Summer’s not over and Europe has already experienced its most severe heatwave on record. Late June brought ferocious temperatures – the UK recorded its hottest ever June reading (36.75°C) and across the continent 10,000 excess deaths were recorded in that period alone. And it’s cities, more than anywhere else, that suffer the most.
The urban heat island effect
Concrete and asphalt soak up and store heat all day. Add in traffic, machinery and air conditioning units pumping out even more warmth, and you get an environment with little vegetation or evaporation to cool things down. This is the ‘urban heat island’ effect – and it makes cities genuinely hazardous places to be during a heatwave.
What can trees do?
Urban trees aren’t just decoration – they’re critical climate infrastructure. Through shade and moisture, they can cool neighbourhoods by up to 8ºC. That’s the difference between a bearable 28ºC and an unbearable 36ºC.
Trees do far more than lower the thermostat, too. They filter air pollution, draw toxins and heavy metals out of the soil, soak up rainwater to ease flooding, and have a well-documented effect on mental wellbeing and community connection. And because tree cover tends to be lowest in lower-income neighbourhoods, planting more trees is as much a matter of climate justice as of temperature control.
A citizen-led blueprint from Berlin
Sometimes the most powerful lever is a law. In Berlin, Ecosia's home city, a citizen initiative turned into exactly that. Over 30,000 residents backed a campaign for a legally binding tree protection and planting law, and last year the Berlin senate approved it unanimously: one million new trees by 2040. The law requires the city to identify its hottest "heat districts" and cool them with trees, green space and shade, targets a tree every 15 metres along city streets, and mandates public reporting on progress. It's a model other cities can copy.
Ecosia's urban tree planting projects
Aside from supporting BaumEntscheid, we've partnered with groups worldwide to bring trees back into cities. In London, we've worked with Greener Together to turn neglected lots into shared green spaces and planted around NHS hospitals. In Los Angeles, we've supported City Plants in restoring an old municipal tree nursery and planting in historically redlined, heat-vulnerable neighbourhoods. And in LA and Chicago, we've partnered with City Plants and Openlands to train local residents to plant, monitor and care for urban trees themselves.
What can you do in your city?
Push your local council for a tree-planting policy, join a community planting day, or simply start asking why your street doesn't have more shade. Berlin shows what's possible when enough people ask the same question.
