Nearly fifty years ago —things were up and running by March 1958 — Charles Keeling and colleagues began a series of measurements of atmospheric CO₂ on Mauna Loa in Hawaii. The results, made graphic in the jagged 'Keeling curve' running across this week's cover, made the world take notice — eventually. The Mauna Loa measurements constitute the longest continuous record of atmospheric CO₂ in the world. The steady rise in CO₂ that they record now forms the accepted backdrop to today's climate science and economic and political decision making. As well as being an important resource in itself, the Mauna Loa record highlights the vital importance of Earth monitoring programmes. The fiftieth anniversary of the start of this work is marked in this issue by News Features and other pieces on the Earth monitoring being done today, historical pieces on the Mauna Loa data and more.