What will happen if melting sea ice reaches a tipping point?
By Michael Coppola and Nancy Lazar
Sea Ice- what is it and how it works
Sea ice is a combination of frozen salt water and accumulated ice from snow fall. It does not play much of a direct role in the raising of sea level when it melts, because the major component comes from the sea water freezing. The smaller component from the accumulation of snow over the years will add water to the seas but it does not result in a significant rise in sea level. That means during the warmer months melting sea ice is similar to an ice cube melting in a glass of water where the amount of volume stays the same. However, scientists measure the extent of sea ice at the poles every day. That important data provides a look into a serious problem for our planet.
A combination of land and sea ice has
kept the planet from overheating for thousands of years. Sea ice along with the
continental ice sheets that cover the land masses at the poles provides “air
conditioning” cooling the atmosphere for the planet.
Although the total amount of sea ice has only reduced by about five percent
each decade for the past 20 years, the percent of old ice has reduced
dramatically. With warmer winters less ice is formed; with hotter summers more
ice melts. Older multi-year ice has been melting more each year as compared to
the period from 1981 to 2000. This is a serious problem. As explained by scientist
at the National Snow and Ice Data Center (NSIDC), “When ice first forms it is dark gray
because the color of the ocean still comes through (i.e., the light penetrates
through the ice and reflects off the low albedo [low reflectivity] ocean water
below). As it thickens, it gets lighter gray and then towards white as less
light penetrates to the ocean below and the ice becomes the main reflector
(high albedo). “
New ice and older ice has other differences. “Thinner seasonal or first-year ice - ice that hasn’t survived a summer - is thinner and flatter and melt water that pools into melt ponds, is darker and more spread out. The older, multi-year ice - ice that has survived at least one summer - is thicker and also more broken up - more “hills” and troughs.” This allows for fewer pools of water leaving more of the higher albedo ice, “
Sea ice plays a critical role in the ocean's currents. The circulation of warm waters from the equator is critical to the maintenance of both air and water currents. See our article on the AMOC, for a more in-depth description of ocean and air circulation.
The mechanism that drives the ocean currents is the difference in temperature and salinity of the waters in the northern latitudes and equatorial latitudes. Both the temperature and the salinity of the water determine its density. Under current climate conditions the ocean circulation brings warm salt water from the equator to the northern latitudes. When it reaches the northern latitudes it cools and becomes denser and sinks deep below the surface and maintains a slow steady convection cell that returns the water to the equator via deep water. During the winter when ice forms, the salinity of the sea water increases, making it more dense, because when salt water freezes the salt is driven out of the ice and into the sea water. If less ice forms during the winter, the water does not become salty enough to sink at its normal rate. This disrupts or slows down the ocean circulation.
To a lesser extent but still adding to the problem, if during the summer too much sea ice melts adding larger amounts of fresh water to the sea it becomes less saline and less dense inhibiting the sinking. A slowing of the ocean currents affects both the life in the sea as well as on land.
Sea ice also plays an important role in slowing the flow of
continental ice sheets into the oceans.
The data on sea ice formation shows a drastic change is occurring
Satellite data on the amount of sea ice covering the seas at both poles began in 1981. The National Snow and Ice Data Center (NSIDC) is one organization that collates data daily on sea ice, interprets it and provides the data to scientists worldwide for climate research. Field visits are also made by ships and planes to verify the data from the satellites as well as gather information that is not provided by remote sensing. They also publish a monthly report on sea ice conditions and show this data on several graphs. By overlying this data on a grid of the seas the scientists determine what percentage of the area is covered by ice.
To show the extent of sea ice for both the
As each year after 2010 is plotted we get to see if the ice production is within the same range for the 39 year period. If the planet is remaining stable then we would expect to see the lines for 2011 to the present year falling on or around the median line and within the two statistical ranges. If these lines fall outside the statistical range then we can see how the creation of sea ice is changing.
A sample of the graph of the amount of ice cover vs. calendar days for December is shown below:
The blue line shows the current year's ice extent. The dashed line represents the record low year to date which is 2012. The dark gray line is the median. The lighter shaded area is the interdecile range and the darker shaded area is the interquartile range.
Scientists have reason to be concerned when a new
record low of ice occurs. To see how the amount of sea ice is trending
for the
As can be seen on the graph the amount of sea
ice for all five years was well below the median and below the interquartile
and the interdecile ranges, which means there has been a steady increase in the
loss of ice. The current year’s plot, the blue line, shows that we are headed
for a new record low in sea ice, which was set in 2012. Each time less ice is
created during the winter season it means there is less ice at the start of the
summer melt season. This results in a period of time where there is more dark
water to absorb the strong sunlight of the summer. This drives the feedback
loop of the melting of older ice and we have a vicious cycle of constantly
decreasing sea ice.
If this trend continues no further increase in greenhouse gases into the atmosphere would be needed to continue the steady decrease in sea ice until all the ice is gone. This trend is moving us toward the tipping point. In order to prevent this we need to do two things. One, stop putting greenhouse gases into the atmosphere, and two either remove greenhouse gases from the atmosphere or reduce the amount of long wave radiation going into the atmosphere by increasing the reflectivity of the planet’s surface. Which means, we should cut back on our use of fossil fuels, cut back on meat production to reduce methane, plant trees to help absorb more carbon, and change as many reflecting surfaces as possible from dark colors to light.
References
Environment : Climate | National Snow and Ice Data Center (nsidc.org)
Arctic Sea Ice News and Analysis | Sea ice data updated daily with one-day lag (nsidc.org)
What are Tipping Points in the Climate Crisis? | Earth.Org - Past | Present | Future
As Climate Change Worsens, A Cascade of Tipping Points Looms - Yale E360
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