The fingerprint of climate trends on European crop yields

Abstract

Europe has experienced a stagnation of some crop yields since the early 1990s as well as statistically significant warming during the growing season. Although it has been argued that these two are causally connected, no previous studies have formally attributed long-term yield trends to a changing climate. Here, we present two statistical tests based on the distinctive spatial pattern of climate change impacts and adaptation, and explore their power under a range of parameter values. We show that statistical power for the identification of climate change impacts is high in many settings, but that power for identifying adaptation is almost always low. Applying these tests to European agriculture, we find evidence that long-term temperature and precipitation trends since 1989 have reduced continent-wide wheat and barley yields by 2.5% and 3.8%, respectively, and have slightly increased maize and sugar beet yields. These averages disguise large heterogeneity across the continent, with regions around the Mediterranean experiencing significant adverse impacts on most crops. This result means that climate trends can account for ∼ 10% of the stagnation in European wheat and barley yields, with likely explanations for the remainder including changes in agriculture and environmental policies.

Keywords: Europe; adaptation; agriculture; attribution; climate change.

Fig. 1.

Patterns and time evolution of crop yields in Europe and the predicted impacts of climate trends. (A) Area-weighted yields of the four crops examined in this paper for the countries included in the study, 1960–2010 (SI Appendix, Table S1) (17). (B–E) Maps of the observed linear trend in yield in 1989–2009 for wheat (B), maize (C), barley (D), and sugar beet (E) (25). Maps of the expected change in yield based on growing-season temperature and precipitation trends in 1989–2009 (27, 28) and the yield response functions described by Moore and Lobell (8) (SI Appendix, Figs. S3 and S4) for wheat (F), maize (G), barley (H), and sugar beet (I). White shows areas not included in the study due to insufficient data.

Fig. 2.

Impacts of growing-season temperature and precipitation trends in 1989–2009 on European crop yields by country and for the whole region (Total). Impacts are weighted by regional production of the relevant crop in 1989–1994 (Methods). The black line shows impacts calculated using the regression point estimate (Table 1), and the colored bars show the 90% confidence interval obtained by inverting a two-tailed hypothesis test of size 10% (Methods). This distribution is skewed for wheat, maize, and sugar beet yields, which is why the bars are asymmetric around the point estimate.

Fig. 3.

Spatial fingerprint of trends in growing-season temperature and precipitation in 1989–2009 on wheat (A), maize (B), barley (C), and sugar beet (D) yields. The maps show the predicted trends in crop yield due to temperature and precipitation changes (Fig. 1 F–I) corrected by the regression coefficient $\widehat{{\beta }_1}$(Table 1). White shows areas not included in the study due to insufficient data.