What stays frozen, and what thaws

Arctic tundra is underlain by a layer of permanently frozen soil called permafrost, which is permanently frozen ground that affects nearly everything in the Arctic ecosystem, including soils, vegetation, water, and wildlife. [NPS Arctic] During summer months, the top layer of soil thaws — known as the active layer — creating a wet landscape with rapid runoff. [NPS Arctic]

An aerial view of autumn-red tundra cut into a quilt of polygons, with darker wetter ground inside some of the shapes — An aerial view of tundra polygons in Alaska, photographed on 5 September 2012, with autumn-red vegetation around the polygon edges. The file does not name a specific park. The pattern is a sign of underground permafrost, and this is Arctic tundra, not alpine tundra in the Rockies.National Park Service · Public Domain (NPS)

An aerial view of a snowy tundra landscape marked by a tight network of polygonal cracks and ponds — An aerial view of ice-wedge polygons on the tundra at Cape Krusenstern National Monument, in the Western Arctic National Parklands of northwest Alaska, photographed on 31 January 2013. This is Arctic patterned ground, not alpine tundra in the Rockies.National Park Service · Public Domain (NPS)

Alpine tundra is distinguished from Arctic tundra, that page says, in that alpine tundra typically does not have permafrost and alpine soils are generally more porous than Arctic soils. [NPS Arctic] Permafrost, which the park defines as an area with a permanently (year-round) frozen subsurface soil layer, is common and widespread in arctic tundra, but patchier within alpine tundra. [NPS Rocky Mountain]

The Arctic-overview page says alpine tundra typically does not have permafrost, and that alpine soils are generally more porous. Rocky Mountain National Park says permafrost is common and widespread in arctic tundra, but patchier within alpine tundra. Both sentences stay on this page.

Low, rolling Arctic tundra with polygonal patterning and several distinct rounded mounds under a cloudy sky — Tundra polygons and pingos — the hill-like mounds formed with water and permafrost — in Bering Land Bridge National Preserve, Alaska, photographed on 12 August 2007. This is Arctic tundra on the Bering Land Bridge, not alpine tundra in the Rockies.Bering Land Bridge National Preserve, National Park Service · CC BY 2.0

NOAA’s Arctic Report Card 2022 says the circumpolar average peak tundra greenness value in 2022 declined from the record high values of the previous two years, but still represented the fourth highest value since 2000. [NOAA] Satellite observations, NOAA writes, made a phenomenon known as “the greening of the Arctic” evident, a change dynamically linked with Earth’s changing climate, permafrost, seasonal snow, and sea-ice cover. [NOAA]

NOAA’s 2022 greenness figure is a circumpolar Arctic observation, not a measurement of Colorado alpine turf. It belongs with the Arctic ring of the year-wheel, not with the Rocky Mountain summer dates.

What stays frozen, and what thaws

Sources on this page