evidence: In the years since his seminal testimony, many of Hansen’s basic scientific predictions about the Earth’s climate future have come true. Greenhouse gas emissions have grown, and global temperatures have continued to rise. The world’s glaciers and ice sheets are melting and sea level rise is accelerating. [...] A gradual global decline in air pollution, driven by tightening environmental regulations, is part of the reasoning. Some types of air pollution are known to have a cooling effect on the climate, which may mask some of the impact of greenhouse gas emissions. As these aerosols decline in the atmosphere, some research suggests, this masking effect may fall away and global temperatures may rise at faster rates. [...] Climate change, caused by human greenhouse gas emissions, is in itself a form of planetary geoengineering, he added.