Carbon dioxide levels in our atmosphere today are higher than at any point in human existence. But going back further into Earth’s history, when do we find concentrations as high as they are now - and what was the planet like back then?

CrowdScience sets out to answer our listener Thomas’s question, travelling back through time with the help of Antarctic ice cores, ancient plant fossils, and microscopic popcorn-shaped organisms called foraminifera, all of which hold clues to past climates.

Enlisting the help of chemists, botanists and palaeontologists, we find out about the huge swings in atmospheric carbon dioxide from prehistoric times to the present day, and ask the all-important question: can this help us understand what's happening to our climate now?

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Presenter: Marnie Chesterton

Producer: Cathy Edwards

(Image: Polar bear on an ice floe. Credit: Getty Images)