Characterizing and Detecting the Influence of Anthropogenic Climate Change on Global Crop Yields

Anthropogenic influence on the climate has now been statistically identified in many physical and biophysical systems. However, no previous studies have directly detected the effect of greenhouse gas emissions in systems dominated by human influence. Here we show that anthropogenic temperature change has had an identifiable impact on yields of the three major field crops - wheat, rice, and maize. We show this by first coupling an empirical yield model with an ensemble of GCM results under both historical forcing and a counterfactual forcing scenario that excludes greenhouse gases. Global yield trends are shown to be lower in the historical forcing case. An index that weights observations by their signal-to-noise ratio (i.e. the strength of the climate change signal divided by the effect of natural climate variability on yields) has more discriminatory power and shows clear separation between the estimated distribution of yields under the historical and counterfactual forcings. Observed yields are consistent with the observed forcing, but not the counterfactual, providing evidence of an identifiable impact of anthropogenic warming on the evolution of global crop yields in the last 50 years.