A Colder Climate is a Drier Climate

Guest essay by David Archibald

In trying to understand how the US agricultural system will respond to lower solar activity, and thus a posited colder climate, we have to go way back. As far back as the 1970s in fact when it was still possible for academics to publish books and papers on the effects of climatic cooling. In 1977, Reid Bryson and Thomas Murray published a book entitled Climates of Hunger. The book is old enough that Stephen Schneider is credited with reviewing the manuscript, from his time as a cooling alarmist. 

In their discussion of the climate of the Corn Belt, they start with the results of the archaeological excavation of an Indian village called Mill Creek Site B which was occupied from 900 to 1400 AD. This site is in northwest Iowa in the heart of the modern Corn Belt:

To put that into context, there were possibly over one thousand Indian villages on the Great Plains from Iowa to Colorado during the Medieval Warm Period. In the early 19^th century when the explorers who spearheaded the European invasion of the American heartland crossed the plains, they found no corn-farming villages. They left behind the last of the agricultural tribes as they moved out onto the grasslands – the Akira and Mandan on the Missouri and the Pawnee in eastern Kansas – not to find corn fields again until reaching the Pueblos in the southern Rockies. Remnants of the villages were uncovered in the early 20^th century as layers of debris covered by wind-blown soil.

The Indians at Mill Creek farmed corn and hunted elk, deer and bison as well as other animals. This is how the excavation data plotted up relative to time:

Figure 3.3 shows the percentage of each of the major hunted species at Mill Creek Site B over the 500 years from 900 to 1400 AD. Bison eat grass and deer browse on trees. The increasing proportion of bison reflects a drying climate with trees being replaced by grass. Figure 3.4 shows that the number of animals in the diet peaked in the 12^th century. Figure 3.5 shows that the number of potsherds remained high after bone counts first dropped. The authors believed that corn production and potsherds were related because pottery was needed to store, cook and serve corn. The potsherd count, if read as reflection of the total number of people in the village, indicates that the total number of people in the village did not decline immediately with the reduction in game. The numbers of bones and sherds both dropped rapidly after 1300. By 1400 there were none, and no Indians either. Farmers did not occupy the region again until the mid-19^th century.

In their analysis, Reid and Bryson place a lot of emphasis on wind direction. For example Fort Winnebago in Wisconsin kept weather records from 1828 to 1845. Fort Winnebago is now the town of Portage. In 1968, Professor Wahl at the University of Wisconsin-Madison compared the temperatures recorded then with records from 100 years later. His results are shown in the following table:

In every month except March, the 1800s were cooler with the biggest differences in autumn – almost seven degrees in September. Month-by-month comparisons are more important than yearly averages because they have greater implications for food production. Spring and fall temperatures determine the length of the growing season. Calculating the effect on growing degree days (GDD), the climate in the early 1800s had 680 fewer GDD. This would reduce agricultural yield by 27% relative to a 2,500 GDD corn hybrid.

Wind direction was also different with more northerly winds in the 1800s. For Septembers, winds came from the northwest and northeast 47 percent of the time in Fort Winnebago. One hundred years later, Portage records shows winds from these directions 27% of the time. Wind direction also controls rainfall with westerly winds being drier. Reid and Bryson make a stab at calculating this effect in the following figure:

This is Figure 3.1 on page 32 of Climates of Hunger. It is a map of the United States showing July precipitation decreases to be expected with a slightly expanded flow of westerlies, based on 20 years of modern weather records. Shades areas have less rainfall when westerlies are expanded. The combination of lower temperatures and lower rainfall will be a real killer. It killed off the Indian farmers on the Great Plains.

David Archibald, a Visiting Fellow at the Institute of World Politics in Washington, D.C., is the author of Twilight of Abundance: Why Life in the 21^st Century Will Be Nasty, Brutish, and Short (Regnery, 2014).