Figure 1: 15-year (2000–2014) trends of annual GPP and the three indicators in North America.

(a) Annual GPP. (b) Start of growing season (GSstart). (c) Maximum daily GPP (GPPmax). (d) End of growing season (GSend). A negative sign (red color) in (b) and (d) denotes an earlier trend of GSstart and GSend, and vice versa. Maps were generated using MATLAB 2015b (http://www.mathworks.com/products/matlab/).