Experts hail rapid transformation that will see clean energy outgrow fossil fuels in the next five years - but warn UK is failing to exploit huge potential.

Green energy accounted for more than half of net electricity generation capacity added around the world last year for the first time, leading energy experts have found.

The International Energy Agency (IEA) said the milestone was evidence of a rapid transformation in energy taking place, and predicted capacity from renewable sources will grow faster than oil, gas, coal or nuclear power in the next five years.

But the analysts said the outlook in the UK has deteriorated since the Conservative government took power last year and cut support for wind and solarpower. The agency’s chief said Britain had huge renewable energy potential and ministers needed to design stronger policies to exploit it.

“What I see is we are witnessing the transformation of energy system markets led by renewables and this is happening very quickly,” said Dr Fatih Birol, executive director of the IEA. “This transformation and the growth of renewables is led by the emerging countries in the years to come, rather than the industrialised countries.”

China will lead the world for growth in renewable power, followed by the US and Europe, a new report by the agency found. The IEA said the EU was relinquishing its position as a renewable energy pioneer due to weak electricity demand and policy uncertainty, which Birol warned could see European renewable energy manufacturers lose out to international rivals.

“If you think of running a marathon, Europe started with a big advance, more than half of the marathon they are leading by far. They are now getting a bit tired, and some others are overtaking Europe slowly but surely,” he told the Guardian.

The IEA said Asia will be the “engine of growth”, led by China and India. “China is a completely separate chapter,” said Birol. “China alone is responsible for about 40% of growth in the next five years. When people talk about China, they think about coal, but it is changing.”

A total of 153GW of net renewable electricity capacity was installed globally in 2015, a record high, equivalent to Canada’s capacity and up 15% on the year before. Net capacity is new capacity minus retired capacity, such as old hydro being taken offline. China is expected to add a further 305GW over the next five years, followed by India with 76GW.

Onshore windfarms and solar power led the charge last year, with 63GW and 49GW of new global capacity respectively. The two technologies are also forecast to take the lion’s share of growth, with electricity generation from solar tripling and wind doubling.

Their costs are expected to continue the dramatic and unprecedented reductions in recent years, with onshore wind coming down a further 15% and big solar 25% by 2021.

“The cost of wind dropped by about one third in the last five to six years, and that of solar dropped by 80%,” said Birol, adding that while the cost of gas had also fallen recently, it was not at the same speed that green energy had become cheaper. “The decline in renewables [cost] was very sharp and in a very short period of time. This is unprecedented.”

While renewables now account for more than 50% of net capacity additions and are expected by the IEA to reach around 60% by 2021, they still provide a relatively small share of the world’s electricity. Green sources are only expected to provide 28% of electricity generation by 2021, up from 23% in 2015, and much of that will be from existing hydropower dams.

Renewable energy is seen by scores of countries as a key way to meet climate targets that they pledged under the Paris agreement, which comes into force in November.

But even with the huge growth expected in coming years, the IEA said it will not be sufficient to meet the Paris deal’s target of keeping temperatures below 2C, the threshold for dangerous warming. “No, it’s by far not enough [the trajectory of growth],” said Birol.

The agency painted a gloomy picture of solar and onshore wind’s prospects in the UK, echoing recent warnings from other respected energy authorities. “The policy landscape for renewables has become more challenging since the 2015 general election,” the report said.

Since coming to power, the Conservatives have drastically cut or ended subsidies for wind and solar power, begun the privatisation of the green bank which supports clean energy, and enthusiastically backed fracking for shale gas and new nuclear. “While government support for new gas and nuclear capacity is evident, recent policy changes indicate that the role envisioned for renewables is uncertain,” the IEA said.

“There is need in the UK to invest in stronger renewable policies,” said Birol. “The potential is huge compared to what we are expecting.”

The agency’s chief said that contrary to what renewable energy critics argued, the biggest threat to the technologies was not their intermittent nature but the intermittency of governments’ support.

“The issue is not the predictability of solar and wind, it is the predictability of government policies because investors need to see what their prospects are. This is the main challenge I see in the renewable energy sector.”

Imke Lübbeke, head of climate and energy at WWF’s European policy office, said: “The IEA report clearly shows that president [Jean-Claude] Juncker’s promise to make the EU ‘the world leader in renewables’ remains empty rhetoric. Instead, the European Union is losing its leadership role to the US and China.”

This article was originally posted on the Guardian.

Cities are like magnets. Without a better model for growth, people will still come – but they will live in awful conditions. This year’s Pritzker prize-winning architect presents his legal, financial and design roadmap to a new urban reality.

In Quito as many as 45,000 people have gathered for Habitat III, the global UN summit which, every 20 years, resets the world’s urban agenda.

Why should we care? Well, to start with, in the next 20 years, we will witness more than two billion more people moving to cities. Depending on what we do to accommodate them, this could be good – or very bad – news.

It’s good news because people are demonstrably better off in cities than outside them. For the poor, cities are efficient vehicles to satisfy basic needs. Having people in a concentrated space makes the implementation of public policies more effective (think of access to sanitation, and the consequences for reducing child mortality and epidemic disease).

For the middle class, meanwhile, cities are a concentration of opportunities for jobs, education, healthcare and even recreation. They offer the promise of social mobility. And for a certain elite, cities are a powerful vehicle to create wealth; their critical mass generates the appropriate environment for knowledge creation and prosperity in the broadest sense of the word.

In short, cities are like magnets, with the potential to take care of everything from the most basic needs to the most intangible desires.

Now for the bad news, which we could call the “3S menace”. The scale and speed of this global urbanisation, and the scarcity of means with which we must respond to it, has no precedents in human history.

Of the three billion urban dwellers today, one billion live below the poverty line. In two decades’ time, five billion people will be in cities, with two billion of them below the poverty line.

To accommodate such growth humanely, we would need to build a city of one million people every week, spending no more than $10,000 per family. If we don’t solve this equation, it’s not that people will stop coming to cities; they will still come, but they will live in awful conditions.

What’s at stake here is not just poverty but inequality too. Cities express in a very concrete and direct way the distance between the haves and have-nots.

Urban inequalities are often reflected in brutal ways – from the distance people must travel to work every day, to the lack of quality public spaces, urban amenities and civic services. No wonder so much anger and resentment is accumulated in the peripheries.

Of course, this is problem is not exclusive to developing countries. Rich countries, despite having solved all their basic needs, experience a similar accumulation of social pressure as if it was a ticking time bomb.

A way to grow

To add one more level of complexity to the phenomenon of urbanisation, even if we do eventually find a way to build for that extra million people each week, we will go into environmental crisis, such is the carbon footprint of today’s construction process.

This would not only be a “green” problem, but a major security threat too. According to a report by the US defence department, the next conflicts, wars and terrorist threats will be triggered by climate change.

There is a one-to-one correlation between zones of military conflict and a global map of water drought. This not only creates problems in the afflicted countries but also migrations towards less-affected areas, adding to the social pressure in the countries of destination too.

These are the kind of challenges that needed to be addressed at Habitat III. Fortunately, an appeal by Dr Joan Clos, the executive director of UN Habitat appointed by Ban Ki Moon to guide the event, already carries a promising approach.

Clos’s framing of the problem can be synthesised like this: we need to invert the way we view the relationship between economic development and good cities.

The current approach is: first a country creates wealth. Once that is achieved, good cities will follow automatically, becoming a kind of passive outcome of economic development.

Clos’s task has instead been to convince the world’s mayors (and development experts, and ministers of finance) that good cities can be a source of development, rather than the other way around. This reframing, and what results from it, can be summarised as follows …

Lesson 1: good cities may be the source, instead of the passive outcome, of economic development

For this inversion of the paradigm to take place, however, you need three things: the right rule of law, the right financial plan and the right design. Imagine the mayor of City X in a rather poor country (which is, of course, where the majority of future urbanisation will take place). He or she may look out of their window and see an informal settlement growing by the hour.

Regarding the rule of law: in this settlement, property rights are unclear, so the shacks that actually cost quite a bit of money cannot have a “parallel life as capital”, as the economist Hernando de Soto puts it. Regarding the financing: there is only one source – people’s own resources. And regarding design: there is no access to sanitation, so no clean water nor sewerage system.

There is no creation of value here, merely expense. The proportion between public and private space in such spontaneous urbanisation is invariably less than 1:10. Evidence shows that only when this ratio is close to 1:1 can one expect some value gain for residents (Manhattan is the ultimate example of this). . In such cases, each individual action not only gains individual value but also adds to the common good. In a slum, individual interventions, however well intentioned, cannot guarantee that.

Lesson 2: the scarcest resource in cities is not money, but coordination

There is one good side to the informality of the city growing outside the mayor’s window. Since it is spontaneous, there is no zoning regulation (a kind of fundamental truth of planning). Instead, we can expect a richly mixed fledgling city, where residential, businesses, retail services and productive activities all coexist together.

The interior of a ‘half house’ by Aravena, before and after. Photograph: Tadeuz Jalocha
 

Lesson 3: a certain urban intensity is desirable
Now our mayor ponders: what can I do with an annual budget of just $6 per inhabitant to invest in this new city? Once again, this financial plan has only one source: a state with scarce resources. Such a limited budget may force our mayor to transform agricultural land into urban land, adding to the already underserved peripheries and expanding the sprawl.

The mayor will likely devote only a very small area to public space (as little as 20%) so more land can be dedicated to accommodating the mass of people that are pressing to be given a house. Zoning regulations will very likely be applied, resulting in a separation of functions and a very low urban intensity. Finally, since the tight budget won’t allow to build “middle-class standard” housing units, evidence shows that as much as 50% of the built environment will be self-built all the same (despite, not thanks to, the design of the units).

Facing this adverse scenario, a private real-estate developer may approach the mayor of City X and request, say, 20 hectares of land to build a housing project. And the mayor, spotting the opportunity for someone else to take care of his housing headache, may make a counter-offer: that the project will only be approved on the condition the developer actually takes 40 hectares of land.

Naturally the developer will agree, then proceed as usual: property rights will be secured and zoning regulations complied with, resulting in low urban intensity. The financing plan will still depend on one source – this time private capital, which will look for a two-digit return in a short period of time.

Such a miserly way of investing will dedicate as little area as possible to public space (again, as little as 20%) in order to maximise the area that can be sold. The developer may add some meandering streets to make the urban footprint more appealing, and some decoration to the tiny units. But design-wise, the contribution of the private market will be like putting lipstick on a gorilla.

So, what to do? Perhaps the mayor of City X has come to Quito looking for clues, ideas and tips. And one could be to join up the forces of the (poor) state and the (mediocre) developer, without expecting either of them to change their nature.

Rather than giving away a whole slab of land as a closed package, the mayor could instead partition the area the developer is asking for, then create reserves of public space between the lots: ecological corridors with a civic standard the developer would never be incentivised to deliver.

The developer would then follow his usual model, adding a further 20% of public space – so that, overall, the project now possesses a much more liveable 40% of public space.

For this scheme, the financial plan now has two sources: state funding, to take care of the public space and eventually some urban services too, and private funding, which looks after the urbanisation and some public space as well. Such a development will still have low urban intensity, but the higher ratio of public space may open it up to some value gain in future.

The crucial point here is to secure the “void” of the future city. The quality of its residents’ future mobility, for example, will depend on the quality of the space we reserve in between the buildings.

Lesson 4: in a “good” city, what is not built is more important than what is

An even greater disruption from the predictable, mediocre norm would be for the state and the market to join forces with people’s own resources.

To allow the inclusion of a third source in the financial plan, the design has to be an open one. The starting point would be the same as the previous one: public space reserved between the conventional real estate. But the developer should then be required leave 50% of the lots not built.

In such a scheme, these voids are intended to channel people’s own initiative – and, consequently, their resources. Property rights will be secured, but the “porosity” of the structures allows them to be customised, and leaves room for a higher level of urban intensity in the future. The process of reaching a middle-class standard through self-construction will happen thanks to the design, not despite of it.

Lesson 5: people’s own building capacity is part of the solution, not the problem

As Habitat III draws to a close this week, I wonder whether by 2036, when the next Habitat conference comes around, Clos’s “paradigm shift” will have gained traction among decision-makers. I hope the real-estate world will have moved from its current, standard two-digit return to a (fair enough) one-digit return which prioritises predictability over profitability in the way developers invest in cities.

This blog post was originally posted on the Guardian.

The rapid transformation of farming and food systems to cope with a warmer world, such as adopting climate-smart practices, particularly to curb greenhouse gas emissions, is critical for hunger and poverty reduction, the United Nations agriculture agency said today in a new report.

“There is no doubt climate change affects food security,” said the Director-General of the Food and Agriculture Organization (FAO), José Graziano da Silva, as he presented The State of Food and Agriculture 2016 report at the agency’s headquarters in Rome.

“What climate change does is to bring back uncertainties from the time we were all hunter gatherers. We cannot assure any more that we will have the harvest we have planted,” headded.

That uncertainty also translates into volatile food prices, he noted. “Everybody is paying for that, not only those suffering from droughts,” Mr. Graziano da Silva said.

FAO warns that a ‘business as usual’ approach could put millions more people at risk of hunger, than in a future without climate change. Most affected would be populations in poor areas in sub-Saharan Africa and South and Southeast Asia, especially those who rely on agriculture for their livelihoods. Future food security in many countries will worsen if no action is taken today.

“The benefits of adaptation outweigh the costs of inaction by very wide margins,” emphasized Mr. Graziano da Silva.

However, it is agriculture, including forestry, fisheries and livestock production, which is contributing to a warmer world by generating around a fifth of the world’s greenhouse gas emissions. Therefore, agriculture must both contribute more to combating climate change while bracing to overcome its impacts, the report says.

Time for action

Without action, agriculture will continue to be a major contributor to global greenhouse gas emissions. But by adopting climate-smart practices and increasing the capacity of soils and forests to sequester carbon, emissions can be reduced while stepping up food production to feed the world’s growing population, the report says.

The report provides evidence that adoption of climate-smart practices, such as the use of nitrogen-efficient and heat-tolerant crop varieties, zero-tillage and integrated soil fertility management would boost productivity and farmers’ incomes. Widespread adoption of nitrogen-efficient practices alone would reduce the number of people at risk of undernourishment by more than 100 million, the report estimates.

It also identifies avenues to lower emission intensity from agriculture. Water-conserving alternatives to the flooding of rice paddies can slash methane emissions by 45 per cent, while emissions from the livestock sector can be reduced by up to 41 per cent through the adoption of more efficient practices.

“2016 should be about putting commitments into action,” urged Mr. Graziano da Silva, noting the international community last year agreed to the Sustainable Development Goals (SDGs) and the Paris Agreement on climate change, which is expect to come into force early next month. Agriculture will be high on the agenda at the 22nd Conference of the Parties to the UN Framework Convention on Climate Change (UNFCCC), known by the shorthand COP 22, in Morocco starting on 7 November.

Helping small farmers adapt to climate change risks is critical

Developing countries are home to around half a billion small farm families who produce food and other agricultural products in greatly varying agro-ecological and socio-economic conditions. Solutions have to be tailored to those conditions; there is no one-size-fits-all fix.

Helping smallholders adapt to climate change risks is critical for global poverty reduction and food security. Close attention should be paid to removing obstacles they may face and fostering an enabling environment for individual, joint and collective action, according to the report.

FAO urges policy makers to identify and remove such barriers. These obstacles can include input subsidies that promote unsustainable farming practices, poorly aligned incentives and inadequate access to markets, credit, extension services and social protection programmes, and often disadvantage women, who make up to 43 per cent of the agricultural labour force.

The report stresses that more climate finance is needed to fund developing countries’ actions on climate change. International public finance for climate change adaptation and mitigation is growing and, while still relatively small, can act as a catalyst to leverage larger flows of public and private investments. More climate finance needs to flow to sustainable agriculture, fisheries and forestry to fund the large-scale transformation and the development of climate-smart food production systems.

This article was originally posted here.

A growing global population and changing diets are driving up the demand for food. Production is struggling to keep up as crop yields level off in many parts of the world, ocean health declines, and natural resources—including soils, water and biodiversity—are stretched dangerously thin. One in nine people suffers from chronic hunger and 12.9 percent of the population in developing countries is undernourished. The food security challenge will only become more difficult, as the world will need to produce about 70% more food by 2050 to feed an estimated 9 billion people.

The challenge is intensified by agriculture’s extreme vulnerability to climate change. Climate change’s negative impacts are already being felt, in the form of reduced yields and more frequent extreme weather events, affecting crops and livestock alike. Substantial investments in adaptation will be required to maintain current yields and to achieve the required production increases

Agriculture is also a major part of the climate problem. It currently generates 25% of total greenhouse gas emissions. Without action, that percentage could rise substantially as other sectors reduce their emissions.

Producing More with Less

Climate-smart agriculture (CSA) is an integrated approach to managing landscapes—cropland, livestock, forests and fisheries--that address the interlinked challenges of food security and climate change. CSA aims to simultaneously achieve three outcomes:

1.    Increased productivity: Produce more food to improve food and nutrition security and boost the incomes of 75% of the world’s poor, many of whom rely on agriculture for their livelihoods.

2.    Enhanced resilience: Reduce vulnerability to drought, pests, disease and other shocks; and improve capacity to adapt and grow in the face of longer-term stresses like shortened seasons and erratic weather patterns.

3.    Reduced emissions: Pursue lower emissions for each calorie or kilo of food produced, avoid deforestation from agriculture and identify ways to suck carbon out of the atmosphere.

While built on existing knowledge, technologies, and principles of sustainable agriculture, CSA is distinct in several ways. First, it has an explicit focus on addressing climate change. Second, CSA systematically considers the synergies and tradeoffs that exist between productivity, adaptation and mitigation, in order to capitalize on the benefits of integrated and interrelated results.

Find out more about CSA basics, planning, financing, investing and more in the online guide to CSA developed in collaboration with the Research Program on Climate Change, Agriculture, and Food Security (CCAFS) of the Consultative Group on International Agricultural Research (CGIAR): https://CSA.guide.

Climate-Smart Agriculture and the World Bank Group

The World Bank Group (WBG) is currently scaling up climate-smart agriculture and in its Climate Change Action Plan has committed to 100 percent of agricultural operations being climate-smart by 2019. The WBG portfolio will also increase its focus on impact at scale and be rebalanced to have a greater focus on adaptation and resilience. To enable these commitments, we are screening  all IDA projects for climate risks, and will continue to develop and mainstream metrics and indicators to measure outcomes, and account for greenhouse gas emissions in our projects and operations. These actions will help our client countries implement their Nationally Determined Contributions (NDCs) in the agriculture sector, and will contribute to progress on the Sustainable Development Goals for climate action, poverty, and the eradication of hunger.

The World Bank Group also backs research programs such as the Consultative Group on International Agricultural Research (CGIAR), which develops climate smart technologies and management methods, early warning systems, risk insurance and other innovations that promote resilience and combat climate change.

For example, Climate-Smart Agriculture (CSA) Country Profiles bridge a knowledge gap by providing clarity on CSA terminology, components, relevant issues, and how to contextualize it under different country conditions. The knowledge product is also a methodology for assessing a baseline on climate-smart agriculture at the country level (both national and sub-national) that can guide climate smart investments and development.

Working Toward Food and Nutrition Security, while Curbing GHG Emissions

The Bank’s support of CSA is making a difference across the globe:

In Uruguay, the Sustainable Management of Natural Resources and Climate Change (DACC) project is supporting sustainable intensification through a number of initiatives including the establishment of an Agricultural Information and Decision Support System (SNIA) and the preparation of soil management plans.

The Morocco Inclusive Green Growth project supports the national green growth agenda by increasing the supply of agrometeorological information and facilitating the diffusion of new, resilience-building technologies such as direct seeders.

In Senegal, the West Africa Agricultural Productivity Program (WAAPP) and its partners have developed seven new high-yielding, early-maturing, drought resistant varieties of sorghum and millet. Released in 2012, these varieties are being widely diffused to farmers and show positive yield result.

In Ethiopia, the Humbo Assisted Natural Regeneration Project has helped restore 2,700 hectares of biodiverse native forest, which has boosted production of income-generating wood and tree products such as honey and fruit.

African farmers who have adopted evergreen agriculture are reaping impressive results without the use of costly fertilizers. Crop yields often increase by 30 percent and sometimes more. In Zambia, for example, maize yields tripled when grown under Faidherbia trees..

This blog post was originally posted here.

With water shortages exacerbating inequalities and causing damage to economies, making sure the commodity is properly valued by all is essential.

Water is essential for life, whether to irrigate crops, to manufacture goods, or for drinking, washing and cleaning. But the intensification of climate change, a growing population and increasing demands from cities, agriculture and industry – coupled with poor water governance – is driving acute water shortages around the world.

The World Bank predicts that by 2050 this scarcity will deliver a significant hit to the economies of Africa, central Asia and the Middle East, taking double digits off their GDP.

To address these challenges and ensure that every person, country and business has enough, it is essential to determine the true value of water throughout the supply chain. But how?

This was the question debated during a panel discussion, hosted by the Guardian and supported by SABMiller, at the World Water Week conference in Stockholm, Sweden, which was organised in association with the Stockholm International Water Institute (SIWI).

Lack of awareness

John Vidal, the Guardian’s Environment editor who chaired the debate, asked whether farmers need to think differently about how they grow and irrigate crops, if they are unwilling or unable to pay for water.

“I think it’s already happening,” said Anton Earle, director of SIWI’s African Regional Centre. The government of Botswana is looking at ways to introduce a water charge for farmers and the farmers SIWI speaks to there say they are already using efficient techniques for irrigation to reduce the cost of powering pumps, he said.

Speaking companies’ language

It is not only in agriculture, however, where operations and processes need to be more water efficient.

SIWI has been working with Swedish textile companies to encourage their production plants in countries such as Bangladesh, China and Ethiopia to place greater value on water. “We talk to these factories and say: ‘You’re using and polluting many of the water resources in the local area – you should change your practices’, but factory owners would rather sell to a business that is less pushy,” said Earle.

Instead, the key was to find the right language businesses could respond to. “We asked them about their major costs and they consistently pointed to energy and the chemicals used to dye textiles. We told them we could introduce processes that would reduce those costs,” said Earle. “So instead of dyeing fabric three or four times and releasing the water, they do it once, capture the chemicals and reuse them. Improving water use is a side effect but the entry point had to be something that the corporates could really relate to.”

But individual corporate action does not necessarily mean water is being better valued overall. André Fourie, head of water security and environmental value at SABMiller, described the company’s work with barley farmers in India, where he says agriculture accounts for 80% of water consumption. “By having better irrigation – drip irrigation [where water is directed at the plant’s root], for example – they save water. But we’ve also seen that the water they save is used by someone else, so we haven’t actually solved the problem.”

One of the most effective ways for companies to determine the value of water, says Fourie, is to develop a better understanding of what it costs throughout different parts of the business. “By having one price [for water] in our thinking it makes our decisions quite blunt. Take a brewery: the water that comes into it has one price, but if the brewery treats it the water is worth more.”

Should we pay more for water?

One of the key challenges in securing a long-term supply of water is finding sustainable streams of finance and working out who should bear the cost.

“In many cases, there is a cultural issue around making profit from water, even in countries where the private sector has played a strong role in different parts of the economy,” said Earle.

When it was suggested to the National Treasury of South Africa that the country’s wastewater treatment could be handled by the private sector on the condition that the business could sell off the treated water, the idea, said Earle, was not met with open arms.

In some areas, however, many of the poorest people have to buy water from vendors, tankers and other informal providers, and spend as much as 10 times more than someone who has a reliable connection in the home. While this situation reveals deep inequalities, it also shows that there is a willingness to pay.

Monika Freyman, director of Investor Water Initiatives at non-profit Ceres, agreed that asking domestic users to pay for water could be a way of increasing the value placed on it, as well as leveraging the money needed to secure supply.

“Many investors, when they look at private solutions or public-private partnerships, are beginning to ask: ‘How can we ensure that those at the bottom of the pyramid can afford and have access to water?’ I think privatisation can work but you have to have pretty strong policies and stewardship from the regulators to go with it.”

Freyman believes that the corporate and investment community can value water better by understanding the risks of inefficient water management. “Many companies are beginning to assess the money they’re leaving on the table by not getting water management right,” she said. “In the past, the investment community was obsessed with the volumes of water they were using, but I think the bigger question now is: what are the lost opportunities around not understanding and managing water well?”

This article was originally posted on the Guardian.

Mature trees clean air, lower stress, boost happiness, reduce flood risk – and even save municipal money. So why are they cut down when cities develop – and how should the UN’s new urban agenda protect them?

The skyline along Manhattan’s Upper Fifth Avenue, where it flanks Central Park, is dominated by vast, verdant clouds of American elm trees. Their high-arched branches and luminous green canopies form – as historian Jill Jones puts it – “a beautiful cathedral of shade”. When she started researching her new book, Urban Forests, she’d have struggled to identify the species – but now, she says, “when I see one, I say ‘Oh my goodness, this is a rare survivor,’ and deeply appreciate the fact that it’s there.”

The American elm was once America’s most beloved and abundant city tree. It liked urban soil, and its branches spread out a safe distance above traffic, to provide the dappled shade that cities depended on before air conditioning.

Now, however, most of the big, old elms have been wiped out by Dutch elm disease. Many of them were replaced by ash, which have in turn been killed by another imported pest: the emerald ash borer. By the 1970s, writes Jones, much of America’s urban tree cover had fallen victim to “disease, development and shrinking municipal budgets”.

Thousands of miles away, in Bangkok, the main threat is construction work. After a group of residents tried in vain to save several mature trees on their lane, which were felled to make way for a car park, they formed a tree advocacy group, the Big Trees Project.

Within weeks, membership swelled to 16,000. Forestry officer at the Food and Agriculture Organisation of the United Nations (FAO), Simone Borelli tells me of similar tree advocacy groups in Malaysia, India and Central African Republic, where the capital, Bangui, has “grown out of the forest and is eating it up”.

This month will see representatives from the world’s cities convene in Quito, Ecuador, for the United Nations conference on sustainable urban development,Habitat III. An agreement called the New Urban Agenda will be launched, to address the challenges facing a growing global urban population that already accounts for over 50% of us.

The document is littered with references to green spaces being essential for mental and physical health, community building and performing urgent ecological tasks. Research has turned up fascinating evidence as to why town councils, planners and developers – in whose hands the fate of urban trees lies – should take heed.

Until recently, says Jones, city officials saw trees as “expensive ornaments”. But what is now known about the ecological services that trees provide is staggering.

Trees can cool cities by between 2C and 8C. When planted near buildings, trees can cut air conditioning use by 30%, and, according to the UN Urban Forestry office, reduce heating energy use by a further 20-50%. One large tree can absorb 150kg of carbon dioxide a year, as well as filter some of the airborne pollutants, including fine particulates.

It’s hard to put a price on how an avenue of plane trees can muffle the roar of a main road, although trees do on average increase the value of property by 20%. Perhaps money does grow on them after all.

When the New York City park department measured the economic impact of its trees, the benefits added up to $120m a year. (Compare that to the $22m annual parks department expenditure.) There were $28m worth of energy savings, $5m worth of air quality improvements and $36m of costs avoided in mitigating storm water flooding. If you look at a big tree, says Jones, “it’s intercepting 1,432 gallons of water in the course of a year.”

Use of the open source software, i-Tree, has spread all over the world (from China to the UK, via Brazil and Taiwan) to assess canopy size – ideally, cities should have 40% coverage – and calculate its economic worth. “To be able to monetise those benefits is really useful,” says Jones. “Trees are economic drivers. Everyone knows, if you look at fancy neighbourhoods, they are the ones with the most trees.” By the same token, she observes that underprivileged neighbourhoods are often also undercanopied.

Humans are drawn to trees by more than aesthetics. It can bring down cortisol levels in walkers, which means less stress. The effect on our brains is a subject that fascinates UK-based GP and public health expert William Bird.

“The parts of our brain we use change when we connect with nature,” he says. Even in lab-based studies, MRI scanning shows that when viewing urban scenes, blood flow to the amygdala – the “fight-or-flight” part of the brain – increases. Our brains view cities as hostile environments. Natural scenes, by contrast, light up the anterior cingulate and the insula, where empathy and altruism happen.

“In areas with more trees,” says Bird, “people get out more, they know their neighbours more, they have less anxiety and depression.” (Here in the UK, the annual mental health bill is around £70bn.) “Being less stressed,” he continues, “gives them more energy to be active”. But you can’t fob people off with an empty playing field, he says. “People won’t want to go there. We are still programmed as hunter gatherers who look for trees, biodiversity, water and safety.”

Research suggests people are less violent when they live near trees. One of the oft-cited examples is a study that looked at women in a Chicago housing estate. Those who lived near the trees reported less mental fatigue and less violent tendencies than those in barren areas of the same estate.

“We still know very little about the mechanisms linking trees and health,” says Geoffrey Donovan, research forester with the US Forest Service. But there are theories. One is that nature is so mentally restorative that it gives our minds a rest from the forced, direct attention that modern life and urban environments increasingly call for. It relieves mental fatigue.

A tree psychology study that particularly tickles Jones was done in Toronto bypsychology professor Marc Berman, using data sets from the national health system. “He discovered that, if you have 10 more trees on a city block, it improves health perception as much as having £10,000 more in income, or feeling seven years younger,” she says.

Perhaps one of the most striking studies on urban trees is one that showed that they reduce health inequality. In 2008, Rich Mitchell, a public health professor at the University of Glasgow, compared income deprivation and green space exposure across England and his study found “health inequalities related to income deprivation in all-cause mortality and mortality from circulatory diseases were lower in populations living in the greenest areas”.

Back at the US Forest Service, Donovan refers to trees as “a matter of life and death”. “I looked at the impact of trees on birth outcomes and found that mothers with more trees within 50m of their homes are less likely to have underweight babies,” he says. For another study, he looked at mortality rates in areas which have lost millions of trees to emerald ash borer, and identified “a corresponding increase in human mortality”.

The value we place on trees and nature is informed by childhood experience. Children growing up dislocated from nature results in, say some researchers, an “extinction of experience”. These children will ultimately understand and value nature less. “This means,” writes Bird, “that each generation will pass on less experience of the natural environment – and as policymakers and future environmentalists they will have a poorer understanding of nature and so give it less value”.

Which would not bode well for the FAO Forestry Department’s vision of “greener, happier, healthier cities”. As Jones says, “being an amateur tree appreciator, as I now am, really does transform your enjoyment of being out and about”.

This article was originally posted on the Guardian.