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The Sciences

Challenging the Myth: Trees Are Not the Ultimate Solution for Overheating Cities

The cooling effects of trees are complex and vary significantly depending on the context in which they are planted, says researchers

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Image credit: Pixabay

A new study led by the University of Cambridge offers fresh insights into how urban tree canopies, while effective at cooling cities during the day, may inadvertently trap heat at night.

As global temperatures continue to rise, many cities are grappling with the effects of urban heat stress, which is linked to increased illness, energy consumption, and social inequality. Excessive heat can also damage urban infrastructure, highlighting the urgent need for effective mitigation strategies. Among these, tree planting has become a central component of efforts to cool down cities.

However, a recent study led by the University of Cambridge warns that not all tree species or planting methods are equally effective in reducing urban temperatures. According to Dr. Ronita Bardhan, Associate Professor of Sustainable Built Environment at the University of Cambridge’s Department of Architecture, “Trees have a crucial role to play in cooling cities down but we need to plant them much more strategically to maximize the benefits they can provide.”

New Insights on Tree Cooling and Heating Effects

Published in Communications Earth & Environment, the study offers the first comprehensive global assessment of urban tree cooling. By analyzing 182 studies from 110 cities worldwide, the research reveals how tree planting can lower pedestrian-level air temperatures by up to 12°C, with 83% of cities studied achieving temperatures below the “thermal comfort threshold” of 26°C. However, the study also shows that the cooling effects of trees can vary dramatically depending on species, climate, and urban design.

Dr. Bardhan noted, “Our study busts the myth that trees are the ultimate panacea for overheating cities across the globe. The cooling effects of trees are complex and vary significantly depending on the context in which they are planted.”

Cooling Benefits Vary by Climate Type

The study found that urban trees tend to be more effective in cooling cities in hot, dry climates compared to those in humid, tropical areas. In hot and dry climates like Nigeria’s savanna, trees can lower city temperatures by as much as 12°C during the day, but can also increase nighttime temperatures by up to 0.8°C. In arid climates, trees were shown to cool cities by just over 9°C but also raise nighttime temperatures by 0.4°C. Conversely, in tropical rainforest climates, daytime cooling was limited to about 2°C, with nighttime warming reaching 0.8°C.

“Trees perform best in dry, hot climates, but in tropical regions with high humidity, their nighttime warming effect can negate their daytime cooling benefits,” said Dr. Bardhan.

Strategic Tree Planting: The Key to Maximizing Cooling

The study underscores the importance of planting trees in a way that aligns with a city’s specific urban form and climate conditions. Cities with open layouts, for instance, benefit from a mix of evergreen and deciduous trees of varying sizes, leading to more effective cooling across different seasons. In contrast, compact urban layouts, like those in Cairo or Dubai, favor evergreen species that are better suited to dry, hot conditions.

The researchers found that mixed-species planting could provide up to 0.5°C more cooling than monoculture tree planting, as different trees offer varying levels of shade and sunlight penetration at different heights. Furthermore, larger green spaces allow for bigger tree canopies, leading to better overall cooling in dry climates.

“Our study provides context-specific greening guidelines for urban planners to more effectively harness tree cooling in the face of global warming,” Dr. Bardhan said. “Urban planners need to plant the right mix of trees in optimal positions to maximize cooling benefits.”

Looking to the Future: Planning for Warmer Climates

The study also stresses that as climate change progresses, it is essential for cities to choose resilient tree species that will continue to thrive under hotter conditions. “Urban planners should plan for future warmer climates by choosing resilient species which will continue to thrive and maintain cooling benefits,” Dr. Bardhan emphasized.

Furthermore, the researchers note that trees alone cannot solve the issue of urban heat. To complement tree planting, solutions like solar shading and reflective materials should continue to play a vital role in mitigating the heat effects in cities.

A Tool for Urban Planners

In an effort to make these findings more accessible, the researchers have developed an interactive database and map that allows users to estimate the cooling efficacy of different tree planting strategies based on the climate and urban characteristics of cities worldwide. This tool will help urban planners design more effective, climate-specific tree planting schemes.

The Sciences

Indian Scientists Find a New Way to Tune How Metals Interact with Light

Indian researchers have discovered a way to mechanically control how metals interact with light, opening new possibilities for programmable photonic chips and sensors.

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A scientist using a microscope and advanced laboratory equipment during nanophotonics research on the optical properties of metals.

For decades, scientists believed that a metal’s ability to interact with light was fixed once the material was made. Researchers in Bengaluru have now challenged that long-held belief by showing that simply stretching an ultrathin metal film can change its optical properties, a breakthrough that could help develop programmable optical chips and other advanced light-based technologies.

The study, led by researchers at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), is the first to show that mechanical strain can directly change the way a metal responds to light. The findings could lead to reconfigurable photonic devices that work with today’s semiconductor manufacturing methods, making future optical technologies more flexible and energy efficient.

The discovery is based on a phenomenon called plasmon resonance, where free electrons on a metal’s surface move together when light falls on it. This allows light to be concentrated into extremely tiny spaces, making it useful for technologies such as highly sensitive biosensors, medical diagnostics, optical communication systems, imaging devices and photonic chips.

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 Schematic illustration of mechanical control of plasmon resonance in ultrathin films. Image credit: PIB

A key property behind this behavior is the plasma frequency, which determines how a metal responds to light. Scientists have long believed this property depends only on the metal’s composition and cannot be changed after the material is made. Although researchers have found ways to modify a metal’s optical behavior indirectly by changing its structure or surroundings, directly altering the plasma frequency had remained out of reach. The new study shows that mechanical strain can provide a simple new way to achieve this without changing the material itself.

Stretching Metal to Change Its Optical Response

To test their idea, the researchers used ultrathin films of titanium nitride (TiN), a material that is increasingly seen as an alternative to gold because it is more stable at high temperatures, resists chemical damage and is compatible with the manufacturing processes used to make computer chips.

The team produced two identical TiN films, each just 10 nanometres thick. One film was left unchanged, while the other was grown on a specially designed layer that gently stretched the material. This allowed the researchers to study the effect of mechanical strain without changing the metal’s composition.

Using high-resolution electron microscopy, they found that the stretched film responded differently to light than the unstretched one. Computer simulations explained why. Stretching the material made it easier for tiny defects, called nitrogen vacancies, to form inside the crystal. These defects released extra free electrons, increasing the number of electrons available to interact with light and changing the metal’s optical behaviour. Additional spectroscopy and X-ray diffraction experiments confirmed the results.

Why the Discovery Matters

The ability to change a metal’s optical properties using mechanical strain could open new possibilities for photonic technologies, which use light instead of electricity to process and transfer information. Compared with conventional electronics, photonic devices can operate at much higher speeds while using less energy and producing less heat.

Today, most plasmonic devices have fixed properties once they are manufactured. This limits how they can be used. The new approach suggests that future optical devices could be adjusted even after they are made, making them more versatile and easier to adapt for different applications. Such devices could improve optical sensors, imaging systems, communication technologies and next-generation computer chips.

“Our work shows that strain is a powerful and previously underexplored control knob for plasmonic properties in metals,” said Bivas Saha, Associate Professor at JNCASR and the study’s corresponding author. “The ability to mechanically reconfigure the optical response of a CMOS-compatible material like TiN transforms plasmonics from a static platform to an active and programmable one.”

The research also involved collaborators from the University of Sydney, Australia.

Although the study is still at the fundamental research stage, it challenges a long-held understanding of how metals behave and offers scientists a new way to design materials whose optical properties can be adjusted when needed. As demand grows for faster communication systems, artificial intelligence hardware and compact optical devices, the discovery could help lay the groundwork for a new generation of programmable photonic technologies.

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The Sciences

STEM Scholarships for First-Generation College Students: Breaking the Cycle of Poverty

STEM scholarships help first-generation college students access higher education, build careers and break cycles of generational poverty.

STEM scholarships can help first-generation college students overcome financial barriers and pursue careers in science, technology, engineering and mathematics.
Image credit: Stem.T4L/ Unsplash

STEM scholarships are helping first-generation college students overcome financial barriers, access technical education and build careers that can transform families and communities.

In many households across India, the dream of higher education is often overshadowed by the immediate need to make ends meet. For a first-generation college student, earning a university degree is more than a personal achievement; it is a responsibility carried on behalf of an entire family.

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While access to basic education has expanded significantly, entering specialised professional fields remains difficult for students from disadvantaged backgrounds. Science, technology, engineering and mathematics (STEM) disciplines offer one of the most effective pathways out of poverty, yet they are often the hardest to access. The challenge begins long before the first day of college. Talent alone cannot bridge the gap between a modest household and a modern laboratory. Beyond tuition fees, students face a range of hidden costs and barriers that make technical education difficult to pursue.

Without a financial safety net, many capable students are forced to abandon their studies or take up low-skilled jobs to support their families

The Financial Barrier to Technical Education

For a first-generation student, choosing to study engineering, medicine or other STEM disciplines can be a daunting financial decision. Unlike many other degree programmes, STEM courses often involve higher tuition fees, laboratory expenses and intensive academic schedules that leave little time for part-time work.

Without a financial safety net, many capable students are forced to abandon their studies or take up low-skilled jobs to support their families. This is where STEM-focused scholarships can make a meaningful difference.

The most effective scholarship programmes do far more than cover tuition. They often support living expenses, books, learning materials and travel costs. By reducing financial pressure, scholarships allow students to focus on their studies and complete their degrees successfully. Yet financial support alone is only one part of the solution.

Bridging the Skills Gap and Creating Livelihoods

The value of a STEM education extends well beyond individual success. In today’s technology-driven economy, technical skills have become increasingly valuable, opening doors to careers that can transform lives and communities.

First-generation graduates often find opportunities in fast-growing sectors such as healthcare, nursing, pharmacy, engineering and technology. Stable and well-paying jobs can help families move beyond cycles of poverty that may have persisted for generations.

For young women in particular, STEM scholarships can be transformative. Targeted support helps address barriers such as financial constraints, social expectations and unequal access to opportunities.

When a young woman from an underserved community becomes a healthcare professional, engineer or software developer, her success often inspires others around her. The impact extends beyond one individual, encouraging more students to pursue higher education and professional careers. In this way, scholarships help create a new generation of skilled professionals who better reflect the diversity of the society they serve.

Nurturing Growth Beyond the Classroom

There is growing recognition that scholarships should be viewed not simply as financial assistance but as an investment in human potential.

Many first-generation students face uncertainty when transitioning from education to employment. The strongest scholarship models therefore combine financial support with mentorship, career guidance and skills development.

Funding alone is not enough. Students also need exposure to professional environments and opportunities to develop workplace skills. Digital learning platforms, mentoring programmes, skill-building workshops and industry interactions can help bridge this gap.

When students are supported through a broader ecosystem, they are better prepared for life after graduation. They enter the workforce not merely as degree holders but as confident professionals equipped to compete in a rapidly changing economy.

Ultimately, targeted STEM scholarships can turn structural barriers into opportunities. By enabling talented students to access education, develop skills and secure meaningful careers, they help break cycles of generational poverty while contributing to a more equitable and prosperous society.

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Society

When Pollinators Vanish, Children Go Hungry—Here’s the Proof

A landmark study has, for the first time, traced a direct line from the collapse of wild insect pollinators to the malnutrition and poverty of farming families — reframing biodiversity loss as a global public health emergency.

Dipin Damodharan

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Pollinator Decline Threatens Nutrition, Farm Incomes: Study
Image credit: Tom Timberlake

Two billion. That is how many people on this planet eat what smallholder farmers grow. Not what agri-industrial combines harvest, not what commodity markets trade — what families with small plots of land pull from the soil, season after season, with the tools and seeds and knowledge they have. Two billion people. And a significant share of what keeps those harvests coming, what puts vitamins into the food and income into the household, has no name on any payroll, files no tax return, and has never once been thanked.

It is insects. Wild insects — bees, hoverflies, moths, beetles — moving flower to flower across millions of smallholder fields, doing work that no machine replicates and no subsidy replaces. Pollinator decline is dismantling that system quietly, field by field, season by season. A study published today in Nature, led by researchers at the University of Bristol, has for the first time traced exactly what that loss costs — not in abstracted ecosystem valuations, but in the vitamin A missing from a child’s diet, in the folate a pregnant woman never gets, in the farm income that does not arrive at the end of a harvest. The number at the end of that calculation is not a projection or a model. It is a measurement. And it is arresting.

Insect pollinators, the study found, are responsible for 44% of the farming income of the households tracked, and contribute more than 20% of dietary intake of vitamin A, folate and vitamin E — three nutrients whose deficiency is already linked to stunted child growth, weakened immunity and higher rates of disease. When pollinators vanish, the families don’t just grow less food. They grow less nutritious food, earn less money and become more vulnerable to illness. The cycle reinforces itself, downward.

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Ten Villages, One Year, and a Chain of Evidence

The study centred on ten smallholder farming villages and their surrounding landscapes in Nepal. Over the course of a year, the research team — drawn from universities and non-governmental organisations across Nepal, the United Kingdom, the United States and Finland — tracked three things simultaneously: which insects were visiting which crops, what those crops yielded and how nutritious they were, and what the farming families were actually eating and earning.

The impact of pollinator decline on food production and nutrition is high
Nepal’s smallholder farming communities are highly dependent on diverse range of pollinator-dependent crops. Image credit: Tom Timberlake

It is, in structural terms, the kind of study that is very hard to pull off. Most research on pollinators stops at the field boundary — counting bee visits, measuring fruit set, estimating yield differentials. This one kept going, all the way to the dinner table and the household ledger. That continuity of evidence is what makes it significant.

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The picture that emerged was not abstract or statistical. It was human. Over half the children in the study villages were too short for their age — a condition that goes by the clinical name of stunting and signals not just poor growth but compromised brain development, reduced immunity and diminished life prospects. The underlying cause, as the researchers documented it, was diet. And that diet depended, in ways the families could not easily see or control, on the insects working their fields.

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Pollinator Decline: The Hidden Hunger Nobody Is Counting

There is a term in public health circles for the condition that the Nepal families illustrate: hidden hunger. It describes not the obvious, acute starvation that makes headlines, but the chronic, silent insufficiency of vitamins and minerals that undermines health even when enough calories are being consumed. A quarter of the global population currently suffers from it. It is, by most measures, one of the largest sources of preventable illness on the planet, and it is almost entirely invisible in the way society keeps score of environmental damage.

When a species goes extinct, when a forest is cleared, when an insect population crashes — the accounting of loss is typically measured in biodiversity metrics, in ecosystem service valuations, or in the emotional register of what is no longer there to see. It is almost never measured in folate deficiency, in children’s height-for-age charts, in the likelihood of a farming family falling into debt after a bad harvest.

That is what this study changes. It is not the first to establish that pollinator decline matters for nutrition in the abstract. But it is the first to demonstrate, with tracked data from real communities over a real year, the size and mechanism of the effect — and to show that the effect flows not just through calories but through the specific micronutrients that are hardest to replace.

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Biodiversity as Medicine

Planetary Health — the field Dr Myers directs at Johns Hopkins — proceeds from a deceptively simple premise: human health and ecological health are not separate subjects. They are the same subject, studied from different ends. The degradation of natural systems is not a background condition to human development; it is one of the primary mechanisms by which human health is undermined.

That claim has long had intuitive force. What the Bristol study on pollinator decline provides is something more demanding: empirical evidence at the household level. It is one thing to argue that biodiversity loss will eventually compromise food security in a generalised way. It is another to show, village by village, season by season, that the decline in the bee community visiting a particular set of crops reduces particular vitamins in particular families’ diets by a measurable amount.

Bee on a flowering crop showing the impact of pollinator decline on food production and nutrition
Image credit: Tom Timberlake

The phrasing matters. Biodiversity is not a luxury. In policy conversations, the language of luxury — or alternatively, of long-term concern — has frequently served to push ecological questions down the agenda. If the relationship between pollinator health and child health is as direct as this study finds, that framing becomes harder to sustain.

What Goes When the Bees Go

It is worth being specific about the nutritional stakes. Vitamin A deficiency impairs vision, particularly in low light, and compromises the immune system’s ability to fight infections that would otherwise be routine. Folate deficiency during pregnancy causes neural tube defects in developing foetuses, among other effects. Vitamin E is a key antioxidant, and its deficiency is associated with neurological damage and weakened immune function. These are not marginal health concerns. They sit near the top of the global burden of preventable disease.

The crops most dependent on animal pollination — fruits, many vegetables, pulses — are also, not coincidentally, among the most concentrated sources of these particular nutrients. A diet from which pollinator-dependent produce has been reduced or removed can look adequate in calorie terms while being profoundly inadequate in micronutrient terms. The families studied in Nepal were, in effect, already living that deficit, in a context where pollinator diversity is declining.

Globally, insect populations have been under sustained pressure for decades. Pesticide use, habitat loss, monoculture farming, climate change and artificial light at night have all been implicated in declines that researchers have called, in some cases, ecological collapse. The mechanisms are various; the direction of travel is consistent.

The Good News: Reversible by Design

The research is, in its implications, genuinely alarming. But the researchers are also at pains to emphasise something that is easy to miss in the headline findings: the relationship between pollinators and nutrition runs in both directions. If pollinator decline causes nutritional harm, pollinator recovery can produce nutritional gains. And the actions required are not exotic.

Planting wildflowers at field margins. Reducing pesticide inputs. Keeping native bee colonies. These are the kinds of changes that do not require new technology or large capital investment. They require farmers to understand what is happening in their fields at a level of detail most have not previously been given reason to consider. The researchers are already working on that — translating their findings into practical guidance and working with local organisations, government partners and farmers in Nepal to implement changes on the ground.

The approach is now informing Nepal’s emerging National Pollinator Strategy, an effort to make pollinator-friendly practices a standard part of everyday agriculture rather than a specialist conservation concern. The researchers report that farmers who have adopted even modest changes are already seeing improvements in crop yields, income and nutrition — a feedback loop that runs in the direction of health rather than away from it.

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A Framework That Travels

Nepal is not an isolated case. Two billion people around the world depend on smallholder farming. Many of them face the same combination of circumstances: high dependence on pollinator-sensitive crops, limited dietary alternatives, micronutrient deficiencies that are already entrenched and ecosystems under stress. The findings from ten Nepali villages do not translate automatically to every agricultural context, but the framework — the method of tracing connections from insects to income to nutrition — does.

Diets even in industrialised countries still depend on pollinators and the ecosystems that sustain global agriculture. The buffer of wealth — the ability to import, substitute, supplement — is larger in wealthy countries, but it is not unlimited, and it does not protect the most economically vulnerable people even within those countries.

The lesson from this research on pollinator decline is less a specific warning about Nepal and more a methodological call to arms: to start measuring the connections that have, until now, been assumed or asserted but rarely demonstrated. When those connections are demonstrated, the case for protecting what remains of insect diversity becomes something different — not a moral preference or an aesthetic value, but a documented precondition for human health.

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The Stakes

A quarter of the world’s people are living with hidden hunger. Over half the children in ten Nepali villages are stunted. Forty-four percent of the farming income in those communities flows, invisibly, through the wings of insects that nobody counted or protected until researchers started looking. The insects are in decline.

The study’s authors are careful, as scientists should be, to describe what they found and what it implies rather than what must be done. But the shape of the implication is not obscure. The fabric of life — the phrase Dr Myers uses — is not an abstraction. It is the thing that puts vitamins in a child’s diet and money in a family’s pocket. Tear large enough holes in it, and the consequences are not primarily ecological. They are medical. They are economic. They are, in the most direct sense, human. That’s why the new findings on pollinator decline matter.

The bees were always doing the work. We just weren’t watching closely enough to see it — or to understand what we stood to lose.

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