J. Richter-Menge1, M. L. Druckenmiller2, and M. Jeffries3
1University of Alaska Fairbanks, Institute of Northern Engineering, Fairbanks, AK, USA
2National Snow and Ice Data Center, Boulder, CO, USA
3Cold Regions Research and Engineering Laboratory of the Engineer Research and Development Center, U.S. Army Corps of Engineers, Hanover, NH, USA
The 12 essays featured in Arctic Report Card 2019 provide comprehensive summaries of key land, ice, ocean, and atmosphere observations made throughout the Arctic in the context of historical records. Taken together, the essays also serve to highlight the many strong and complex connections within the Arctic system. It is these connections that magnify the impact of the changing Arctic environment—changes that affect ecosystems and communities on a regional and global scale.
At the center of the changes observed throughout the Arctic is the persistent warming of the surface air temperature, which began around 1980. At +1.9°C, the annually-averaged land-based surface air temperature anomaly for October 2018-September 2019 is the second highest value (after 2015/16) since 1900. Annually averaged Arctic air temperatures for the past six years (2014-19) all exceed previous records since 1900.
In the marine environment, the decline in the extent and thickness of the Arctic sea ice cover is directly linked to the warming air temperatures. In September 2019, the end-of-summer minimum extent of the sea ice cover was tied for the 2nd lowest (with 2007 and 2016) in the 41-year satellite record. The oldest, thickest ice (>4 years old), which was once widespread within the Arctic Ocean, now makes up just a small fraction of the sea ice cover. In March 1985, at the end-of-winter maximum extent, 33% of the ice cover within the Arctic Ocean was made up of very old ice, but in March 2019 old ice constituted only 1.2% of the ice cover. First-year ice now dominates the sea ice cover, comprising ~77% of the March 2019 ice cover, compared to about 55% in the 1980s. Overall, the Arctic sea ice cover has transformed from an older, thicker, and stronger ice mass in the 1980s to a younger, thinner, more fragile ice mass in recent years. Because of this transformation, today’s sea ice cover is now more vulnerable to melting out in summer, thereby increasing the likelihood of a continuing decrease in minimum ice extent into the future.
The declining trend in the extent of the sea ice cover is also directly linked to observed changes in the sea surface temperatures and ocean primary productivity. Sea surface temperatures in the Arctic Ocean are driven mainly by solar warming. Greater solar warming occurs in ice-free regions of the Arctic Ocean, where the dark ocean surface absorbs solar radiation up to 10 times more readily than the brighter sea ice surface, which largely reflects sunlight. August mean sea surface temperatures show significant warming for 1982-2019 in most regions of the Arctic Ocean that are ice-free in August. For instance, the August mean sea surface temperatures in 2019 were ~1-7°C warmer than the 1982-2010 August mean in the Beaufort and Chukchi Seas, the Laptev Sea, and Baffin Bay.
Primary production in the Arctic Ocean is driven by algae growing in the ice (ice algae) and in the water column (phytoplankton), which provide usable energy to the entire food web through photosynthesis. Recent declines in Arctic sea ice extent have contributed substantially to shifts in patterns of primary production throughout the Arctic Ocean, as related increases in light availability and stratification of the water column stimulate the growth of phytoplankton in the water column. These patterns are often associated with the timing of the seasonal break-up and retreat of the sea ice cover: higher production tends to occur in regions where break-up is relatively early, while lower production tends to occur in regions where break-up is delayed. All regions of the Arctic Ocean have exhibited increasing ocean primary productivity over the 2003-19 period, with the most pronounced increases observed in the Eurasian Arctic, Barents Sea, and Greenland Sea.
Recent conditions in the Bering Sea offer an excellent, albeit disquieting, example of the strong connections within the Arctic marine environment. The Bering Sea forms the transition between the sub-Arctic North Pacific and the Arctic Oceans. The eastern half of the Bering Sea has a broad and shallow shelf that enables an exceptionally productive ecosystem, supporting large numbers of sea birds and marine mammals, the subsistence harvests that numerous Indigenous communities depend on, and more than 40% of the U.S. catch of fish and shellfish (valued at > $1B annually). The summer distribution of fishes and invertebrates living near the seafloor on the Bering Shelf is tied to the extent of the cold bottom water temperatures as determined by the southern extent of sea ice during the preceding winter.
For the past two winters (2018 and 2019) the maximum southern sea ice extent in the Bering Sea was at record low values, at approximately 30% of the long-term mean (1980-2010). The record low sea ice coverage was likely a result of three factors: (1) foremost, abnormally warm, southerly winds during winter limited the maximum sea ice extent by pushing the sea ice northward; (2) the late freeze-up of the southern Chukchi Sea in the preceding falls and delayed ice arrival in the northern Bering Sea; and (3) warm surface ocean temperatures that slowed the advance of ice. The record low sea ice extent and early sea ice retreat disrupted the formation of very cold bottom water temperatures on the Bering Shelf. The warmer bottom water temperatures observed during 2018 created a wide corridor within the shallow continental shelf allowing sub-Arctic fish species to move northward into regions typically occupied by northern shelf and Arctic species. In the Atlantic sector’s Barents Sea, there has been a similar northward shift in fish species associated with warming bottom water temperatures and loss of sea ice. Regional patterns of sea ice loss may also be connected to an observed decline in the breeding population of ivory gulls in the Canadian Arctic.
On land, the warming surface air temperature is causing a decrease in the extent of the Arctic snow cover, an increase in the overall amount of Arctic vegetation, and the thawing of perennially-frozen ground, known as permafrost. These components of the Arctic environment are interconnected and understood to influence wildlife. Thawing permafrost detrimentally affects municipal infrastructure, community shorelines, and Indigenous Peoples’ traditional means for storing food in ice cellars. Warming conditions also promote the microbial conversion of carbon that is stored in permafrost into the greenhouse gases carbon dioxide and methane. These gases are released to the atmosphere, further trapping thermal radiation reflected from the Earth’s surface in an accelerating feedback loop to global climate warming. The Greenland ice sheet is also melting under the persistent rise of surface air temperatures and, as a result, contributing to global average sea level rise at a current rate of about 0.7 mm yr-1. During the 2019 melt season, the extent and magnitude of ice loss over the Greenland ice sheet rivaled 2012, the previous year of record ice loss.
Coming full circle, the decreasing extent of sea ice and snow cover along with the melting Greenland ice sheet leads to an acceleration in the rate of warming of surface air temperatures in the Arctic. When these bright, white surfaces melt, they expose darker surfaces (e.g., open ocean, rock, or vegetation). The white surfaces of snow and ice reflect sunlight back to space, helping cool the Arctic region. The darker surfaces of land and ocean absorb sunlight, warming the Arctic region. Hence, the increase in the relative amount of open water and snow-free land leads to warming surface air temperatures, which in turn lead to more melting and more warming. This cycle is a critical reason why the Arctic has warmed at more than twice the rate of the global mean since the mid-1990s, a phenomenon known as Arctic amplification of global warming. This warming is transforming Arctic ecosystems and presenting unique challenges for the region’s Indigenous peoples who rely on the stability of the environment for cultural and economic well-being, as well as for subsistence foods taken from their local lands and waters. The impacts of a changing Arctic are not confined to those who live there. Through global sea-level rise, the release of permafrost carbon, and its role in regulating global weather patterns, the Arctic is vitally connected to people worldwide.
December 6, 2019