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TURMOIL AT THE TOP OF THE WORLD The Arctic’s changing climate is literally turning the tundra upside down. The texture of the summer tundra is biz arre when seen from above. It looks like crocodile skin: a watery expanse of patterned brown and green. This signature landscape is the result of complex interactions between soil and water at high latitude. But those interactions are being disrupted by a rapidly changing climate, and the pattern of the tundra is gradually being inverted—what once was low and wet is now high and dry, and vice versa. Recent work by Los Alamos geomorphologist Cathy Wilson, as part of a large multinational collaboration, has revealed that the changes are happening faster than previously appreciated. “These findings are exciting but scary. I really hope this work helps the general public and policy makers understand just how vulnerable the Arctic is to climate change,” says Wilson. Not far beneath the surface, interspersed throughout the frozen soil are large vertical wedges of ice—the gradual product 15 About four million people in eight different countries live in the Arctic: the United States, Canada, Greenland (Denmark), Iceland, Norway, Sweden, Finland, and Russia. There is considerable variability in the Arctic climate, with winter temperatures occasionally dropping below -50°C (-58°F) and summer highs sometimes exceeding 30°C (86°F). 12 1663 July 2016 of water repeatedly trickling into crevices and then freezing. The ice wedges are conspicuous because the topsoil above them is raised into ridges (the result of water’s expansion upon freezing). Ordinarily, these ridges abut one another, forming a network of meters-wide polygons with comparatively low centers, where ponds form in the summer and snow collects in the winter. As the climate warms, the ice wedges, formed over hundreds of years, are melting from the top down. When the top of an ice wedge melts, the ridge of soil above it collapses into a trough, making the middle of the polygon compara- tively higher, and causing the water from the central pond to drain into the trough. A tipping point arises when enough ridges collapse into troughs because they can connect to form a continuous network that drains these wetland landscapes. The Arctic tundra receives surprisingly little precipitation, so once that water is gone, it’s gone. What used to be a stable and saturated system is transformed into something much drier and entirely new. Wilson and other Los Alamos scientists, along with external collaborators, are hustling to learn as much as they can so they might know what to expect in the future as warming continues. 10 5 1700 plant species and just 48 mammal species live in the Arctic tundra. The Arctic tundra is one of the driest regions on Earth, with less than 10 inches of precipitation per year in most locations—less than the desert states of the American Southwest. The oceans are 30% more acidic than they were when Mozart began composing at age four in 1760. The Arctic ocean is acidifying twice as fast as other oceans.