— Overview
The essay starts from a hypothesis, not from a season that has already arrived. What if, from July to September, the daily average in Korea sat near 40°C, and the night did not fall below 30°C? The writer is careful to say that this would go well beyond what has been observed. Korea did have spells, in 2018 and in 2022, when the daily average stayed above 30°C. Under the harsher hypothesis, the burden would not stop with weaker photosynthesis by day.
A night that stays hot would raise the plant’s respiration, so that carbohydrates made in daylight are spent again before they can be stored as starch, and ripening would fall off sharply. After the monsoon, as daylight shortens, heat at heading and at grain filling can land together. Heat also checks pollen germination at flowering and can distort a panicle as it forms, raising sterility. In 2018, in coastal paddies of Gyeongnam and Jeonnam, fields that headed while the night stayed above 27°C saw sterility rise by an average of more than 20 percent.
Night-heat experiments reported from Kyushu and from parts of southern China found that when the night exceeded 28°C, the share of perfect grains in brown rice fell by 15 to 20 percent, protein rose, and the eating quality declined. Those results stay in the accounts as given. Photosensitive varieties, which take a changing day length as their cue to flower, may read that cue less clearly in lasting heat: heading can come late or unevenly, and the farmer’s harvest plan becomes harder.
Temperature-sensitive varieties, often grown in inland or upland districts that rely on a cool night, can lose that advantage; roots respire more, take up less, and the top of the plant weakens. Short-season types, less tied to day length or to temperature cues, keep a more predictable heading date, so a farmer may still shift sowing or cut earlier, but grain filling can be too short and unripe grain more common. An ordinary Korean summer, the essay says, sits around 25 to 28°C; above a threshold of about 35°C, enzymes such as Rubisco lose activity quickly.
Short-term answers include irrigation with cool water held at 22 to 24°C, shade nets or trees at the edge of a field, less nitrogen before heading, and, where the heat is not months long, a shift in sowing. The Rural Development Administration’s heat-tolerant lines Nampyeong and Jinsu are named as work already in use. Drawing on FAOSTAT and USDA figures, the essay puts world paddy output at about 700 million tons in 2013 and close to 800 million tons in 2023, with Asia holding about 90 percent of that harvest.
Over the same ten years, it says, a structural fall in Korea’s planted area limited total output, even as world supply grew. This page stays with those dated counts and with that hypothesis; it does not add a later official tally.
— Contents and key concepts
A hypothesis beyond what has been observed
The essay starts from a hypothesis, not from a season that has already arrived. What if, from July to September, the daily average in Korea sat near 40°C, and the night did not fall below 30°C? The writer is careful to say that this would go well beyond what has been observed. Korea did have spells, in 2018 and in 2022, when the daily average stayed above 30°C.
Under the harsher hypothesis, a night that stays hot would raise respiration, so carbohydrates made by day are spent before they can be stored as starch. In 2018, coastal paddies of Gyeongnam and Jeonnam that headed while the night stayed above 27°C saw sterility rise by an average of more than 20 percent. Night-heat experiments reported from Kyushu and from parts of southern China found that when the night exceeded 28°C, the share of perfect grains in brown rice fell by 15 to 20 percent. Those results stay in the accounts as given.
Varieties, a short-term response, and dated world output
Photosensitive varieties may flower late or unevenly when lasting heat confuses a day-length cue. Temperature-sensitive varieties, often grown where a cool night helps ripening, can lose that advantage, with roots under strain. Short-season types keep a more predictable heading date, so sowing can still be shifted, but grain filling may be too short. Short-term answers include irrigation with cool water held at 22 to 24°C, shade nets, less nitrogen before heading, and the Rural Development Administration lines Nampyeong and Jinsu.
Drawing on FAOSTAT and USDA figures, the essay puts world paddy output at about 700 million tons in 2013 and close to 800 million tons in 2023, with Asia holding about 90 percent of that harvest. Over the same ten years, it says, a structural fall in Korea’s planted area limited total output, even as world supply grew. This page stays with those dated counts and with that hypothesis. The same Korean report, at fuller length, is on CampusDown.
Sources
- Hypothesis, not an observed season: July–September daily average near 40°C, night not below 30°C, said to exceed past observations. Spells with daily average above 30°C in 2018 and 2022. Night heat raises respiration and spends daytime carbohydrates before starch storage. Heat at heading and grain filling after the monsoon; pollen germination checked; panicle form may be distorted. 2018 coastal Gyeongnam and Jeonnam: paddies heading while night >27°C, sterility up by an average of more than 20%. Night-heat experiments from Kyushu and southern China: night >28°C, perfect grains in brown rice down 15–20%, protein up, eating quality down — left in those accounts. Ordinary Korean summer about 25–28°C; threshold about 35°C for enzymes such as Rubisco. Photosensitive varieties: day-length cue, delayed or uneven heading. Temperature-sensitive: inland/upland cool nights, root strain. Short-season types: more predictable heading, risk of unripe grain. Short-term: cool irrigation 22–24°C, shade nets or edge trees, less nitrogen before heading, sowing shifts of limited use if heat lasts months. RDA heat-tolerant lines Nampyeong and Jinsu, as named. FAOSTAT and USDA: world paddy about 700 million tons in 2013, close to 800 million tons in 2023; Asia about 90%. Korea, over the same ten years: structural fall in planted area limited total output. This page stays with those dated counts and that hypothesis and does not add a later official tally.
Last updated: 14 November 2026
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