The highlands of the polar ice sheets have cold temperatures to prevent snow metamorphism. However, during warm summers, even if the surface snow does not melt in the highlands, it transforms from fresh snow to coarse snow. This study measured the specific surface area (SSA), a physical parameter used to reconstruct snow metamorphism and a snow grain size, in firn/ice cores drilled in the highlands of the Greenland ice sheet. The SSA decreased with depth because of the increase in the bond diameter between the grains. The depth profile of the SSA undergoes short-term fluctuations, in that the spring and summer layers are lower (larger in snow grain diameter) than the autumn and winter layers each year. We found accelerated snow metamorphism in the period the 1920s–1960s and the 1980s–2020s, corresponding to the warm periods in the Arctic. This indicated that the ice cores preserved the snow metamorphism history when snow accumulated on the Greenland ice sheet.