After decades of scientific study and political wrangling the world has agreed—at least on paper—that 1.5C of heating must be the upper limit of our impact on the climate system. How could something that sounds so small matter so much?

This is Threshold Season 4: “Time to 1.5.” In this episode, we take you inside the scientific and political origin story of 1.5C, from the holocene to the halls of COP26 in Glasgow.

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