Life is underpinned by fungi. Fungal filaments extend through the soil in networks of mycelia, but we know relatively little about them and questions abound, including where on Earth they are and in what diversity and abundance. Vast and powerful, mycelial networks sequester carbon, hold soils together and supply as much as 80 per cent of all nutrients to terrestrial plants. In just one hectare of grassland, the extent of fungi is equivalent to around 12 million times the length of the Amazon River. But just like the distributions of plant species, those of fungi are almost certainly shifting in response to climate change.