Vital Signs

Arctic surface air temperature is an indicator of regional and global climate change. Although there are year-to-year and regional differences in air temperatures due to natural variability, the magnitude and Arctic-wide character of the long-term temperature increase is a major indicator of global warming and the influence of increases in greenhouse gases

Satellite-derived estimates of SCE over Arctic land areas date back to 1967, and have shown dramatic reductions since 2005. This loss of spring snow over Arctic land areas is important because it influences the surface energy budget (snow is highly reflective of incoming solar energy), ground thermal regime (snow is a highly effective insulator of the underlying soil), and hydrological processes (the snowpack stores water in solid form for many months before spring melt).

Reflecting surface air temperature patterns over the Greenland ice sheet, the April 2016-April 2017 season was characterized by relatively low summer (June, July, August) melt extent and ablation along the margins of the ice sheet. Correspondingly, the surface albedo, averaged over the entire ice sheet, was relatively high. The net ice mass loss over the year was near average.

The Arctic sea ice cover varies substantially over the year, with end-of-winter ice cover generally two to three times as large as at the end of summer. Sea ice is an important element of the climate system: (1) acting as a barrier between the underlying ocean and the atmosphere, (2) limiting the amount of absorbed solar energy due to its high albedo, (3) providing a habitat for biological activity, and (4) limiting human access to the Arctic Ocean.

Summer sea surface temperatures (SST) in the Arctic Ocean are set mainly by absorption of solar radiation into the surface layer. In the Barents and Chukchi Seas, there is an additional contribution from advection of warm water from the North Atlantic and Pacific Oceans, respectively. Solar warming of the ocean surface layer is influenced by the distribution of sea ice (with more solar warming in ice-free regions), cloud cover, water color, and upper-ocean stratification. River influxes influence the latter two, as well as provide an additional source of warm water. SSTs are an essential indicator of the role of the ice-albedo feedback mechanism in any given melt season: as the area of ice cover decreases, more incoming solar radiation is absorbed by the ocean and the warmer ocean in turn melts more sea ice.

Autotrophic minute algae living in the sea ice (ice algae) and water column (phytoplankton) are the main primary producers in the Arctic Ocean. Through photosynthesis, they transform dissolved inorganic carbon dioxide into organic material. Consequently, primary production provides a key ecosystem service by providing energy to the entire food web in the oceans.

Vegetation in the Arctic tundra has been responding to environmental changes over the course of the last several decades, with the tendency being an increase in the quantity of above-ground vegetation (i.e. “greening”). These vegetation changes vary spatially throughout the circumpolar Arctic in both direction and magnitude, and they are not always consistent over time. This suggests complex interactions among atmosphere, ground (soils and permafrost), vegetation, and herbivore components of the Arctic system.

Arctic air temperature is an indicator of regional and global climate change. Although there are year-to-year and regional differences in air temperatures due to natural variability, the magnitude and Arctic-wide character of the long-term temperature increase is a major indicator of global warming and the influence of increases in Greenhouse gases (Overland, 2009; Notz and Stroeve, 2016). Here we report on the spatial and temporal variability of Arctic air temperatures during the period October 2015 through September 2016, the 12-month period since the end of the previous Arctic Report Card reporting period.

Snow cover is a defining characteristic of the Arctic land surface for up to 9 months each year, evolving from complete snow cover in the winter to a near total loss of snow cover by the summer. Highly reflective snow cover acts to cool the climate system, effectively insulates the underlying soil, and stores and redistributes water in solid form through the accumulation season before spring melt. Snow on land in spring has undergone significant reductions in areal extent during the satellite era, which impacts the surface energy budget, ground thermal regime (with associated effects on geochemical cycles), and hydrological processes. The loss of spring snow cover is a clear indicator of change in the terrestrial cryosphere, much in the same way summer sea ice loss is indicative of changes in the marine cryosphere.

The Greenland ice sheet plays a crucial role globally and locally, impacting the surface energy budget and climate and weather and contributing to current and future sea level rise.