Martin O. Jeffries1, Jacqueline Richter-Menge2, James E. Overland3
1Office of Naval Research, Arlington, VA, USA
2ERDC-Cold Regions Research and Engineering Laboratory, Hanover, NH, USA
3National Oceanic and Atmospheric Administration, Pacific Marine Environmental Laboratory, Seattle, WA, USA
December 2, 2014
The Arctic Report Card (www.arctic.noaa.gov/reportcard/) considers a range of environmental observations throughout the Arctic, and is updated annually. As in previous years, the 2014 update to the Arctic Report Card describes the current state of different physical and biological components of the Arctic environmental system and illustrates that change continues to occur throughout the system.
Mean annual air temperature continues to increase in the Arctic, at a rate of warming that is more than twice that at lower latitudes. In winter (January-March) 2014, this Arctic amplification of global warming was manifested by periods of strong connection between the Arctic atmosphere and mid-latitude atmosphere due to a weakening of the polar vortex. In Alaska this led to statewide temperature anomalies of +10°C in January, due to warm air advection from the south, while temperature anomalies in eastern North America and Russia were -5°C, due to cold air advection from the north.
Evidence is emerging that Arctic warming is driving synchronous pan-Arctic responses in the terrestrial and marine cryosphere. For instance, during the period of satellite passive microwave observation (1979-2014), reductions in Northern Hemisphere snow cover extent in May and June (-7.3% and -19.8% per decade, respectively) bracket the rate of summer sea ice loss (-13.3% per decade decline in minimum ice extent), and since 1996 the June snow and September sea ice signals have become more coherent.
In April 2014, a new record low snow cover extent for the satellite era (1967-2014) occurred in Eurasia and, in September 2014, minimum sea ice extent was the 6th lowest in the satellite record (1979-2014). But, in 2014, there were modest increases in the age and thickness of sea ice relative to 2013. The eight lowest sea ice extents since 1979 have occurred in the last eight years (2007-2014).
There is growing evidence that polar bears are being adversely affected by the changing sea ice in those regions where there are good data. Thus, for example, between 1987 and 2011 in western Hudson Bay, Canada, a decline in polar bear numbers, from 1,194 to 806, was due to earlier sea ice break-up, later freeze-up and, thus, a shorter sea ice season. In the southern Beaufort Sea, polar bear numbers had stabilized at ~900 by 2010 after a ~40% decline since 2001. However, survival of sub-adult bears declined during the entire period. Polar bear condition and reproductive rates have also declined in the southern Beaufort Sea, unlike in the adjacent Chukchi Sea, immediately to the west, where they have remained stable for 20 years. There are also now twice as many ice-free days in the southern Beaufort Sea as there are in the Chukchi Sea.
As the sea ice retreats in summer and previously ice-covered water is exposed to solar radiation, sea surface temperature (SST) and upper ocean temperatures in all the marginal seas of the Arctic Ocean are increasing; the most significant linear trend is in the Chukchi Sea, where SST is increasing at a rate of 0.5°C/decade. In summer 2014, the largest SST anomalies, as much as 4°C above the 1982-2010 average, occurred in the Barents Sea and in the Bering Strait region, which includes the Chukchi Sea.
Declining summer sea ice extent is also leading to increasing ocean primary production due to solar radiation being available over a larger area of open water. The greatest increases in primary production during the period of SeaWiFS and MODIS satellite observation (1998-2010) occurred in the East Siberian Sea (+112.7%), Laptev Sea (+54.6%) and Chukchi Sea (+57.2%). In 2014, the greatest primary production occurred in the Kara and Laptev seas north of Eurasia. Regional variations in primary production are strongly dependent on the availability of nutrients in the near-surface water layer that receives sufficient solar radiation for photosynthesis to occur.
On land, peak tundra greenness, a measure of vegetation productivity that is strongly correlated with above-ground biomass, continues to increase. The trend in peak greenness indicates an average tundra biomass increase of approximately 20% during the period (1982-2013) of AVHRR satellite observation. On the other hand, greenness integrated over the entire growing season indicates that a browning and a shorter growing season have occurred over large areas of the tundra since 1999. In Eurasia, in particular, these conditions have coincided with a decline in summer air temperatures.
Ice on land, as represented by the Greenland Ice Sheet, experienced extensive melting again in 2014. The maximum extent of melting at the surface of the ice sheet was 39.3% of its area; for 90% of the summer the extent of melting was above the long-term (1981-2010) average; and the number of days of melting in June and July exceeded the 1981-2010 average over most of the ice sheet. Average albedo (reflectivity) during summer 2014 was the second lowest in the period of MODIS satellite observation (2000-2014), and a new, ice sheet-wide record low albedo occurred in August 2014. These signals contrast with the total ice mass, which did not change significantly between 2013 and 2014.
In summary, Arctic Report Card 2014 shows that change continues to occur in both the physical and biological components of the Arctic environmental system. However, it is a complex system and there are spatial and temporal variations in the magnitude and direction of change, and there are some apparent mixed signals. For example, peak tundra greenness increased between 1982 and 2013, but over the length of the growing season there has been an apparent browning of the tundra since 1999, particularly in Eurasia. And, most recently, between 2013 and 2014 there was a modest increase in the age and thickness of sea ice, while mass loss from the Greenland ice sheet was negligible. Nevertheless, overall the long-term trends provide evidence of continuing and often significant change related to Arctic amplification of global warming.