Credit: Unsplash.

Rice has always been a heat-loving plant, at home in the warm, wet landscapes of Asia. It spread with the first farmers, fed early civilisations, and became one of humanity’s most important staple crops.

But even rice has its limits.

A new study suggests that global warming is pushing major rice-growing regions toward temperatures beyond anything the crop has endured in its 9,000-year history of cultivation. According to the findings, the planet is warming 5,000 times faster than the crop can adapt naturally.

The research combined satellite data, agricultural records, herbarium collections, archaeological evidence from 803 sites and climate models. Its conclusion is stark: domesticated Asian rice has rarely thrived where mean annual temperature exceeds about 28 degrees Celsius, or 82 degrees Fahrenheit, and where warm-season maximum temperatures exceed about 33 degrees Celsius, or 91 degrees Fahrenheit. By the end of the century, large parts of South and Southeast Asia could push beyond those thresholds.

Credit: Unsplash.

Rice is not just another crop. More than half the world’s population depends on it for food, and about 90 percent of production occurs in Asia. Half of all humans get around 20 percent of their calories from rice, meaning more than a billion people rely on its cultivation and distribution for their livelihoods.

That makes rice both a food security issue and a cultural one. In much of Asia, rice paddies are not temporary fields that can be casually moved uphill or northward. They are engineered landscapes, often built and maintained across generations.

“We don’t want to downweight the flexibility of human adaptation,” Nicolas Gauthier, an anthropologist and geographer at the Florida Museum of Natural History and the study’s lead author, told Live Science. “But we also want to acknowledge that these adaptations have already occurred, and in some cases, we might be closer to the limits of what we can reasonably adapt to in that time frame.”

The study shows that rice has adapted before — but mostly in the opposite direction. After its early cultivation in China’s Yangtze region, rice spread north, east and west. Around 4,200 years ago, a period of cooling and drought helped drive the development of cold-tolerant varieties. Those varieties later supported rice farming in more temperate regions, including Korea and Japan.

The hot end of the scale appears less forgiving.

“You don’t see that kind of flexibility on the hot end because at some point, the plant will physically stop working,” Gauthier said.

Rice photosynthesis begins to shut down around 40 degrees Celsius, or 104 degrees Fahrenheit. Heat also damages pollen viability and grain development. In other words, extreme warmth interferes with the machinery that lets the plant reproduce and fill its grains.

A Future without Precedent Archaeological sites where rice has been discovered through time, as shown in 1,000-year time slots beginning with 9,000 years before present. Credit: “Projected warming will exceed the long-term thermal limits of rice cultivation” (2026) by Gauthier et al, CC BY.

To test rice’s thermal range, the researchers compared where rice grows now with where it has appeared in the archaeological record. They used 1,595 dates from 803 archaeological sites and matched them with climate reconstructions across the Holocene, the geological period covering roughly the last 11,700 years.

The pattern held. Across thousands of years of cultivation, rice expanded into cooler regions, split into tropical and temperate varieties and adapted to shorter growing seasons. But it did not break its upper thermal boundary.

The problem is that the kind of warming we expect in the future is not a slow Holocene shift. The study notes that projected climate change is expected to proceed about 5,000 times faster than the rate at which grasses, including many staple crops, have historically shifted their climatic niches.

Under future climate scenarios, major rice-growing areas from India through Southeast Asia and islands in the region are projected to move into conditions with little or no historical analogue for rice cultivation. By 2071 to 2100, parts of India, China, the Middle East, Indonesia and Malaysia are expected to face temperatures beyond one or more of the crop’s historical thresholds.

Regional temperatures are expected to rise beyond the current threshold of rice over the next few decades. Each row corresponds to the results of a separate climate model. Credit: “Projected warming will exceed the long-term thermal limits of rice cultivation” (2026) by Gauthier et al, CC BY.

The risks will not fall evenly. Cooler areas, including parts of northern China or southern Russia, could become more suitable for rice. But that does not solve the problem for farmers in hotter regions.

“You could keep global rice production the same” by moving cultivation around, Gauthier told Live Science. “But that’s not fixing the problem for people who live in South Asia who are relying on rice for their consumption.”

“On an aggregate scale, it could be that, pound for pound, all the rice that won’t be able to grow in Southeast Asia could be grown in China instead, but that doesn’t change the impact on the people in Southeast Asia,” Gauthier said.

Breeding May Help, But Not Enough by Itself Credit: Unsplash.

The study does not argue that rice is doomed. Humans have repeatedly changed rice through selection, breeding, irrigation, timing and landscape engineering. Modern tools like gene editing with CRISPR are also available and will likely be employed, whether some people like it or not. For instance, GMO Golden Rice is engineered to produce beta-carotene, which the body converts into vitamin A. It was designed to address micronutrient deficiencies in rice-dependent populations. Additionally, stored landraces — traditional varieties maintained by farmers — may contain valuable genetic diversity for future heat-tolerant crops.

But adaptation will require money, time, institutions and access. New varieties do not automatically reach smallholder farmers. A heat-tolerant rice plant still needs water, suitable soils, local knowledge and markets.

“These changes are going to be disruptive, and the process of adaptation doesn’t come for free. It has to be done with intention and might not be pleasant,” Gauthier said.

Rice has followed humans through droughts, cold snaps, migrations and empires. The question now is whether human planning can help rice move as fast as the heat.

The findings appeared in the journal Communications Earth & Environment.