How trees saved 153 lives in London in eight years – inews

Trees are already much loved for improving our mood and helping the environment. Now, a study suggests they are also quite literally saving hundreds of lives in cities across the UK.

In London trees have saved more than 150 lives in eight years by cutting temperatures in large swathes of the city by up to 2C, researchers estimate.

And they say a similar tree-cooling process is taking place in urban environments around the country.

Urban areas are often several degrees warmer than rural areas – in large part because the darker surfaces of roads and buildings absorb larger amounts of the sun’s heat, but trees go some way to easing high temperatures in built up places.

The study estimated that 16people in London were saved during the summer heatwaves of 2022, as trees reduced deaths from causes such as dehydration, heat strokes and heart failure that stem from the body’s inability to cool down sufficiently.

The trees did this by cooling down the temperature by up to 2C. They do this by reflecting sunlight back into the sky with their leaves, by shading the area underneath the canopy and by producing water vapour – a process which uses the sun’s warmth to evaporate water in the leaves and branches, thereby taking that heat out of the surroundings.

Report author Oscar Brousse, of University College London, said: “Our study shows that trees could save lives during heatwaves and hot summers.

“That is one thing. But trees are also known for other benefits like being good for our mental health, encouraging physical activity or even reducing our blood pressure and cardiac rhythm – all of this while sucking out CO2 from the air, improving water retention and providing shelter to fauna and flora.”

Researchers were able to estimate the number of lives saved by looking at records of excess deaths at various temperatures and pairing that with data about how much the trees reduced temperatures.

Dr Brousse’s study only looked at London and did not estimate the number of lives that trees could save across the country, in part because population and tree density vary considerably from one area to another.

But he said that, based on the London findings, it would be fair to estimate that “hundreds of lives could probably have been saved across cities in the UK” over the eight years of the study, which ran from 2015 to 2022.

Researchers not involved in the study welcomed its findings.

“This is an interesting study that confirms the role of trees in providing critical ecosystem services with clear benefits to human health – supporting climate resilience in the face of warmer summers,” Peninah Murage, of the London School of Hygiene and Tropical Medicine, said.

Peter Crank, of the University of Waterloo in Canada, added: “This study puts a number to how much cooling the city via trees can help our community health,”

“It does a good job of walking through the impacts urban trees would have on human health in London. The authors do a good job of providing tangible benefits and outcomes from trees.”

From 2015 to 2022, London was between about 3.3C warmer than it would have been with much less development.

However, shady trees planted throughout the city can help claw back some of this effect by reducing the average temperature in tree-lined areas by up to 2C, the study found.

To see how greater tree densities were better at reducing heat-related risks to the local population, the researchers collected data from 500 personal weather stations – sets of weather measuring instruments that people installed on their own properties – scattered throughout the city.

They correlated that data with maps of average tree cover, the buildings in the area and their height, and population numbers, before comparing it with official Met Office temperatures for the regions to see how much local tree cover was able to reduce ambient temperatures.

The timeframe for this data included the summer of 2018, the hottest London summer on record, and the intense 2022 heatwave.

The researchers say that, as the climate warms, trees are likely to save even more lives in the future. The study is published in the journal Environmental Research Letters.