Warning signs of climate change are all around us, from pictures of polar bears slipping off melting glaciers to the blinking countdown clock in New York City’s Union Square, which tells how much time is left before the warming planet reaches a point of no return. A new exhibition at Guggenheim Bilbao zeroes in on the environment past and present. It looks at land art that still exists or has been reconstructed, and examines artistic practices inspired by issues of sustainability, i.e. shifts in materials, the recycling of materials, and ideas about ancestral wisdom. This is a cerebral show founded on a product that formed on Earth around 500 million years ago—soil. —Maggie Turner