{"id":"koppen-climate-classification-limits-84299","slug":"koppen-climate-classification-limits-84299","title":"Köppen's 30 Boxes vs. a Changing Planet","description":"Every square kilometre has a climate nothing else quite shares, yet climatologists compress that vast list into a handful of archetypes. This episode digs into the two families of climate classification — genetic methods that sort by causes, and empiric methods like Köppen-Geiger that sort by effects — and asks whether the archetype is a real instrument or a convenient fiction. From Trewartha's fix for Köppen's fat mid-latitude group to Thornthwaite's soil water budget and the air-mass schemes that abandon averages entirely, we trace what each system throws away. Then we point the map at a changing climate: roughly 5% of global land has already moved to a different major Köppen class since 1901–1930, Hungary sits at 81% shifted, and the classification is structurally blind exactly where warming bites hardest. A taxonomy episode about what a class can and cannot tell you.","excerpt":"Köppen squeezes the planet into 30 boxes — and the hottest places can't change class, even as they heat. What the map hides.","pubDate":"2026-10-17T11:16:31.332Z","tags":["taxonomy","atmospheric-science","environmental-health"],"heroImage":"https://files.myweirdprompts.com/covers/koppen-climate-classification-limits-84299.png","podcastAudioUrl":"https://episodes.myweirdprompts.com/audio/koppen-climate-classification-limits-84299.m4a","podcastDuration":"20:11","episodeNumber":6053,"transcript":"Corn: The atlas runs out of colours somewhere around the Caspian Sea, and you stop looking. One page, maybe two, the whole planet reduced to bands. That's the thing I keep chewing on.\n\nHerman: Every square kilometre has a climate nothing else quite shares, and the map hands you eight colours and a legend.\n\nCorn: That's the tension Daniel's poking at. He says every place has a slightly unique climate, the interaction of local landscape and global forces, and then climatologists take that vast list and stratify it into a few archetypes. He wants to know what the basic stratification actually is, and whether the compressing is a worthwhile exercise for people studying climate change and drafting policy.\n\nHerman: Worthwhile how, though. That's the interesting half of the question.\n\nCorn: Whether the archetype is a real instrument or a convenient fiction. And whether you can point it at a changing climate and then hand the result to a regulator.\n\nHerman: The bit that gets me is that both halves of Daniel's prompt are testable. What's the map, and does it hold up under use.\n\nCorn: Before we argue about whether the archetypes are worth having, somebody should say what they actually are.\n\nHerman: Give me one clean sentence first, because the whole thing hangs on a distinction most people never hear. Climate classification splits into two families. Genetic methods sort places by causes. Air-mass frequency, where a place sits within the passing weather systems.\n\nCorn: And the other family?\n\nHerman: Empiric. You sort by effects. What grows there, how much water leaves the soil, which biome it resembles. Köppen is the second kind, and that's not a small footnote. It's the reason the system can serve as an ecological indicator later and the reason it has the blind spot it has.\n\nCorn: The map in the atlas is a compression algorithm. It throws away nearly everything about a place to keep the one thing that lets you compare Hungary to Canada.\n\nHerman: Roughly. The main characters are Köppen-Geiger, that's the dominant one, then Trewartha, Thornthwaite, Holdridge, and the air-mass schemes that try to classify by the weather itself rather than the average.\n\nCorn: Two colours on a page, one argument underneath about what a class can even tell you.\n\nHerman: Let's start with the system everyone has actually seen, the one on the wall of a geography classroom.\n\nCorn: Köppen needs a person attached to it, because the man's job explains the design.\n\nHerman: He was a botanist. That's the lot. His five major groups were drawn to line up with the major ecosystem types, so regions landing in the same class share broadly similar vegetation. He published in 1884, revised in 1918 and 1936, Geiger came in during the fifties and early sixties and left his name on it.\n\nCorn: Five groups, A tropical, B dry, C temperate, D continental, E polar, and thirty sub-classes underneath.\n\nHerman: The sub-classes are just letters stacked. Af is tropical rainforest, Cfb is oceanic with a warm summer, Dwb is semi-monsoonal continental with a warm summer. Two letters do a lot of work when you've only got thirty boxes for a planet.\n\nCorn: Thirty boxes, and one of them is holding both London and New Orleans.\n\nHerman: That's the flaw, and it's the reason Trewartha exists. Under plain Köppen the temperate C group is enormous. London and New York sit in group C alongside Brisbane and New Orleans, which is a category that's stopped discriminating.\n\nCorn: Coastal drizzle and subtropical swamp in one column.\n\nHerman: Trewartha's fix was to split the mid-latitudes by how long the warm season lasts. Subtropical is eight or more months at ten degrees or above, temperate is four to seven months, boreal is one to three. Same idea, finer comb. Also, under Köppen, Washington and Oregon share zone Csb with parts of Southern California, which tells a farmer almost nothing useful.\n\nCorn: So Trewartha patches the group that got too fat. What does Thornthwaite patch?\n\nHerman: Water. Thornthwaite is 1948, and instead of asking what grows, it tracks the soil water budget through evapotranspiration. Humidity and aridity indices running from hyperhumid down to arid, thermal classes on top. Microthermal, mesothermal, megathermal.\n\nCorn: Under that index, a third of the land is arid or semi-arid. Which is a more honest number than Köppen gives you.\n\nHerman: Holdridge is the elegant one. Nineteen forty-seven, uses biotemperature, precipitation, latitude and altitude in a triangular chart. You can read a life zone off two axes and a position.\n\nCorn: And the air-mass schemes give up on averages entirely.\n\nHerman: The Bergeron family, and the Spatial Synoptic Classification as the modern version. Six categories. Dry Polar, Dry Moderate, Dry Tropical, Moist Polar, Moist Moderate, Moist Tropical. You classify a place by which air masses reach it and how often.\n\nCorn: That's the genetic family. Sorting by the cause rather than the symptom.\n\nHerman: Right, and it fixes the thing that bothers me about Köppen, which is that a monthly average is a number nobody experiences. You don't live in a July mean, you live in the days.\n\nCorn: What turns a latitude band into a specific place, though? That's the half of Daniel's prompt that's landscape rather than taxonomy.\n\nHerman: The criteria in Köppen are just monthly temperature and monthly precipitation. Nothing else. But the modern one-kilometre maps aren't built from station averages alone. They're built from climatologies that have been corrected for topography. Elevation, slope, the shape of the ground.\n\nCorn: Which is how a one-kilometre grid catches a mountain valley a coarse map would smear across the whole region.\n\nHerman: It also catches small islands. There are island climates that a two-hundred-kilometre grid simply erases, because the island falls between the cells.\n\nCorn: Rain shadow is the clean example of a landscape manufacturing a climate out of a region's average.\n\nHerman: Mountains block the path of moisture and precipitation. The windward side wrings the water out of the air, the lee side gets the left-over air, dry and warmed. That's how a good number of the world's deserts are made. They're not a latitude phenomenon, they're a rock phenomenon.\n\nCorn: The global forces give you the latitude band. The rock decides what kind of place it turns into.\n\nHerman: And this is where the honest weakness has to be said out loud, because it's structural, not a bug they'll patch. Classification puts a boundary between zones, and nature has a gradual transition instead. A line on a map is a decision, not a discovery.\n\nCorn: Somebody drew it, and a mountain slope quietly ignores it.\n\nHerman: There's a second-order version of that, too. Biome change doesn't have to follow class change. A place can move into a different Köppen class and its vegetation doesn't shift with it, because soil, CO2 fertilisation, fire, invasive species and land use are all sitting on top of the climate as separate variables.\n\nCorn: The classification is a description of a climate. It's not a prophecy about a plant.\n\nHerman: The map in the atlas isn't one thing either. It's the same answer, but it's not a fixed reference. Those one-kilometre maps get rebuilt for each thirty-year period, from corrected climatologies. It's not the plate in the textbook. It's a file that gets re-made.\n\nCorn: Held still long enough to print and not one day longer.\n\nLarry: Are you tired of climates that change every thirty years without asking permission? Introducing Climate Tier, the only monthly subscription box for people who want their local weather delivered. Tier One, Temperate Curious. You receive one leaf, seasonally appropriate, cancellation fee applies. Tier Two, Arid Enthusiast. A jar of dust, forty-page manual, no refunds ever. Tier Three, Continental Premium. Nineteen consecutive days of drizzle, delivered by courier. Cancel any time, meaning never, and we keep charging your card. Climate Tier. The climate you own, every month.\n\nHerman: Temperate Curious. A leaf. Climate is a thirty-year average, not a leaf.\n\nCorn: Let it go, Herman.\n\nHerman: I cannot let it go, it said the climate changes every thirty years. The thirty years is the window you measure in, not the rate anything happens at.\n\nCorn: The ad's wrong and the leaf is a leaf. Move.\n\nHerman: Point taken.\n\nCorn: The taxonomy's done. What happens when you point it at a changing climate and hand the result to a regulator?\n\nHerman: This is where the archetype earns its keep, and the numbers are the argument. Between the period 1901 to 1930 and the period 1991 to 2020, about five percent of global land outside Antarctica moved to a different major Köppen class.\n\nCorn: Five percent doesn't sound like much until you put a landmass next to it.\n\nHerman: Two point six million square kilometres go from polar to cold under the middle scenario, which is roughly Argentina. Two point four million cold to temperate. One point one million cold to arid. Two point eight million temperate to tropical, that's the biggest single flow.\n\nCorn: So the archetype is what lets somebody say a sentence like that at all.\n\nHerman: Without the class you'd be talking about temperature deltas per pixel, which nobody can hold in their head, and no minister can act on. The class is the unit that makes the change sayable.\n\nCorn: And the projections to the end of the century?\n\nHerman: Five percent of land changes major class under the low scenario, eight under the middle, thirteen under the high. Under the middle one, land suitable for tropical vegetation grows eight percent, arid grows four. Temperate loses three, cold loses two, and polar loses a third.\n\nCorn: A third of the polar class is one long, slow eviction.\n\nHerman: Now the flaw, because there is one and it's beautiful. Köppen put deserts and the tropics near the top of the temperature scale. Which means the hottest places in the classification cannot change class. There's nowhere hotter to go. They only get hotter inside the box they already occupy.\n\nCorn: So the tool that tells you how much land will change class is structurally blind in the places changing hardest.\n\nHerman: The instrument shapes what change is visible. That's not a small philosophical point, that's a reporting gap at exactly the latitude where it hurts. And there's a second one. The maps are validated against more than a hundred and seventy thousand weather stations, and they hit about seventy-nine percent to eighty-six percent on the thirty sub-classes.\n\nCorn: Accuracy figures that high on thirty boxes is respectable. Where's the problem?\n\nHerman: The accuracy for the recent period is lower than for the earliest one. Seventy-nine percent against eighty-six. The authors put it down to the climate moving under the labels. A single class is harder to pin a place to when the place is halfway between two.\n\nCorn: The archetypes are getting blurrier exactly as we need them.\n\nHerman: One of the explainer pieces around that dataset runs a line I keep thinking about. These maps were made for a climate that doesn't exist any more.\n\nCorn: Give me a country, because a percentage of global land doesn't scare anybody.\n\nHerman: Hungary. Eighty-one percent of the country has already shifted into a different, more temperate zone. The most of any nation in the dataset.\n\nCorn: Eighty-one percent of a country whose building regulations were written against the old number.\n\nHerman: Canada and Russia are at twenty-four percent already shifted, with another thirty-nine to forty percent to follow by the end of the century. Eastern Europe is the hotspot. Cold-winter continental becoming temperate with hot summers. South Africa, Eswatini and Lesotho, twenty-eight percent shifted with another forty-four to come. Australia, fourteen and thirteen.\n\nCorn: Hungary's the case that matters for policy, because a building code is a promise that a zone is stable.\n\nHerman: Which is exactly what the building literature means by a climate zone. A region where the climatic variables vary little, so you can apply uniform mandatory values across the whole area without arguing about every site. The United States assigns every county a zone through the energy code and the Department of Energy's programme, and that zone sets mandatory envelope requirements. Insulation, glazing, air tightness.\n\nCorn: So the entire justification of the zoning is that the variation inside it is small.\n\nHerman: And Hungary is the country where it stopped being small. The regulatory map is now describing a climate the country doesn't have. Whether anyone has redrawn it is a separate question, and I don't have a clean answer to that.\n\nCorn: Agriculture does it too. Brazil's zoning,\n\nHerman: ZARC, implemented in ninety-six. It delineates municipalities and planting windows by agroclimatic risk, and all of it sits underneath crop insurance and rural credit. If you plant outside your window you lose the cover.\n\nCorn: Which is a much sharper instrument than a building code, because it fires the same season.\n\nHerman: There's a fork in the road here that Daniel's prompt is really pointing at, and I don't think most people see it. There are two different kinds of stratification in play, and they answer different questions.\n\nCorn: Go on.\n\nHerman: Köppen stratifies by what the climate is like. Bioclimatic type. The IPCC doesn't use Köppen for its policy regions at all. It uses its own reference regions, forty-six land, fifteen ocean, three hybrid, drawn as shapes on the globe. That stratifies by where a place is. So one system tells you what a place can grow. The other tells you whose projections to go read.\n\nCorn: The same word, region, doing two unrelated jobs.\n\nHerman: And policy needs both. The building code needs the type, because the type tells you what the envelope has to do. The IPCC needs the place, because a projection is only meaningful over a defined footprint. Nobody has to choose between them and it'd be a mistake to think one replaced the other.\n\nCorn: There's a last layer underneath all of it, which is that every number we've said comes out of a model.\n\nHerman: Sixty-seven models get evaluated for this work. Eighteen of them have all the sensitivity metrics inside the likely ranges. The rest get dropped, and forty-two are retained overall.\n\nCorn: Which is a polite way of saying the ensemble is not a democracy.\n\nHerman: The line in the paper is that using the full set uncritically can mislead you, and shouldn't guide real decisions. So the archetype is only as good as the projections being poured into it. A clean instrument fed a bad ensemble gives you a confident wrong map.\n\nCorn: Sixteen years of my life went into believing the atlas was a reference. That's not the paper's fault.\n\nHilbert: They were right, mostly.\n\nCorn: Mostly.\n\nHilbert: The compression works. I'd go further than either of you, though. The most consequential climate classification in an ordinary person's life isn't Köppen. It's the number on the back of a seed packet.\n\nHerman: The hardiness zone.\n\nHilbert: Zone six. That's what it said when I bought the place, and it says zone seven now, on the newer packets, for the same garden. Nobody surveyed the garden. The number came down from a county extension office that reclassifies in bulk, and the packet printer absorbed the change a year or two later and nobody told the people planting.\n\nCorn: And you checked.\n\nHilbert: I checked. I rang the extension office in the spring and asked which map they were using, and the woman said she'd have to get back to me. That was four years ago. She hasn't got back to me and I haven't stopped asking.\n\nHerman: Four years of phone calls.\n\nHilbert: Two calls a year, mostly, plus the letters. I wrote to the state office twice. Second letter I enclosed a photocopy of the old packet and the new packet side by side, circled the number, and wrote underneath, which one is true. No reply. I keep the copies in a shoebox, sorted by year, and I've got a shoebox and a half.\n\nCorn: A shoebox and a half of seed packets.\n\nHilbert: This level's a bit hot on the second one, Herman, bring it down a touch on the next pass.\n\nHerman: Noted.\n\nHilbert: The part I object to is that a grower picks a variety by that number. You buy a tree that's rated for zone six and the winter takes it, you've lost five years before your first crop. The number decides what gets planted. Nobody audits it. The whole of Köppen gets its thirty-year revision and its hundred and seventy thousand weather stations, and the packet gets a number that was assigned to a county before the grower was born.\n\nHerman: The reclassification does come from the same kind of data, just at a coarser scale, county by county, lowest winter temperature averaged over a window. It's the same instrument, badly lagged.\n\nCorn: Which is why the letters.\n\nHilbert: I planted a zone seven pear anyway. It came through four winters and then died in the fifth, and I know exactly which winter it was.\n\nCorn: How much did the pear cost?\n\nHilbert: Forty-one dollars, bare root, postage included. I've still got the invoice.\n\nCorn: I'll take the pear over the whole atlas.\n\nHerman: A seed packet is a policy document that fits in a pocket. The zone is a mandatory value applied uniformly across an area, same definition as the building code, except it's enforced by the plant dying.\n\nCorn: And the woman on the phone is the regulator.\n\nHerman: Which sets up the question we can't answer on air, which is what happens when the map gets coarser because the ground underneath it moved.\n\nCorn: If the instrument blurs as the climate shifts, do we build a sharper instrument or just accept a map that lies by the decade?\n\nHerman: And the structural point sits underneath it. The hottest zones can't change class, they only intensify, so the map will always under-report change in the places changing hardest. An instrument that under-reads its own loudest signal.\n\nCorn: Which is the thing to leave people with. Also, Hilbert's pear died in a winter nobody at the extension office ever asked about.\n\nHerman: Producing today by Hilbert Flumingtop, who is owed a phone call from a county office. If you want more of this, try episode four, If Your Voice Ages, Does Your Fine-Tune Become Useless; episode twenty, Architectural AI; and episode eleven, How Does Fine Tuning Work Anyway. This has been My Weird Prompts.\n\nCorn: Reviews help more than the leaf does. See you soon.","showNotes":"Climate classification splits into two families. Genetic methods sort places by causes — air-mass frequency, where a place sits within passing weather systems. Empiric methods sort by effects — what grows there, how much water leaves the soil. Köppen-Geiger is the second kind, and that's not a footnote: it's why the system works as an ecological indicator and why it has the blind spot it has. Köppen, a botanist, drew his five major groups to line up with major ecosystem types, published in 1884 and revised through 1936, with Geiger joining in the fifties. Thirty sub-classes, letters stacked — Af, Cfb, Dwb — and one of those boxes holds both London and New Orleans. Trewartha's fix was to split the mid-latitudes by how long the warm season lasts. Thornthwaite tracks the soil water budget through evapotranspiration instead, and under its index a third of the land is arid or semi-arid. Holdridge reads a life zone off a triangular chart of biotemperature, precipitation, latitude and altitude. The air-mass schemes give up on averages entirely, classifying by which air masses reach a place and how often.\n\nWhat turns a latitude band into a specific place is landscape. Rain shadow is the clean example — mountains wring moisture out of the windward air, and the lee side gets dry, warmed leftovers. A good number of the world's deserts are a rock phenomenon, not a latitude phenomenon. And the honest structural weakness: classification puts a boundary where nature has a gradual transition. A line on a map is a decision, not a discovery.\n\nPointed at a changing climate, the archetype earns its keep. Between 1901–1930 and 1991–2020, about 5% of global land outside Antarctica moved to a different major Köppen class — 2.8 million square kilometres temperate to tropical, 2.6 million polar to cold. Projections run 5% under the low scenario, 8% middle, 13% high. But Köppen put deserts and the tropics near the top of the temperature scale, so the hottest places cannot change class — they only get hotter inside the box they already occupy. The instrument is blind exactly where change bites hardest. And accuracy on the 30 sub-classes is lower for the recent period (79%) than the earliest (86%), because the climate is moving under the labels. Hungary: 81% of the country already shifted into a more temperate zone, the most of any nation — a building code written against a number that no longer holds.","promptSanitized":"Every place on the planet has a slightly unique climate, the interaction of local landscape, global forces, climatic forces, but climatologists have stratified this huge list of global climates into a few archetypes, as it were. Let's look at the basic stratification that's used and how doing this is actually a worthwhile exercise for those looking at climate change and formulating policy.","transcriptUrl":"https://episodes.myweirdprompts.com/transcripts/koppen-climate-classification-limits-84299.md","url":"https://myweirdprompts.com/episode/koppen-climate-classification-limits-84299/","_links":{"self":"https://myweirdprompts.com/api/episodes/koppen-climate-classification-limits-84299.json","html":"https://myweirdprompts.com/episode/koppen-climate-classification-limits-84299/","audio":"https://episodes.myweirdprompts.com/audio/koppen-climate-classification-limits-84299.m4a"}}