Whereas climate change on a global scale is driven largely by greenhouse gases, with a smaller contribution from absorbing and scattering aerosols in the atmosphere, there are indications in the Hindu Kush Himalayan (HKH) region that absorbing aerosols containing large amounts of black carbon are playing a significant, perhaps even dominant, role in changing the region’s climate. This information sheet provides a brief description of black carbon in the atmosphere, its sources, and its impacts in the HKH region.