Each week the BBC’s engaging “CrowdScience” program takes off on an adventure in response to a question from a listener. In their award-winning entry, producer Cathy Edwards and presenter Marnie Chesterton wound back the clock to three million years ago, the last time the atmosphere contained levels of heat-trapping carbon dioxide comparable to the levels we are experiencing today due to burning of fossil fuels. They visited a monitoring station on the east coast the United Kingdom to describe how current carbon dioxide levels are measured. They spoke to specialists on ancient CO2 trapped in air bubbles in Antarctic ice, on the number of breathing pores, or stomata, of fossil leaves as a clue to ancient CO2 levels, and on the chemical composition of seabed fossils, another clue. They also discussed what the climate was like three million years ago and what kinds of plants and animals were around. They stressed what they learned from the scientists interviewed: “It’s not the level of carbon dioxide per se that we need to worry about, but the speed at which it’s rising.” Christina Horsten, a correspondent for Deutsche Presse-Agentur, said it is “just incredible how one can make a palatable, assessible, fun and entertaining audio piece about a topic that, at first glance, doesn’t lend itself to audio at all. Very well done.” Producer Cathy Edwards said the award is “a tribute to our listeners’ amazing curiosity.” She added, “We thought this question from our listener Thomas was really intriguing: doing detective work into ancient carbon dioxide seemed like a good way to explore ‘how’ we know what we know about climate change.”