Reply to Gonsamo and Chen: Yield findings independent of cause of climate trends.

Gonsamo and Chen (1) point out that phases of the North Atlantic Oscillation (NAO) and Scandinavia Pattern (SCA) can affect growingseason climate in Europe and therefore crop productivity. However, it is unclear how this observation relates to our paper, which connects the observed long-term trends in climate with changes in yield (2). We state repeatedly in the paper (pp. 2672 and 2674) that attribution of long-term climate trends in Europe to greenhouse gas emissions is beyond the scope of the analysis. The long-term warming over Europe, wetting over northern Europe, and drying over southern Europe that we use to identify impacts on crop yields may be consistent either with anthropogenic climate change or multidecadal patterns of natural climate variability. A formal analysis to attribute long-term climate trends to greenhouse gas emissions requires the use of climate model output to characterize both the distinctive signal of anthropogenic climate change and the magnitude of internal variability (3, 4). Such an analysis is beyond the scope of our paper, and therefore we make no claims regarding the cause of the observed long-term climate trends in Europe, which is the focus of the letter by Gonsamo and Chen.