finding 26.2 : key-message-26-2

Alaska residents, communities, and their infrastructure continue to be affected by permafrost thaw, coastal and river erosion, increasing wildfire, and glacier melt. These changes are expected to continue into the future with increasing temperatures, which would directly impact how and where many Alaskans will live (very likely, high confidence).

This finding is from chapter 26 of Impacts, Risks, and Adaptation in the United States: The Fourth National Climate Assessment, Volume II.

Process for developing key messages:

The Alaska regional chapter was developed through public input via workshops and teleconferences and review of relevant literature, primarily post 2012. Formal and informal technical discussions and narrative development were conducted by the chapter lead and contributing authors via email exchanges, teleconferences, webinars, in-person meetings, and public meetings. The authors considered inputs and comments submitted by the public, the National Academies of Sciences, Engineering, and Medicine, and federal agencies. The author team also engaged in targeted consultations during multiple exchanges with contributing authors, who provided additional expertise on subsets of the Traceable Account associated with each Key Message.

Description of evidence base:


Multiple studies of permafrost in Alaska have shown that the gradual warming of the ground5a612de8-a07d-48c0-a7ca-c4b705157070 has resulted in the warming and thawing of permafrost over the past 30 years,7fbfdebd-eb73-40be-88ec-109ad7a226fd,177a411e-625e-4fdd-b95b-17e93b2a37bc,aefcf032-770b-4cff-a18d-0a977a83e7bf and spatial modeling projects that near-surface permafrost will potentially disappear on up to a quarter of the landscape by the end of the 21st century.b1ddb024-70ac-41a2-8265-5eeca20538f0 The magnitude of these changes depends on climate and ground-ice conditions, where permafrost thaw generally results in drier upland habitat and wetter lowlands as tundra and forests are converted to lakes and bogs.aefcf032-770b-4cff-a18d-0a977a83e7bf,dc223983-2a34-4be2-8ee8-a885f4b28ab4 These changes will undoubtedly result in a number of societal consequences, loss of wildlife habitat, damage to infrastructure (including buildings, airport runways, tank farms, and roads), ecosystem contamination, and increased maintenance costs.269e8640-18d1-4f61-aa0f-55eb3fbea2d2,b7e764c8-8912-4d18-8dd3-1555ab8da1c2,df6fcad4-f0ea-4c60-97e1-ae2a40455f51,e20d63e1-6f4a-4ffe-a1ac-69b51b6a295b,f9199c06-d3be-4994-a638-226cdc4ebc88,343b40b2-94e2-4749-89ab-c7cd5235bf01


It has been well documented that wildfires are a common occurrence in Alaska, especially the interior boreal areas, although they have also occurred in areas of arctic tundra,9e7065c6-93b9-4bf7-8883-3547a9199ea6,b7e45934-e429-4495-bf93-715a077f0353 with some of the largest fire years (1–6 million acres) occurring between 2004 to 2016 since records began around 1950.9e7065c6-93b9-4bf7-8883-3547a9199ea6 Recent studies show that changes in wildfire across the Alaska landscape could be attributed to human activity.f0da0f34-a262-4055-8315-5d1257e6bd3e This has resulted in changes in boreal vegetation cover53dfec62-ef52-4549-98e3-594adb51d9d6,0ea0a631-70cd-4acd-b9c2-053e4533d8d5 and tundra communities.b7e45934-e429-4495-bf93-715a077f0353 The increased fire frequency of recent decades is expected to continue into the future, in spite of the change to less flammable deciduous vegetation, because of the accompanying change to warmer and drier conditions.53dfec62-ef52-4549-98e3-594adb51d9d6 The ground is warmer under post-fire deciduous vegetation, and thus fires will enhance the thaw of permafrost that is already underway due to climatic warming.e7511bb0-eba5-447e-a035-0c470c871b1c

Coastal and River Erosion

The shoreline along Alaska's northern coast has eroded at some of the fastest rates in the Nation, putting local communities, oil fields, and coastal habitat at risk.cf15559b-f1e8-4022-945b-45ab149dc1a8 Unlike the contiguous United States, Alaska is subject to glacial and periglacial processes that make permafrost and sea ice key controlling factors of coastal erosion and flooding. Thermal degradation of permafrost leads to enhanced rates of erosion along permafrost-rich coastal shorelinescf15559b-f1e8-4022-945b-45ab149dc1a8 and subsidence of already low-lying regions. Longer sea ice-free seasons, higher ground temperatures, and relative sea level rise are expected to exacerbate flooding and accelerate erosion in many regions, leading to the loss of more shoreline in the future.cf15559b-f1e8-4022-945b-45ab149dc1a8

While erosion and changed river courses are a normal part of landscape evolution, lateral river erosion rates are likely to change over time, but the direction and magnitude of these changes are poorly understood. Major river erosion events are typically tied to high hydrological flows or the melting of permafrost along river and stream banks. Statewide, evidence for changes in maximum gauged streamflows is mixed, with a majority of locations having no significant trend.41ed988f-4fa6-476d-90c9-ef9e3e8d1806 There is significance for seasonal changes in the timing of peak flows in interior Alaska, though increases in the absolute magnitude are not well evident in existing data.5e61fa98-c1ff-42e6-aa82-10dad90342d9 Riverine erosion is a serious problem for a significant number of communities.49a37e8f-eef6-4ee6-9705-fac54c48df30 Significant resources have been expended to slow erosion at some communities, often through the construction of berms and bank stabilization projects. These projects have a mixed record of success and nearly always require ongoing maintenance.

Glacier Change

Airborne altimetry surveys of Alaska glaciers spanning the 1994–2013 interval and covering about 40% of the region’s glacierized areadf531aa2-4a99-4ce7-9dd9-744729e2161d yield decadal timescale mass balance estimates for individual glaciers and a regional estimate.08047702-47b0-4401-ab44-a0f46a16efe5 Several new modeling studies suggest that the measured rates of Alaska ice loss are likely to increase in coming decades,c426adb7-b055-4726-80f1-82d7846f46c0,1fe625fe-eaad-48b2-a0c6-5943f14f41e0,54da0d51-35de-45e1-b367-7d0f983e3547,226e7316-1460-4cfe-94a1-4bca27549241 with substantial regional-scale reductions in glacier area, volume (up to 40%–60% loss), and number. Moreover, physically based runoff models suggest that runoff from glaciers accounts for almost 40% of the total freshwater discharge into the Gulf of Alaska.8a321a2e-ffd9-45d6-8d5b-7d1ef8c5df47

Interdisciplinary research along the Gulf of Alaska is providing new insights into the role of glacier runoff in structuring downstream freshwater and nearshore marine ecosystems.141ed68e-5810-4735-afee-878ceb6041cc End-of-century projections from physically based models suggest that anticipated atmospheric warming (2°–4.5°C) will drive volume losses of 32%–58% for Alaska glaciers.226e7316-1460-4cfe-94a1-4bca27549241 Increases in river chemical ions due to glacial runoff and permafrost melt have also been associated with diminishing glaciers in Alaska.7c14626a-343f-48a3-9076-1bd656f663c3,08047702-47b0-4401-ab44-a0f46a16efe5

New information and remaining uncertainties:

Some events such as wildfires and coastal storms are dependent on regional and local current weather conditions, and the exact landscape or ecosystem response can be highly variable. Future effects are also dependent on quick response actions and adaptation measures.

Assessment of confidence based on evidence:

There is high confidence that wildfire in Alaska will continue but medium confidence as to its ultimate effect on vegetation and permafrost, which is often dependent on fire fields available (e.g., older forests or new growth shrublands), the fire intensity, and the return rate. There is high confidence that the north coast of Alaska is eroding at high rates. It is likely that coastal erosion is accelerating in response to climate change but medium to low confidence as to the location and rate because of limited studies and datasets documenting this. There is high confidence that river erosion will continue but medium confidence as to when, where, and to what extent this will occur across Alaska because of differences in local climatic and geographic qualities of the area in question. There is high confidence and it is likely that the glaciers in Alaska will continue to diminish, especially those that are tidewater glaciers.

This finding was derived from scenario rcp_4_5
This finding was derived from scenario rcp_8_5

References :

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