UM researcher’s study of past planetary cooling offers warnings, strategies for today’s warmup

A University of Montana researcher recently co-authored a paper that provides insight into the ways in which people in ancient Asia adapted their farming and trading practices when the climate cooled about 4,000 years ago.

Their findings offer warnings, and possible strategies, for the global warming now occurring.

Using a computer modeling program and a large ancient grain database, UM researcher Kyle Bocinsky and University of California San Diego assistant professor Jade d’Alpoim Guedes were able to show how a cooling climate affected certain crop yields in Asia from 5,000 to 1,000 years ago.

The paper, published in Science Advances, details the computer model developed by the co-authors and how it shows – for the first time – when and where staple crops were grown in Asia.

Bocinsky is a computational archaeologist who uses computer-based methods to study the past. d’Alpoim Guedes works in the Department of Anthropology and Scripps Institution of Oceanography at UC San Diego and specializes in paleoethnobotany, which involves studying ancient plant remains to understand how human diets changed over time.

Their research shows how people in high-elevation areas of the Tibetan Plateau of central and eastern Asia adapted to a cooler climate by creating trade routes, diversifying to multi-crop yields, migrating, and transitioning from agriculture to pastoralism.

“What this project is, is looking at the adaptation of farmers in a pretty extreme environment,” Bocinsky said. “We started off looking at farmers on the Tibetan Plateau, so this is high-elevation agriculture. People in this region are really impacted by cold temperatures. If the growing season is too short, then their crops are not able to mature and they don’t get yields.”

The researchers studied the growth of six different crops, including broomcorn millet, foxtail millet, wheat, barley, buckwheat and rice.

About 3,500 years ago, foxtail millet and broomcorn would have failed about half the time in high-latitude and high-altitude areas, and farmers eventually favored wheat and barley, which can withstand colder temperatures.

“Around 4,000 years ago, there’s this major shift from a warmer climate to a cooler climate and that impacts the distribution of millets, which were a crop that was actually native to the region in high-latitude and high-altitude Asia, and we see them pulling out of the diet and being replaced by wheat and barley,” d’Alpoim Guedes said.

According to the paper, grains begin to appear at a number of archaeological sites where probabilities of a successful harvest are less than 50 percent, demonstrating the use of trade routes and roads, like the Silk Road.

“We focused on three different potential routes for what we’ve come to know as the Silk Road,” Bocinsky said. “These are corridors of warmer conditions, so either around the southern flanks of the Himalayas, around the northern edge of the Tibetan Plateau or one that goes over the top of the Tibetan Plateau, so those are three sort of hypothesized routes for the Silk Road.”

Upland pastoralists exchanged animal goods for grains grown by rural land farmers in southern Asia. With continual cooling in the Northern Hemisphere, many migrated south. About 1,600 years ago, dynasties moved south to farm millets, wheat and barley.

The climate may even explain why the capital of China was relocated south from Xi’an to what is now Nanjing, the paper suggests.

Between 1,600 and 1,500 years ago, harvests were especially poor, and during the Sui dynasty, the Grand Canal was created to transport grain from Hangzhou in south-central China to Luoyang, Chang’an and to the northern border near Beijing.

About one in eight farmers from northern China moved to southern China during this period, and while warfare played a major role in their migration, cooling temperatures also influenced the decisions.

“What’s interesting to me when I think about adaptation today, is that in the past when we had lower population levels really all over the world, migration was one of those real feasible methods of adapting,” Bocinsky said. “People could move. But we don’t have as much flexibility for migration anymore. You see that in the sort of geopolitical conflict that occurs when immigration happens today due to war or famine.”

While ancient climate change can tell us a lot about what we should expect in the future, human practices have changed, and ancient civilizations had time to adapt to the climate. That may not be the case today, d’Alpoim Guedes said.

“What people often did was they shifted away from growing one single type of crop and they started integrating multiple different types of crops into the diet as a means of coping with this change in climate,” she said. “Part of the issue today is that we’re really moving pretty far away from that. We’re actually moving in the opposite direction, which is a direction where agriculture is centered on a monoculture of either wheat or corn or something like that. But that is a very risky place to be in.”

Climate change is also occurring at a much faster rate now, Bocinsky said.

“The changes that we’re experiencing today are happening on a much shorter time scale and they’re happening all over the world. Certain places are definitely being impacted more than others,” he said.

Bocinsky, who is also a research associate with the Montana Climate Office, helps communicate climate change information to farmers and ranchers in Montana. He said that the information used in the research will be utilized for in-state climate assessments.

“For me, it’s more interesting to have these comparative examples of the full toolkit of adaptations that people have used in the past as a way to think about potential adaptations for the future. In this case, we were able to identify a pretty broad set of strategies people used, from trade, to crop diversification to migration,” Bocinsky said.

In addition, the code used to create the model is open-source and can be used by other researchers to add improvements or new data that could help run this style of reconstruction anywhere in the Northern Hemisphere.

The full study can be found here.