When the extreme heat hits Ireland, we’ll be grateful to the trees

Ella McSweeney: Younger kids, older people, outdoor workers, pregnant women are all disproportionately vulnerable to heat stress and mortality

Trees are our cheapest and most effective bulwark against extreme heat. Photograph: iStock

I’m lucky to have a bit of garden, and about five years ago, I decided to transform a semi-shaded triangular patch of grass – about the size of three car spaces – into a miniature wood. I crammed about 45 native trees together and, competing for sunlight, they’ve grown well. Birds bounce from tree to tree, picking off moths and other insects along the way, and the soil has improved.

What surprises me is the microclimate within this space. Standing in the middle of the patch, the air feels cleaner, and on warm days, there’s a noticeably moist coolness to the place. It makes sense, as trees are nature’s mist cooling systems; a network of tubes pulls water from the roots in the soil up through the stems and the leaves, where the water evaporates into the air, cooling the tree and the surrounding environment along the way.

But unlike human-made mist cooling systems, trees do this for free. A large oak can transpire up to 400 litres of water a day, and its broad canopy acts as an umbrella, reducing the amount of sunlight that hits the ground. In a study of 108 US cities, the difference between the hottest and the coolest neighbourhoods was as significant as 10 degrees, much of which was attributed to the distribution of trees.

We need to start thinking about how we’ll keep cool in the future. We’ve just emerged from the warmest May on record, which many of us probably barely noticed because it was influenced by elevated overnight temperatures. But we’re rapidly turning up the heat, prompting the UN’s secretary- general António Guterres to plead for action. “Our planet is trying to tell us something. But we don’t seem to be listening,” he said last month. “Now is the time to mobilise, act and deliver.”


Last month, hundreds of the world’s leading climate scientists predicted a “semi-dystopian” future driven by heatwaves, floods and storms, with “major societal disruption” within the next five years caused by the 80 per cent likelihood that we’ll exceed 1.5 degrees warming within that period. We’ve failed to cut emissions quickly enough to reach our 2030 target in Ireland, which leaves a grievous future for our young people to face.

Nature is never without drama and noticing it is an active choiceOpens in new window ]

So, we must consider worst-case scenarios and plan accordingly and as quickly as possible. The frequency of heat extremes and heatwaves in Europe has grown since 2000. Two-thirds of people in Ireland live in urban areas in Dublin, where the population continues to grow, and exposure to heat hazards is projected to increase considerably over the next few decades.

Urban areas have surfaces that absorb heat, such as concrete and asphalt, and not enough green spaces to cool things down. During hot summer days, this can mean that areas warm up like a frying pan. This “heat island” effect in cities will increase with high-density housing and development expansion.

Some people are more heat-vulnerable than others. Younger kids, older people, outdoor workers, the socio-economically disadvantaged, pregnant women and the chronically ill are all disproportionately vulnerable to heat stress and mortality.

In April, Cork City Council adopted a tree strategy that could see the city’s tree cover double to 30 per cent over the next few years. New tree planting will focus on neighbourhoods with the lowest canopy cover, which include areas listed as disadvantaged in Pobal’s Deprivation Index, such as Fairhill and Knocknaheeny. The aim is to work with the community to plant trees and green the area.

Trees in urban places offer more than protection from a heating city. The evidence shows that living in a green area is linked to lower rates of diabetes, high blood pressure and heart attacks in adults. A 2015 study on urban centres in Canada showed that having just a few more trees – about 11 or so – in a city neighbourhood decreased heart-related conditions, similar to increasing annual income by $20,000 (€13,500). More trees improve mood, reduce stress in pregnant women and help people feel more connected to each other.

None of this will be news to the people living in the Larchville/Lisduggan estates in Waterford city, who have been regenerating their area with trees for years. A team of local volunteers has planted apple and plum trees, greened up their urban spaces with flowers for butterflies, and established vegetables in raised beds. They’ve acted to benefit nature and leave their community, which is classified as extremely disadvantaged, in a better state than before.

The Nature Restoration Law, which has the support of chief executives from transnational companies such as Danone, Nestle and Unilever, includes a plan for greening our urban spaces. If it survives Europe’s swing to the right in last week’s elections and becomes law, it will mean that as our urban spaces grow to meet housing demands, our green spaces won’t be lost but will increase by 3 per cent instead. By 2050, we could have a minimum of 10 per cent tree canopy in all our cities, towns and suburbs.

Trees are our cheapest and most effective bulwark against extreme heat. It’s hard to imagine a future when we’re sweltering from severe summer heatwaves – they’re still rare here, but scientists are clear that this is changing. When the heat hits, we’ll be grateful to the trees and all they freely give us as we stand under their canopies and soak up the cool shade.