Today, the topic of climate change is a major part of daily life, yet 40 years ago it was virtually unheard of. Since then, Horizon and the BBC have followed scientists as they have tried to unpick how the climate works and whether it is changing. Dr Helen Czerski delves into this unique archive to chart the transformation of a little-known theory into one of the greatest scientific undertakings in history. It has been a constantly surprising journey of discovery that has revolutionised our understanding of climate, and seen scientists face unprecedented controversy and criticism.