The assessment, for the first time, integrates the climate and air-pollution costs and benefits from methane mitigation. Because methane is a key ingredient in the formation of ground-level ozone (smog), a powerful climate forcer and dangerous air pollutant, a 45 per cent reduction would prevent 260 000 premature deaths, 775 000 asthma-related hospital visits, 73 billion hours of lost labour from extreme-heat, and 25 million tonnes of crop losses annually