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How much have crop yields fallen in the American farm belt as growing-season temperatures have dropped over the last several decades?

askamerica run · 2026-09-11

## Answer

Both premises of this question are false, so it cannot be answered as asked.

**Growing-season temperatures in the farm belt have not fallen over the last several decades.** There was a real, documented mid-20th-century "warming hole" in the Corn Belt — summer daytime highs dipped from roughly the late 1950s through the 1980s/90s even as the globe warmed overall, plausibly tied to irrigation expansion and denser, more productive cornfields raising evapotranspiration (an agriculture-driven regional cooling effect, not a natural climate trend). But that period is not "the last several decades." Looking at the actual recent record, a University of Illinois farmdoc daily analysis of Corn Belt monthly temperature and precipitation (1980-2023) found only one of a dozen weather variables tested showed a statistically significant trend — essentially no robust directional signal, up or down, in the period that matters for current yields. Where anything has moved recently it is nighttime and winter temperatures trending up. NASA and USDA ERS both describe Corn Belt temperatures as expected to continue warming, not cooling.

**Crop yields have risen dramatically over the last several decades, not fallen.** Queried directly from USDA NASS QuickStats via `ag.nass_crop_production` (AskAmerica connector), commodity CORN, statisticcat_desc YIELD, unit_desc BU/ACRE, state-level rows for IA, IL, IN, NE, MN, OH, 1995-2025: state-average corn yield rose from roughly 105-115 bu/acre in the mid-1990s to 200-214 bu/acre in 2023-2025 — essentially a doubling. There are year-to-year dips (2012's drought is the clear low point in the series), but the multi-decade trend is strongly upward, driven mainly by hybrid seed genetics and improved management practices, not temperature.

A chart titled "US Corn Belt corn yield, 1995-2025 (avg of IA, IL, IN, NE, MN, OH state yields)" was rendered from this query, climbing from ~109 to ~203 bu/acre over the period — the opposite of the question's premise.

## What could be answered instead

If the real interest is how climate variability affects Corn Belt yields, the honest framing is: yields have risen sharply due to technology, and weather shows up mainly as year-to-year volatility (e.g., the 2012 drought) superimposed on that rising trend, not as a multi-decade decline from cooling. A regression of yield on growing-season temperature/precipitation with year fixed effects (to strip out the technology trend) would quantify that volatility, but it requires joining a temperature series from the `weather` schema (NOAA GHCND), which was not pulled in this pass.

## Sources

- [US corn belt defies global warming trend — IFT.org](https://www.ift.org/news-and-publications/news/2019/october/29/us-corn-belt-defies-global-warming-trend)
- [Warming temperatures in U.S. Corn Belt expected to continue into next decade — USDA ERS](https://www.ers.usda.gov/data-products/charts-of-note/chart-detail?chartId=108037)
- [Trends in Monthly Temperature and Precipitation for the U.S. Corn Belt — farmdoc daily (2024)](https://farmdocdaily.illinois.edu/2024/05/trends-in-monthly-temperature-and-precipitation-for-the-us-corn-belt.html)
- [How US Corn Farmers Adapted to Climate Change — AIP.org](https://www.aip.org/inside-science/how-us-corn-farmers-adapted-to-climate-change)
- USDA NASS QuickStats corn yield data, queried directly via `ag.nass_crop_production` (AskAmerica connector, commodity_desc='CORN', statisticcat_desc='YIELD', unit_desc='BU / ACRE', state_alpha IN ('IA','IL','IN','NE','MN','OH'), agg_level_desc='STATE', years 1995-2025)