Hotter for Some

Chapter 1

Two summers in one city

Huttenstraße in Moabit, a weekday in July. The pavement is still warm at midnight, the courtyards of the old tenements hold the day's heat like ovens, and the few street trees cast thin shade. Some fourteen kilometres to the south-west, in Nikolassee, the same sun falls on gardens, lakes and the edge of the Grunewald forest. Both places are Berlin. They do not have the same summer.

Climatologists call this the urban heat island. Asphalt, stone and roofs soak up sunlight during the day and release it at night; buildings block the wind; there is little soil or vegetation to cool the air by evaporation. For air temperature, the effect is strongest at night. In 2024, the German Weather Service station at Alexanderplatz recorded 22 tropical nights, nights in which the temperature did not fall below 20 °C. The station in leafy Dahlem recorded two (Abgeordnetenhaus Berlin, 2025).

Research from many cities shows that this heat is not shared out at random. In a study of 25 cities around the world, poorer neighbourhoods were exposed to more urban heat in 72 per cent of cases (Chakraborty et al., 2019). Across 683 European cities, urban form, from building density to the amount of green space, explains around 70 per cent of how unequally surface heat is distributed (Mashhoodi & Muñoz Unceta, 2024). And a study of 14 European metropolitan areas, Berlin among them, found that lower-income residents, tenants and immigrants everywhere receive less cooling from urban greenery than homeowners and the well-off (Rocha et al., 2024).

This issue asks what that looks like in Berlin, neighbourhood by neighbourhood. Who gets the shade, and who is left with the heat?

Chapter 2

Who a heatwave kills

Heat stress is the leading climate-related cause of premature death in Europe (Rocha et al., 2024). In the summer of 2022 alone, an estimated 61,672 people in 35 European countries died from heat, 8,173 of them in Germany; relative to population, women were hit 56 per cent harder than men (Ballester et al., 2023). The Robert Koch Institute estimates about 3,100 heat-related deaths in Germany in 2023 and 2,800 in 2024 (an der Heiden, 2025). In Berlin, about five per cent of all deaths between 2001 and 2010 could be statistically linked to high temperatures, most of them among people aged 65 and over (Scherer et al., 2014).

Heat rarely appears on a death certificate. It kills by pushing an already weak heart, lung or kidney past its limit, and it kills most reliably at night, when the body cannot recover from the day. That is why the people at greatest risk are those who are old, ill, alone, and stuck indoors in a flat that never cools down. Almost 240,000 Berliners are 80 or older (Ärztekammer Berlin, 2026).

Money decides how well people can escape. A survey of Berlin households found that 37 per cent of those with a monthly income of at least €5,000 had air conditioning, and that residents of dense, closed blocks of flats perceived the most heat stress (Iqbal et al., 2025). A shaded garden, a top-floor flat with insulation or without, a weekend house in Brandenburg, the option to work from somewhere cooler: each of these is a way to buy distance from the heat. Those who cannot afford them stay where it is hottest.

Chapter 3

The longest nights

Daytime heat is only half the story. What harms health most is when the night brings no relief. For this, the satellite data are not enough, so I used the city's own climate model. It shows how warm the air is at 4 a.m. on a still summer night, block by block. Across the planning areas the values range from 16.1 °C on the rural fringe to 19.3 °C in the densest inner-city blocks.

Here the pattern shifts. At night, the main divide is between the centre and the edge: the large housing estates of Marzahn or Spandau, with wide open spaces between their towers, cool down; the closed courtyards of Wedding, Kreuzberg and Neukölln do not. On their own, unemployment and benefit receipt say little about night-time heat once location is taken into account. One group, however, stands out: older people living in poverty.

The social monitoring records the share of residents above the statutory retirement age who depend on basic income support in old age (Grundsicherung im Alter). Where this old-age poverty is highest, nights are hottest. Of the 134 planning areas in the top quarter for old-age poverty, 68, or half, are also in the top quarter for night-time temperature, twice as many as chance would predict. 546,000 people live in these 68 areas, most of them in Friedrichshain-Kreuzberg, northern Neukölln and Mitte (including Moabit and Wedding), with smaller clusters in Charlottenburg and Schöneberg (Figure 4). The link holds even at the same distance from the centre.

The two neighbourhoods from the beginning sit at opposite ends of every one of these measures. In the Huttenkiez in Moabit, 24 per cent of residents receive welfare benefits (not counting the registered unemployed), and 28 per cent of pensioners depend on basic income support. Its built-up blocks are 3.6 °C hotter than the city median at midday, its vegetation index is 0.18, and at 19.3 °C its modelled night is the warmest of all 536 planning areas. In Nikolassee, the figures are 4 and 3 per cent. Its blocks are 3.9 °C cooler than the median, its vegetation index is 0.68, and its night 17.3 °C.

A difference of two degrees at night sounds small. For an 85-year-old woman with heart failure on the fourth floor of a building without insulation, it can decide whether her body gets the few hours of recovery it needs.

Chapter 4

What the map does not show

The data also complicate the simplest version of this story. Berlin's poorest neighbourhoods are not its very hottest: areas with a very low social status are, on average, no hotter than areas with a medium one. The very hottest surfaces lie in mixed areas full of factories, warehouses and large flat roofs, such as Marienfelde or Borsigwalde, whose residents mostly have a medium status. Prenzlauer Berg, one of the most sought-after Altbau districts in the city, has some of its warmest nights. And some of the poorest areas are relatively cool: in Marzahn West, where almost one in five residents receives welfare benefits, the prefabricated blocks stand between generous green spaces, and the modelled night is two degrees cooler than in the Huttenkiez.

So the sharpest line in Berlin does not run between poor and middle-class neighbourhoods. It runs between the best-off fifth of the city and everyone else. Divided by benefit receipt into five equal groups of planning areas, the fifth with the fewest people on benefits is 0.7 °C cooler than the median; the other four are between 0.6 and 1.0 °C hotter, with the poorer two fifths slightly hotter than the middle. Cool surfaces at midday are largely a privilege of the villa suburbs.

That fits what other researchers have found. In Berlin, lower-income groups are concentrated in central areas with little green cooling, and Berlin is one of four of the 14 European metropolitan areas studied where low income and missing green cooling overlap most strongly in space (Rocha et al., 2024). Researchers who surveyed Berlin households found only a weak direct link between income and perceived heat, but a clearer one between perceived heat and dense building types (Iqbal et al., 2025). Heat follows the built form of the city, and the built form follows a long history of who could afford to live where.

What the map cannot show is perhaps the most important part: who can protect themselves indoors. A wealthy household in a hot Kreuzberg Altbau may own air conditioning, travel in August or sleep in the country. A pensioner on basic income support in Wedding usually cannot. Exposure is shared more widely than vulnerability.

Chapter 5

Shade as policy

Berlin has begun to respond. In August 2025 the Senate health department launched a heat protection portal with a map of cool places where people can escape the heat (SenWGP, 2025). A citywide heat action plan followed in November 2025 (Senatskanzlei Berlin, 2025). And after pressure from the citizens' initiative BaumEntscheid, the House of Representatives passed the BäumePlus law in November 2025, which for the first time sets legally binding targets for planting street trees in Berlin for climate adaptation. It foresees around 560,000 new street and park trees by 2040, for a total of one million, and about 170 "heat districts" in heavily sealed areas where streets and courtyards are to be unsealed and greened (Entwicklungsstadt, 2025a). Shortly afterwards, however, the governing coalition committed only about one billion euros up to 2040, against estimated costs of up to 3.2 billion (Entwicklungsstadt, 2025b).

The analysis here suggests two things for how that money is spent. First, heat and social data should be read together. A plan guided only by temperature will spend as much in well-off Prenzlauer Berg as in Moabit; a plan guided only by poverty will miss that the large estates on the edge are already relatively green. Where both overlap, in Figure 4, is where trees, shade and cool rooms protect the most vulnerable people.

Second, greening must not price out the people it is meant to protect. A study of 28 cities in Europe and North America found that in 17 of them, new parks and greenery in the 1990s and 2000s were followed by gentrification (Anguelovski et al., 2022). If Berlin's new trees end up raising rents in the Huttenkiez, the heat will simply move with the people who can no longer afford to stay.