Ocean Decline

Disappearing Sea Ice: Why It Matters

In the Arctic, temperature has increased at twice the rate as the rest of the globe, and could increase by another 8°C (14°F) by the end of this century. The increased rate is caused when shrinking sea ice allows more sunlight to be absorbed, leading to an increasing rate of local warming. The warming atmosphere along with new weather pattern extremes is causing Arctic sea ice to melt at an alarming rate. Recent data suggests summer ice will be entirely gone by 2015, fifteen years earlier than more recent forecasts. The impacts of dwindling ice cover in the Arctic are far-reaching, from species endangerment (as reported in this blog) to enhanced global warming, to the weakening or shut-down of global ocean circulation.

Sea Ice and the Climate System

Sea ice forms and melts in sea water, as opposed to land-based ice such as glaciers, ice sheets or shelves, and grounded icebergs. In today's climate regime, sea ice has been observed as far south as Bohai Bay in China—a latitude comparable to the Mediterranean Sea. Sea ice begins to form when water temperature dips just below freezing. It grows into small sheets that look like pancakes, and eventually merge together to form large ice floes which can span miles. As the ice forms, it expels the salt, which increases the density of the surrounding water and thus plays a critical role in global ocean circulation.

Temperature in the Arctic has increased at twice the rate as the rest of the globe. Increases are expected to throughout this century as a result of continued release of greenhouse gases, especially carbon dioxide. Winter temperature has increased more than summer temperature, a trend that is also expected to continue. While some have suggested that these variations in temperature and associated sea ice melt are a natural cycle, recent research tells us that the Arctic was in a 2,000 year cooling trend before the influence of greenhouse gases in the 20th century.

Bright white sea ice reflects almost all of the incoming solar radiation back to space, whereas the dark ocean surface absorbs nearly all of it. Image source: Stephen Hudson / Norsk Polarinstitutt.

Sea ice is generally moderated by sunlight—it grows in the winter and melts in the summer—but there are other factors at play in the decline of ice in the Arctic Ocean. Warm ocean currents travel north from the equator, ushering warmer water and making sea ice growth difficult. Weather patterns over the high mid-latitudes and the Arctic can also affect sea ice growth. Under normal climate conditions, cold air is confined to the Arctic by the polar vortex winds that circle counter-clockwise around the North Pole. As sea ice coverage decreases, the Arctic warms, high pressure builds, and the polar vortex weakens, sending cold air spilling southward into the mid-latitudes, bringing record cold and fierce snowstorms. At the same time, warm air will flow into the Arctic to replace the cold air spilling south, accelerating sea ice loss and leading to 'runaway' regional climate change.

The primary role that sea ice plays in global climate its ability to efficiently reflect the Sun's radiation. This property is called "albedo," the measure of the reflecting power of a surface. The albedo of snow-covered sea ice is 0.90, meaning it reflects 90% of the Sun's radiation. Just like wearing a white shirt will keep you cool when you're out in the Sun, sea ice covering the Arctic keeps the thermostat low. The ocean surface, however, is almost black, absorbing 90% of the incident light and reflecting only 10%.. After something absorbs sunlight, it emits heat. This means that warming ocean waters will also accelerate the loss of sea ice.


Observed Sea Ice Melt

Satellite data show that since the late 1970s, September Arctic sea ice extent has decreased by about 11% per decade. What's especially alarming is the decrease in multi-year ice. Sea ice is classified by age, usually as "new ice" or "multi-year" ice (meaning it survived many summer melting seasons). While new ice is very shallow, multi-year ice can grow to be quite thick, typically between 6 and 12 feet, and is very stable. A remarkable study was published in 2007 which measured the amount of multi-year ice in the Arctic. In 1987, 57% of the observed ice pack was at least 5 years old, and around 25% of it was at least 9 years old. When they surveyed the Arctic again in 2007, only 7% of the ice pack was at least 5 years old, and the ice that was at least 9 years old had all but vanished. Likewise, sea ice thickness and volume have decreased markedly since the beginning of the satellite era.

Sea ice volume observations from PIOMAS (blue) and a simple mathematical function (orange)
to fit the data and produce a forecast, suggesting the Arctic would be ice-free by the year 2030.
Recent data (below) shows a more dramatic loss.



Recent years have set a number of sea ice records in the Arctic. The summer of 2007 saw a "perfect storm" of weather conditions favorable for ice loss. Unusually strong high pressure over the Arctic led to clear skies and plenty of sunshine. The polar vortex weakened, injecting large amounts of warm air into the Arctic. Sea ice loss doubled to 39% in 2007, according to the National Snow and Ice Data Center. In one year, as much ice was lost as in the previous 28 years combined. In 2011, the University of Bremen reported that sea ice had reached a new all-time low on September 8th, and was 27,000 square kilometers below the previous record set in 2007.





PIOMAS graphs were updated this past summer, showing that sea ice volume was at an all-time
low in August, 2011. Models now predict a complete disappearance of summer sea ice by 2015.

   
Commercial Traffic

Recent low sea ice levels have provided new opportunities for the shipping industry, opening both the Northeast and the Northwest Passages in the Arctic Ocean. The Northeast Passage is a shipping route that runs along the northern Russian coast and to the Bering Strait, sometimes called the "Northern Sea Route." On the other side of the Arctic Ocean, the Northwest Passage runs along the North American coast through waterways in the Canadian Arctic Archipelago. These passages have been elusive since the early 1900s, although climate change has recently freed up both of the typically ice-choked routes. The Northeast Passage opened for the first time in recorded history in 2005, and the Northwest Passage in 2007. For four years in a row, the Northwest Passage was open for ice-free sailing. It now appears that the opening of one or both of these northern passages is the new norm, and business interests are taking note—commercial shipping in the Arctic is on the increase, and there is increasing interest in oil drilling. The great polar explorers of past centuries would be astounded at how the Arctic has changed in the 21st century.

The Forecast



Sea ice extent observations (1970 to 2007) and forecast (2030 to 2100) reproduced using data
from the NOAA GFDL model. Yearly extent represents an average 80% sea ice concentration.
Click on the image for a larger view.

Scientists use numerical models to predict how fast Arctic sea ice is expected to melt in coming decades. So far, these climate models have done a poor job predicting the recent record loss of Arctic sea ice. None of the models used in the 2007 Intergovernmental Panel on Climate Change (IPCC) report have foreseen the recent, remarkable sea ice loss. This is likely because the models have a hard time understanding the transport of heat within the ocean itself, which some argue causes over 50% of Arctic sea ice loss.

The prevailing view among climate scientists had been that an entirely ice-free Arctic ocean would occur in the 2070 - 2100 time frame. The February 2007 report from the IPCC warned that without drastic changes in greenhouse gas emissions, Arctic sea ice will "almost entirely" disappear by the end of the century. However, recent observations suggest that a complete loss of summer Arctic sea ice could occur much earlier. Using a simple equation to produce a forecast from the observations, we can now see that the Arctic could be entirely ice free by 2030 and this hypothesis is supported by numerous scientists and organizations. Dr. Wieslaw Maslowski and his team from the Naval Postgraduate School in Monterey, California have a model that predicts that increasing summer sea ice melt could lead to an ice-free Arctic during at least part of the northern hemisphere summer by 2016, with a margin of error of plus or minus three years.

Impacts of Disappearing Sea Ice

The impacts of an ice-free Arctic are far-reaching, and could be a trigger for abrupt, cataclysmic climate change in the future. Although it is difficult to see exactly how sea ice decline will impact the local and global environment, basic understanding of the Arctic as well as recent observations give us a good idea of how things might change.

Sea level rise

Direct effect: The melting of the Arctic sea ice will not change ocean sea levels appreciably, since the ice is already floating in the ocean. Sea ice melting does slightly contribute to sea level rise since the fresh melt water is less dense than the salty ocean water it displaces. According to Dr. Robert Grumbine of NOAA's sea ice group, if all the world's sea ice melted, it would contribute to about 4 millimeters of global sea level rise. This is a tiny figure compared to the 20 feet of potential sea level rise locked up in the ice of the Greenland Ice Sheet, which is on land.

Indirect effect: The biggest concern regarding Arctic sea ice loss is the warmer average temperatures it will bring to the Arctic in coming years. Warmer temperatures will accelerate the melting of the Greenland ice sheet, which holds enough water to raise sea level 20 feet. Although the IPCC's 2007 report predicted only a 0.6-1.9 foot sea level rise by 2100 due to melting of the Greenland ice sheet and other factors, these estimates will probably need to be revised upwards in light of unexpectedly high sea ice loss in the Arctic.

Weather patterns

Continued loss of Arctic sea ice may dramatically alter global weather and precipitation patterns in the decades to come. The jet stream will probably move further north in response to warmer temperatures over the pole, which will bring more precipitation to the Arctic. More frequent and intense droughts over the U.S. and other regions of the mid-latitudes may result from this shift in the jet stream. Changes to the course of the jet stream affect weather patterns for the entire planet, and we can expect impacts on the strength of the monsoons and recurvature likelihood of hurricanes. During 1979 to 2006, years that had unusually low summertime Arctic sea ice also had a 10-20% reduction in the temperature difference between the Equator and the North Pole. This resulted in reduced winter precipitation over all of the U.S., Alaska, and Northern Europe. In contrast, increased precipitation fell over Spain, Italy, and Japan during these winters. Although intense La Niña or El Niño events can have a much stronger influence on wintertime weather patterns, reduced summertime Arctic sea ice should give most of the Northern Hemisphere a delayed start to winter during most years for the foreseeable future.

Global ocean circulation

Surface global ocean currents are driven by the winds, but the vertical ocean circulation is determined by the temperature and salt content of the water (hence, is called the thermohaline circulation). The engine of the thermohaline circulation is in the North Atlantic, where warm surface waters travel north past Greenland and into the Arctic on the Gulf Stream current. As the warm water reaches cold air, evaporation cools the water, and sea ice formation increases the salinity (salt content) of the surrounding water (ice rejects the salt as it freezes). This new cold, salty water is very dense, and sinks in a process called overturning. This sinking motion in the Arctic is a driving force behind the "global conveyor belt," and the formation and maintenance of sea ice is a the heart of it all. Not only could the slowdown of new sea ice formation lead to the abatement of the thermohaline circulation, but as sea ice melts, it injects massive quantities of freshwater into the Arctic Ocean. The freshening of Arctic sea water due to manmade climate change could lead to exceptional changes in the world's ocean circulation and thus Earth's climate as well.

Methane

Sea ice loss is correlated with warming of Northern latitudes. This has melting effects on permafrost, both in the sea and on land. Current rapid melting of the sea ice induces a rapid melting of arctic permafrost. This has consequential effects on methane release and on ecosystems. Studies also predict cold air passing over ice will be replaced by warm air passing over the sea. This warm air carries heat to the permafrost around the Arctic and melts it. This thawing permafrost then releases huge quantities of methane. Methane release can be gaseous, but is can also be transported in solution by rivers.

Methane has a 20:1 greenhouse gas ratio, compared to carbon dioxide.
This means one unit of methane is equivalent to 20 units of CO2.

NewScientist states that "Since existing models do not include feedback effects such as the heat generated by decomposition, the permafrost could melt far faster than generally thought."

Methane arises from destabilization of gas hydrates concentrated along the coastal margins of Arctic land masses such as Alaska, Siberia, Canada and Greenland.

Area in northern Alaska where subsurface temperature and pressure conditions are conducive
to the occurrence of gas hydrates (red outline), compiled for USGS Fact Sheet 2008-3073.
Note that gas hydrate could occur in sediments both onshore and at shallow water depths
offshore. TPS: Total Petroleum System.

Hydrates are ice-like crystalline solids formed from a mixture of water and natural gas, most commonly methane. Gas hydrates are stable at moderate pressures and low temperatures and are widespread in:

• continental-margin sediments at greater than 300-m water depth, and
• areas of continuous permafrost onshore and relict permafrost in the shallow offshore (less than 100-m water depth).

Globally, gas hydrate sequesters huge amounts of methane, which is known to be a far more potent greenhouse gas than CO₂. Climate perturbations could destabilize gas hydrate deposits and potentially release substantial amounts of methane to the atmosphere.

Research from the Monterey Bay Aquarium Research Institute suggests that 'Pingo' mounds at the floor of the Arctic ocean may have a cause that could contribute dramatically to climate change by adding the super greenhouse gas methane to the atmosphere.



Conceptual drawing (not to scale) shows the hypothesis that methane gas from deep
hydrate deposits could push sediment up from below the ocean bottom to create a
pingo-like feature. The gray lines in the background are from a seismic profile through
one of these enigmatic features. Image:MBARI 2007

Ecosystems



Polar bears and other Arctic mammals use sea ice as hunting platforms,
and are particularly susceptible to climate change.

Sea ice is important in marine ecosystems in at least three ways. First, it provides a habitat for algae and invertebrates and fish, and regulates the temperature of the water below it. Although it seems counterintuitive, the sea ice insulates the water beneath it, keeping it from becoming too cold. Second, as the ice melts in the summer, it releases the organisms into the water, providing fuel for Arctic marine food webs. Finally, it provides breeding and hunting grounds for marine mammals and birds that call the North their home.

The impacts of melting ice extend well beyond polar bears. Birds, seals, and whales also use the ice for hunting. Birds nest in the sea ice and use it for protection while raising their young in the potentially deadly environment of the Arctic. The retreat of sea ice, especially in the warm winter months, has decreased the available platforms that seals, walruses, and polar bears use to rest on and hunt from. Scientists estimate that retreating sea ice will result in a loss of 2/3 of the polar bear population, and force the remaining bears into a smaller, iceless area.

Because ecosystems are globally interconnected and interdependent, the collapse of the Artic ecosystem will have far reaching implications for other parts of the world.