Boreal forest tipping point and polar habitat change

Boreal forest tipping point and polar habitat changeSpec D4.3.3, D4.3.4

Boreal forests: from carbon sink to carbon source

Boreal forest (taiga) covers much of Canada, Scandinavia and Russia. It has stored huge amounts of carbon in trees and deep soil layers, accumulating more carbon each year than it loses. Climate change could switch it to net carbon loss, an example of a tipping point.

1. Warmer temperatures and decreased winter snowfall mean less meltwater in spring.
2. Drought becomes more frequent, so primary production in the taiga falls.
3. Stressed trees lose needles and die: forest browning.
4. Forest fires become more frequent and intense.
5. Fires burn legacy carbon: old organic matter in deep soil layers that survived earlier, less intense fires.
6. The forest releases more carbon than it absorbs.

Melting of landfast ice and sea ice

Landfast ice is sea ice attached to the coast. Emperor penguins (Aptenodytes forsteri) breed on it in the Antarctic winter, and chicks need stable ice until they grow waterproof feathers. Early breakout of the ice drowns or chills chicks, so breeding grounds can be lost. In 2022, several colonies in the Bellingshausen Sea region lost almost all their chicks this way.

Walruses in the Arctic use floating sea ice as a platform for resting and nursing calves between dives to feed on shellfish on the shallow sea bed. As sea ice retreats, walruses crowd onto beaches in very large groups, where calves can be crushed in stampedes, and must swim further to feed.