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.
Over the past five years, ocean acidification (OA) has emerged as one of the most prominent issues in marine research. This is especially true given the newfound public understanding of the potential biological threat to marine calcifiers (e.g. clams, pteropods) and associated fisheries, and the associated human impacts for small communities that directly or indirectly rely on them (e.g., Mathis et al., 2015a; Frisch et al., 2015). Cooler water temperatures and unique physical processes (i.e. formation and melting of sea ice) make the waters of the Arctic Ocean disproportionately sensitive to OA when compared to the rest of the global ocean. Even small amounts of human-derived carbon dioxide (CO2) can cause significant chemical changes that other areas do not experience, and these could pose an existential threat to some biological organisms.
The Arctic is an integral part of the larger Earth system where multiple interactions unite its natural and human components. As is amply demonstrated in each annual installment of the Arctic Report Card, the domain is collectively experiencing rapid and amplified signatures of global climate change. At the same time, the Arctic system’s response to this broader forcing has, itself, become a central research topic, given its potential role as a critical throttle on future planetary dynamics (NRC 2013, 2014). Changes are already impacting life systems, cultures and economic prosperity and continued change is expected to bear major implications far outside the region (ACIA 2005, AMAP 2012, IPCC 2013, Cohen et al. 2014). Ongoing assessments of how the system is wired-together and how sensitive its environment is to change suggest that there are important interconnections and possible feedbacks but these remain highly uncertain (Francis et al. 2009a; Hinzman et al. 2013). We have entered an era when environmental management, traditionally local in scope, must confront regional, whole biome, and pan-Arctic challenges but also requires policy development that crosses scales and boundaries from villages to international partnerships.
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 Arctic continues to warm at a rate that is currently twice as fast as the global average. Warming is causing normally frozen ground (permafrost) to thaw, exposing significant quantities of organic soil carbon to decomposition by soil microbes (Romanovsky et al. 2010, Romanovsky et al. 2012). This permafrost carbon is the remnants of plants, animals, and microbes accumulated in frozen soil over hundreds to thousands of years (Schuur et al. 2008). The northern permafrost zone holds twice as much carbon as currently in the atmosphere (Schuur et al. 2015, Hugelius et al. 2014, Tarnocai et al. 2009, Zimov et al. 2006). Release of just a fraction of this frozen carbon pool, as the greenhouse gases carbon dioxide and methane, into the atmosphere would dramatically increase the rate of future global climate warming (Schuur et al. 2013).
The Arctic sea ice cover is vast in areal extent covering millions of square kilometers, but is only a thin veneer a few meters thick. This ice cover plays many roles. It is a barrier limiting the exchange of heat, moisture, and momentum between the atmosphere and ocean; a home to a rich marine ecosystem, including human communities; and an indicator of climate change. Sea ice extent has been monitored using passive microwave instruments on satellite platforms since 1979. The months of September and March are of particular interest because they are the months when the Arctic sea ice typically reaches its maximum and minimum extent respectively.