- Final part of the Polar Ice series.
- First described was the continent of Antarctica to our south followed by the Arctic region to our north.
- This part describes the impact climate change seems to have on each region and their observed trends in behavior.
Studies of the Antarctic continent indicate two significant trends.
• The glaciers flowing toward the sea from the land are speeding up.
• The extent of sea ice surrounding the continent is increasing.
- The continental land mass of Antarctica is huge, 1.4x that of U.S.
- Almost entirely covered by great thick sheets of snow and dense ice.
- Ice slowly flows toward lower elevations at the coastline.
- At the water, the flowing glaciers reach last contact with the bedrock.
- Their flow extends out as a floating shelf onto the sea.
- The ice shelf eventually breaks off, or calves, large iceberg chunks.
- The grounding line recedes farther inland under the glaciers by the melting action of the slightly warmer circumpolar deep water current.
- The receding line allows the glaciers to flow faster toward the sea.
- NASA Earth Observatory reported in May 2014 that several of the major glaciers labeled below in the West Antarctic have accelerated between 1996 and 2008.
- This part of the ice sheet could collapse in a few hundred years and raise sea level by over a meter (3.3 ft).
- NASA published on May 12, 2014 The “Unstable” West Antarctic Ice Sheet: A Primer. It is a good read for more details.
- This video from ScienceCast illustrates the grounding line problem.
- The glaciers are thinning as the grounding line recedes inland.
- This thins the glaciers even more and speeds up their flow.
- It appears nothing will stop this positive feedback process.
- The other significant trend in the Antarctic involves the growth of the sea ice around the continent.
- Records of the recent maximum sea ice extents, and averages from the recent decades, are shown in this chart.
- The 2015 extent in red is on track to continue the trend of recent years.
- This image from September 19, 2014 shows the maximum extent of sea ice.
- The 1981-2010 median extent of sea ice for the date is in orange.
- Growth of the extent can be explained by climate scientists.
- Fresh water increases from glacier melt. Stronger winds away from the continent blow the fresh water out to sea where it freezes.
- It is expected this will be a temporary situation.
- Sea ice will likely decrease in the decades to come due to rising global air temperatures.
- Increase in Antarctic sea ice is only a small fraction of the decrease in sea ice of the Arctic.
- The Antarctic and Arctic trends for sea ice extent are opposite between 1979-2012.
- Antarctic region shows slow increase of the dotted red line.
- Arctic shows greater decrease by the steeper dotted blue line.
- The overall trend is toward less total sea ice at the poles of the Earth.
- Minimum extent of Arctic sea ice occurs in September each year.
- Three recent years had significantly less sea ice at minimum.
- The 2015 extent in red is on track to continue that trend.
- Video of 1979-2014 minimum extent of ice at the end of Arctic summer.
- Minimum extent decreased rather dramatically after 2000.
- Submarine records from 1958-2000 and five years of ICESat satellite records from 2003-2008 show the mean Arctic sea ice thickness declined from 3.64 meters in 1980 to 1.89 meters in 2008.
- That is a decline of 1.75 meters … nearly 50%.
- Greenhouse gas emissions from fossil fuel use is the most likely cause of the global temperature increases responsible for sea ice melting.
- Complicating factors are the Arctic Oscillation in the north Atlantic region and the El Niño in the Pacific.
- Thicker sea ice tends to carry annual layers of white snow on top.
- Snow is highly reflective and insulates the layers of snow and ice below from the sun’s heat.
- It also insulates the dark waters below allowing them to remain cold.
- In the late 1990s, coasts of Alaska and Siberia had significant sea ice melting.
- The next winter freeze and recovery didn’t happen as much as expected.
- By the mid-2000s, the sea ice had still not recovered to historical values.
- In 2007-2008, snowfall was sparse over the Arctic allowing more sunlight and heat to penetrate deeper.
- More of the darker waters were exposed to the warmth of the sun during the summer months.
- In 2012, sea ice extent reached a minimum record.
- The extent in 2013 still well below the historical average.
Greenland Ice Features
- During the 7th spring campaign of Operation IceBridge, scientists and crew flew over northern Greenland’s Ryder Glacier.
- The flight of May 6, 2015, revealed this large moulin in the glacier.
- A moulin is a hole where melt water drains to the bottom of the glacier or out to sea.
- Not much melting had occurred yet near this one.
- After summer melting, water flows into the moulins and disappears.
- Scientists give us a view of this activity from a small drone aircraft.
- The dark markings are caused by microbes growing on the ice.
- Another feature of the Greenland glaciers is crevassing.
- Crevasses are stretch marks on the ice formed because the ice accelerates as it flows toward the coast.
- Crevasses are also prominent in the Antarctic glaciers.
- The acceleration is likely aided by the large amounts of melt water flowing down the moulins under the glaciers.
Prospects For The Future
In the Arctic…
- Global warming and wind patterns are the main drivers of sea ice decline since the late 1990s. It may not be able to recover.
- We may have passed a tipping point. There may be an Arctic ice-free during at least part of the late summers in the future. There is not general agreement when it will occur.
- Long-term records dating back to the 1950s show that spring melts have started earlier and continued longer into the year.
- Actual Arctic sea ice decline, when compared to model projections, show it faster than any of the models have predicted.
In the Antarctic…
- Stronger westerly winds are resulting in more sea ice. Evidence suggests these winds are in response to climate change from CO2 and other greenhouse gas increases. (Thompson and Solomon, 2002; Thompson et al., 2011). The evidence points to human impact in origin, but for different reasons than in the Arctic.
- The average increase of relatively thin Antarctic sea ice is a small number by mass. Scientists have observed rapid declines of the larger and thicker Bellingshausen and Amundsen Seas, comparable to sea ice declines in the Arctic. Antarctic sea ice loss will likely take place in the future.
- The time scale for significant sea level rise may take several decades up to a century. This is also the time scale for human efforts to mitigate or reverse the effects.
- This should be a topic of more widespread discussion in all societies of the world. A significant fraction of the world population lives near the oceans.
On June 18, 2015, JPL released this lecture by Dr. Ron Kwok Senior Research Scientist about sea ice in the Arctic and Antarctic. It is just over an hour in length.