Reconstructed sunspot numbers for 997–7 BC, shown in two panels for better visibility. The black curve, grey shaded area, and red curve depict the mean annual reconstructed SN, its 1σ (68%) confidence interval, and the 22-year smoothed evolution (see main text), respectively. These data are identical to those in Figure 2d. The green curve depicts the decadal SN values reconstructed from multi-proxy cosmogenic isotope data by Wu et al. (2018b) reduced to the ISN-v2 normalisation. The horizontal dashed line marks the SN = 0 line.