capacity”, he said.
Steering the future
Another key policy recommendation is for cities to pursue a green, resilient and inclusive economic recovery.
Against the backdrop of new bike lanes and pedestrian zones to improve mobility, safety and air quality in cities, Mr. Guterres said that “we must act with the same urgency”.
He observed that by embracing widescale telecommuting away from offices, it showed that “societies can transform seemingly overnight to confront urgent threats”.
Mapping the juxtaposition of sustainable-affordable housing in the post Covid world
The pandemic has definitely taken a vice grip of the entire world’s institutional paraphernalia which has severely affected not only the public health mechanisms but also economies across the globe. However, the present piece shall be hovering over an offshoot of this pandemic which has been incessantly ignored by the world at large. The problem in question shall pertain to the issues of affordability as well as sustainability when it comes to housing. Sustainability has been echoed in various international instruments starting from Stockholm Declaration of 1972 to Montreal Protocol in 1987 to Earth Summit in the year 1992. But the Millennium Development Goals and Sustainable Development Goals have put the sustainability debate at the forefront in the international legal regime. But, the inter-relationship of sustainability with the housing mechanism has not been explicitly recognised under the international legal regime. There have been passing references pertaining to clean water and sanitation, putting efforts for affordable and clean energy and making of sustainable cities and communities that have been provided in the Sustainable Development goals laid down in the year, 2015. The goals are absolutely silent on the issue of affordable-sustainable housing. However, United Nations Organization has been pragmatic in adopting the Geneva UN Charter on Sustainable Housing in the year 2015 which is the first as well as the fundamental international convention on the issue in question. This international convention explicitly talks about the goal of achieving the sustainable housing system and also lays down the challenges emanating out of the same.
Sustainability- A term difficult to decipher
However, the term “sustainable” housing is difficult to comprehend completely. There cannot be a straight jacket solution in deducing its definition and there are innumerable connotations attached to it. One of the environmental economists Herman Daly has laid down three essentialities for a sustainable housing framework. These include the rate of use of renewable resources, rate of use of non-renewable resources in the premises and lastly, the controlling of pollution emissions. Also, Dow Jones had developed a sustainability index which delves into the parameters of an ideal sustainable framework. But the parameters mentioned hereunder do not reflect an exhaustive list of things to be included in the sustainable and affordable housing framework.
Dichotomy of affordable-sustainable cities: International outlook
In the international domain, the researcher has critically analyzed three genres of models and decoded the sanctity of the same. The first model which was comprehensively evaluated was the USA model which was marked by Clear Act, 1963 but did not live up to the expectations pertaining to the issue in question. But later, U.S. Department of Housing and Urban Development (HUD) has laid down the criterion for affordable housing by attributing 30% of the gross household income but the sustainability factor was completely ignored. The UK Model brought the Geneva UN Charter on Sustainable Housing in the year 2015 deliberated upon the nuances of sustainability pertaining to housing mechanisms but did not take into consideration the affordability element. Lastly, the Australian Model discussed under the realms of Demographic International Housing Affordability Report of 2015 pointed out the soaring prices of housing facilities so deduced rules of affordable system of housing in the city of Melbourne. But, again one of the things the researcher inferred that there has been a necessary disjunct between affordability and sustainability in various legal institutional paraphernalia.
The Indian approach: A questionable concern
In India, too, the legal mechanism adopted by the government under the realms of Pradhan Mantri Awas Yojana is called as “housing for all”. Under the mandate of the said scheme, the government intended to make houses for everyone at affordable prices. But, this scheme is absolutely silent on the issue of environmental sustainability. The ambiguity emanating out of this scheme needs to be addressed by the government as soon as possible. Even though there have been some governments like that of Trivendrum have been Good Samaritan in this direction by providing sustainable housing facilities at affordable prices as well. Even various private entrepreneurs have now become cautious in respect of their carbon-emissions and have started taking adequate action to substantially reduce them. This is in absolute sync with the Paris Climate Agreement of 2018. Sustainability is not only restricted to controlling and prevention of disparaging of the ecological structure of the world but also, helps in boosting the profits of the company in the long run. Sustainability has become one of the most debatable issues in the modern scenario. Any ideal housing mechanism has to be sustainable and affordable at the same time. Thus, the entire thrust of this research was on developing a sustainable as well as an affordable housing framework for the people in India as well.
But in the post Covid world, the international community needs to re-examine the structures of housing facilities wherein affordability should come in synchronization with the sustainability element as well. Recently, World Health Organization (WHO) deliberated upon the issue of housing so as to de-clutter those ill-made houses so that the spread of highly contagious virus can be contained. Though it has been rightly said by Robert Merton that “It is good to ask questions but it is always better to find solutions to those questions”, but such complex set of questions cannot be answered in one go. They need proper analysis of the problem and then only certain concrete measures could be thought of. The idea behind writing this piece was to ignite the spirit of empathy among the readers about the pitiable condition of the housing. It would be highly falsified on our part if we bombard the readers with a special set of suggestions because the cost-benefit analysis of each of those suggestions would be varied and comprehensive. Thus, I have left the door ajar so that the readers are able to familiarize with the given set of problems which are staring us in this context and then accordingly ponder about the need of sensitization of the sustainable-affordable housing issue at the domestic as well as the global level. The governments have always exhibited callous behaviour towards environment, human rights and public health issues. Thus, a stern eye needs to be kept on these reckless corporate and governmental entities which have only been disparaging the housing issue since time immemorial.
 JM Lavy CONTEMPORARY URBAN PLANNING, Pearson Education Publications 34-39 (4th edition 2009)
 Principle 6, Sustainable Development Goals by United Nations; https://www.undp.org/content/undp/en/home/sustainable-development-goals.html
The Geneva United Nations Charter on Sustainable Housing; https://www.unece.org/fileadmin/DAM/hlm/documents/Publications/UNECE_Charter_EN.pdf
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