Longwave Radiation Variability in the Arctic: Forty Years of Change Under Reducing Global Anthropogenic SO₂ Emissions

This study presents a comprehensive assessment of longwave radiation variability in the Arctic based on unique measurements collected at the North Pole drifting station SP‑28 in 1987. The primary objective is to compare these historical observations with modern datasets from the Surface Heat Budget of the Arctic Ocean (SHEBA, 1997–1998) and the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC, 2019–2020) to evaluate long‑term changes in the Arctic radiation regime. Continuous longwave radiation measurements were obtained using high‑precision spectral pyrgeometers to identify Arctic haze. The results show that in 1987, Arctic haze layers enhanced the downward longwave flux by 15–20 W·m-2 and increased atmospheric emissivity. In contrast, MOSAiC observations reveal emissivity values that closely match aerosol‑free model calculations, indicating a substantial decline in Arctic haze and the disappearance of radiatively significant aerosol layers. This shift is in alignment with the long-term reduction of global anthropogenic sulfur dioxide emissions across the Northern Hemisphere.