Climate change is, arguably, the biggest environmental challenge the global population faces today. To address this major issue, decision-makers not only need accurate information on how our world is changing now, but also predictions on what may happen in the future. A sound knowledge of how Earth behaves as one system is the foundation to all of this – and the pieces of this complex puzzle come largely from satellites orbiting our planet. To ensure that data from Earth-observing satellites are used to their best advantage, further science and, ultimately, bring the most benefit to humankind, ESA and NASA have formed