A climate essay
Who is heating the planet? and Your seven tonnes dealt in tonnes. This one deals in afternoons. Pick your city and the rest of the page rewrites itself: the city your summer will feel like, the hot days on their way, and the day your record heat stops being a story your family tells.
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The cleanest way to feel a projection is to find the place that already lives it. In 2019, researchers matched the 2050 climate of 520 world cities to the present-day climate of others. Here is what they found for London.
London today: an annual average of 11.1°C, and a typical warmest-month afternoon of 21.0°C.
By 2050, under a moderate emissions path (RCP4.5), the dot slides to an annual average of 13.2°C, with warmest-month afternoons around 26.9°C.
And that spot on the line is not empty. The closest present-day match for London's 2050 climate is Melbourne. Next closest: Istanbul and Barcelona.
One caveat before you book the flight: an analog matches whole-year averages. Extremes move further than means, so your 2050 summer will throw days the analog city rarely sees. The next chart is about those.
A footnote worth keeping: the press release for that study told Londoners to expect Barcelona, and the headline travelled the world. The paper's own tables rank Melbourne first, Istanbul second, Barcelona third. Even good news about bad news gets rounded to the nearest beach.
Each dot below is one day of a typical summer in London. Watch what the count of days over 25°C does as the calendar moves from your parents' summers to your children's.
1981–2000: about 25 days a year over 25°C in London, 2 of them over 28°C.
2001–2020, observed: already 37 days. This is not a projection; it has happened. Across the UK, days over 28°C have more than doubled since the 1961–90 baseline.
The 2050s (a 2°C world, indicative timing 2031–2056): 50 days over 25°C (model range 36–57), and 11 over 28°C.
Tropical nights, when the temperature never drops below 20°C, go from almost unknown to a few every summer. Night heat is the dangerous kind: it is when bodies are supposed to recover.
And if the world reaches 4°C, late this century: 85 days over 25°C, 30 over 28°C. That is not a hot summer; that is a different calendar.
London's hottest day on record: 40.2°C, 19 July 2022, at Heathrow & St James's Park.
Against it, today's typical warmest-month afternoon: 21.0°C. The record is an outlier, the kind of day that gets its own name in the family.
By 2050 the typical warmest afternoon moves to about 26.9°C (RCP4.5). The gap between "ordinary hot" and "all-time record" halves, which is exactly how records stop being records.
The UK's own all-time mark, 40.3°C at Coningsby in July 2022, was once considered impossible here. Met Office projections have UK hot spells going from one every five years to about four a year by the 2070s.
This one is UK-wide rather than city-by-city, because that is how the Met Office publishes it. It is the gentlest chart on this page, and in the long run maybe the biggest.
The ring is a year. In the 1961–1990 climate, England's growing season, the stretch warm enough for things to grow, ran about 251 days.
By 2006–2015 it averaged 280 days: twenty-nine days longer, a whole extra month of growth, taken from winter's end and autumn's start.
The newer measure tells the same story: 21% more growing degree days in 2015–2024 than the 1961–90 baseline. Gardens notice before governments do: earlier blossom, later frosts, lawns that never quite stop.
Warmer summers do not just mean sun. For southern England, the UKCP18 projections move the rain itself.
Summers get drier: by the 2050s, southern England's summer rainfall shifts by −12% to −44% across the scenario range.
Winters get wetter: +9% to +28%. The water arrives when reservoirs are full and gardens are dormant, and goes missing when everything is thirsty.
Summer afternoons also warm by +1.9 to +3.9°C on average. Drier ground, hotter air: the same combination behind the fire-and-hosepipe summers the UK has started to rehearse.
Your hand on the dial turns the question the other way: the levers that decide whether your city's calendar stops at the 2°C column or keeps going.