Table 1.

Results of test 1, the detection of the impact of long-term climate trends on European crop yields

Row name	Wheat yield	Maize yield	Barley yield	Sugar beet yield
Regression coefficient $\left({\beta }_1\right)$	0.41	1.39	0.50	0.82
SE	0.10	0.88	0.34	0.81
Test statistic (${\tau }_1$)	4.03	1.58	1.47	1.00
P(${\tau }_1|H_0$)	<0.002	0.002	0.012	0.02
Degrees of freedom	349	267	341	183
Adjusted R2	0.07	0.10	0.06	0.28

The null hypothesis is rejected for all crops at the test size of 5%. Significance levels are determined by a block-bootstrapping procedure that includes resampling the parameters of the climate-yield response function (Methods). Although centered on zero, this distribution is skewed to the left, meaning critical values are lower than under standard normality assumptions [critical values for a one-tailed test under the normal approximation are 1.64 (5%) or 1.28 (10%)].