Key Findings from the Snow, Water Ice, and Permafrost in the Arctic 2017
a report from the Arctic Council Arctic Monitoring and Assessment ProgramThe following key findings are taken directly from a recent report about the Arctic's cryosphere--the snow, water, ice, and permafrost. As the cryosphere changes, so do the Arctic's physical, chemical, and biological systems with complex consequences within and beyond the region.
Temperatures in the Arctic are rising at least twice as fast as other places due to a number of feedback mechanisms. These feedback mechanisms amplify warming beyond the effects caused by increasing greenhouse gas concentrations alone.
The largest feedbacks, according to climate models, are related to the Arctic's inefficiency at radiating heat. Cold regions radiate heat slowly, so the warmth trapped by greenhouse gases tend to build up. Furthermore, warming in the Arctic is concentrated close to the Earth's surface, slowing the rate at which heat is lost to space from the top of the atmosphere.
The next-largest warming feedback comes from changes in surface reflectivity due to the melting of snow and ice. As reflective surfaces are replaced by darker surfaces, such as open water or land, less energy is radiated back to space and the region warms further, leading to still more melting. Water vapor (a powerful greenhouse gas) also provides a warming feedback. Warmer temperatures increase evaporation, and a warmer atmosphere can hold more vapor.
The following key findings tell us more about the changes occurring in the Arctic.
The Arctic's climate is shifting to a new state.Rising concentrations of greenhouse gases are driving widespread changes in the Arctic's sensitive climate, hydrological, and ecological systems. Since 2011, downward trends have continued in sea ice thickness and extent, land ice volume, and spring snow cover extent and duration, while near-surface permafrost has continued to warm.
With each additional year of data, it becomes increasingly clear that the Arctic as we know it is being replaced by a warmer, wetter, and more variable environment. This transformation has profound implications for people, resources, and ecosystems worldwide.
- The Arctic Ocean could be largely free of sea ice in summer as early as the late 2030s, only two decades from now.
- The recent recognition of additional melt proccesses affecting Arctic and Antarctic glaciers, ice caps, and ice sheets suggests that low-end projections of global sea-level rise made by the Intergovernmental Panel on Climate Change (IPCC) are underestimated.
- Changes in the Arctic may be affecting weather in mid-latitudes, even influencing the Southeast Asian monsoon.
Climate change in the Arctic has continued at a rapid pace.Arctic temperatures are rising faster than the global average. The Arctic was warmer from 2011 to 2015 than at any time since instrumental records began in around 1900, and has been warming more than twice as rapidly as the world as a whole for the past 50 years. January 2016 in the Arctic was 5 degrees C warmer than the 1981-2010 average for the region, a full 2 degrees C higher than the previous record set in 2008, and monthly mean temperatures in October through December 2016 were 6 degrees C higher than average for these months. Sea temperatures are also increasing, both near the surface and in deeper water.
The frequency of some extreme events is changing. Recent observations include a widespread decline in periods of extreme cold during both winter and summer, and increases in extreme warm periods in some areas, such as northern Alaska and northeastern Russia in autumn and spring.
The decline in sea ice continues, with variation from year to year. Sea ice thickness in the central Arctic Ocean declined by 65% over the period 1975-2012. Sea ice extent has varied widely in recent years, but continues a long-term downward trend. A record low minimum sea ice extent occurred in 2012 and a record low maximum sea ice extent occurred in 2016.
Older ice that has survived multiple summer is rapidly disappearing; most sea ice in the Arctic is now "first year" ice that grows in the autumn and winter, but melts during the spring and summer.
Except for the coldest northern regions of the Arctic Ocean, the average number of days with sea ice cover in the Arctic declined at a rate of 10-20 days per decade over the period 1979-2013, with some areas seeing much larger declines. Warm winds during the autumn of 2016 substantially delayed the formation of sea ice. Sea ice is becoming more mobile as its extent and thickness decrease, increasing ice-related hazards. More open water occurs in all months of the year compared with observations reported in 2011.
The area and duration of snow cover are decreasing. Snow cover has continued to decline in the Arctic, with its annual duration decreasing by 2-4 days per decade. In recent years, June snow area in the North American and Eurasian Arctic has typically been about 50% below values observed before 2000.
Permafrost warming continues. Near-surface permafrost in the High Arctic and other very cold areas has warmed by more than 0.5 degrees C since 2007-2009, and the layer of the ground that thaws in the summer has deepened in most areas where permafrost is monitored.
The loss of land-based ice has accelerated in recent decades. Since at least 1972, the Arctic has been the dominant source of global sea-level rise. Seventy percent of the Arctic's contribution to sea-level rise comes from Greenland, which on average lost 375 gigatons of ice per year, the equivalent to a block of ice measuring 7.5 kilometers or 4.6 miles on all sides, from 2011-2014. This is close to twice the rate over the period 2003-2008.
Freshwater storage in the Arctic Ocean has increased. Compared with the 1980-2000 average, the volume of freshwater in the upper layer of the Arctic Ocean has increased by 8,000 cubic kilometers, or more than 11%. This volume equals the combined annual discharge of the Amazon and Ganges rivers, and could, if it escapes the confines of the Arctic Ocean, affect circulation in the Nordic Seas and the North Atlantic.
Ecosystems are changing. The decline in sea ice thickness and extent, along with changes in the timing of ice melt, are affecting marine ecosystems and biodiversity; changing the ranges of Arctic species; increasing the occurrence of algal blooms; leading to changes in diet among marine mammals; and altering predator-prey relationships, habitat uses, and migration patterns. Terrestrial ecosystems are feeling the effects of changes in precipitation, snow cover, and the frequency or severity of wildfires. The occurence of rain-on-snow and winter thaw/refreezing events affects grazing animals such as caribou, reindeer, and muskoxen by creating an ice barrier over lichens and mosses. While many tundra regions have become greener over the past 30 years, reflecting an increase in plant growth and productivity, recent satellite data show shifts toward browning (indicating a decrease in plant cover and productivity) over large areas of the Arctic, particularly in Eurasia.
Arctic climate trends affect carbon storage and emissions. New estimates indicate that Arctic soils hold about 50% of the world's soil carbon. While thawing permafrost is expected to contribute significantly to future greenhouse gas emissions, the amount released over the past 60 years has been relatively small.
The impacts of Arctic changes reach beyon the Arctic. In addition to the Arctic's role in global sea-level rise and greenhouse gas emissions, the changes underway appear to be affecting weather patterns in lower latitudes, even influencing Southeast Asian monsoons.
Changes will continue through at least mid-century, due to warming already locked into the climate system.
Warming trends will continue. Models project that autumn and winter temperatures in the Arctic will increase to 4-5 degrees C above late-20th century values before mid-century, under either a medium or high greenhouse gas concentration scenario. This is twice the increase projected for the Northern Hemisphere. These increases are locked into the climate system by past emissions and ocean heat storage, and would still occur even if the world were to make drastic near-term cuts in emissions.
The Arctic Ocean may be ice-free sonner than expected. Extrapolations of recent observed data suggest a largely ice-free summer ocean by the late 2030s, which is earlier than projected by most climate models. Natural variability and model limitations make precise predictions impossible.
Declines in snow and permafrost will continue. The duration of snow cover is projected to decrease by an additional 10-20% from current levels over most of the Arctic by mid-century under a high emmisions scenario, and the area of near-surface permafrost is projected to decrease by around 35% under the same scenario.
The melting of land-based ice will contribute significantly to sea-level rise. If increases in greenhouse gas concentrations continue at current rates, the melting of Arctic land-based ice would contribute as estimated 25 centimeters to sea-level rise between 2006 and 2100. Many of the smallest glaciers across the Arctic would disappear entirely by mid-century.
The Arctic water cycle will intensify. Climate models project increases in cold-season precipitation of 30-50% over the Arctic Ocean toward the end of this century, with an increasing portion of that precipitation falling as rain instead of snow.
Arctic ecosystems will face significant stresses and disruptions. Changes in sea ice are expected to affect populations of polar bears, ice-dependent species of seals, and, in some areas, walrus, which rely on sea ice for survival and reproduction. There will also be losses of ice-associated algae. Physical disturbance arising from an increasing frequency of wildfire and abrupt thawing of permafrost could accelerate ecological shifts, such as the expansion of tall shrubs and trees into tundra. Boreal forests will be affected by thawing permafrost, increases in wildfires, insect pest outbreaks, and climate zone shifts.
Arctic changes will affect sources and sinks of important greenhouse gases. The amount of atmospheric carbon dioxide absorbed by the Arctic Ocean may be significantly affected by changes ini sea-ice cover, the structure and functioning of marine ecosystems, and the hydrological cycle. Thawing permafrost is expected to increase emissions of methane.
Substantial cuts in global greenhouse gas emissions now can stabilze impacts after mid-century. However, the Arctic will not return to previous conditions this century under the scenarios considered in this assessment. The near-future Arctic will be a substantially different environment from that of today, and by the end of this century, Arctic warming may exceed thresholds for the stability of sea ice, the Greenland ice sheet, and possibly boreal forest.
The report goes on to suggest adaptation and mitigation strategies and policies.