A shade audit puts nine in ten buildings in London, Paris and Madrid below the cooling threshold

Begin with the geometry, because that is what the 60 metre rule is really asking for. The area within 60 metres of a dwelling is about 11,300 square metres (pi times 60 squared), so 30 to 40 percent shade cover inside that circle works out at roughly 3,400 to 4,500 square metres of canopy per address ^[17]. Those circles overlap between neighbours, so the requirement is not additive down a terrace, but it is closer to a small orchard per block than to a street tree per door ^[17]. That is how London can hold around 8 million trees ^[6] and still have more than 90% of its buildings inadequately shaded ^[1]: the total is large, but it sits in the wrong places. Fewer than one building in ten in the three worst-scoring capitals clears the bar ^[18].

This measures geometry, not epidemiology. The 30 to 40 percent figure comes from earlier work on preventing heat island formation ^[4], and the step from shade cover to deaths avoided is an inference from temperature differences, not an outcome tracked in these cities ^[3]. The Create Streets Foundation contrast, 55C on exposed London paving during a heat wave against 25 to 30C in shade metres away ^[8], is a surface reading at one site on one day, a 25 to 30 degree gap that tells you what asphalt does under direct sun ^[19] rather than what happens in any resident's bedroom at 2am.

Treat the headline cooling numbers with the same care. Tree shade has been shown to cut the heat absorbed by pedestrians by up to 18C ^[9], a measure of radiant load on a body rather than a drop in air temperature. Air temperature gains a few extra degrees from evaporative cooling, and the source is explicit that this holds only while trees can still reach water ^[12]. That condition does real work in the scenario the research is aimed at: the same London summer that filled wards with heat casualties also dried soils enough to crack homes through subsidence ^[14].

There is a denominator problem worth flagging before anyone builds a league table. The London, Paris and Madrid results are reported as shares of buildings; Hamburg's 56% and Barcelona's 70% are reported as shares of residents without adequate protection ^[20][2]. A residents-based count weights an apartment block by its occupancy, a buildings-based count does not, so Hamburg's implied 44% protected ^[21] and London's sub-10% are not yet strictly comparable. The ranking is ordinal at best until the work is published in one unit.

My view, with its conditions attached: canopy percentage across a whole city measures something different from the quantity that actually governs exposure, which is the share of dwellings above the threshold within 60 metres. A planting programme can raise the first while leaving the second flat, and the standard being proposed here, three trees in view and a park within a 300 metre walk ^[5], is the version that would catch that. It also carries an obligation the totals hide, which is choosing species that can survive the temperatures they are being planted to blunt ^[22].