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  • Writer's pictureZarrin Tasneem

The Importance of Sea Ice Classification in Understanding Climate Change.

Modis Image was used with the concept of NDSI



What is NDSI?


NDSI - Normalized Differential Snow Index



The Normalized Difference Snow Index (NDSI) snow cover is an index that is associated with the existence of snow within a pixel. 



Snow usually has a very high visible (VIS) reflectance and very low reflectance in the shortwave infrared (SWIR), which is a characteristic utilized to identify snow by differentiating between snow and most cloud types. Snow cover is found by utilizing the NDSI ratio of the difference in VIS and SWIR reflectance



NDSI = ((band 4-band 6) / (band 4 + band 6))



A pixel with NDSI > 0.0 is known to have some presence of snow



A pixel with NDSI <= 0.0 is a snow free land surface (Riggs et al., 2016).




Blue, and red ice are considered as the different types of ice formations, each with unique characteristics associated with their formation, age, and the environmental conditions around them.


  1. Blue Ice:

  • Formation: Takes place when snow falls on a glacier, and it becomes compressed, eventually absorbing into the glacier. Over the years, air bubbles are squeezed out, and ice crystals become large, enabling the change in the color of the ice to blue.

  • Reason for Color: The blue color is formed due to the absorption of red light within the ice at longer wavelengths and the scattering and transmission of light at the blue end of the spectrum. Therefore, larger quantity of blue light is being transmitted and scattered than red light, providing the ice with a distinct blue color.

  • Location: Blue ice is normally found in the cores of glaciers and in locations of ice caps where there is minimal snow. It is also recurrent in locations where glaciers move into warmer regions and initiate the melting process.

  • Significance: Locations where there are blue ice usually supply important clues regarding the history and composition of glaciers. They are also used in scientific studies, such as ice core drilling, to understand climate change.

  1. Red Ice (White Ice):

  • "White ice" in the context of glaciology and sea ice studies typically refers to a type of ice that has a high concentration of air bubbles, which gives it a white appearance. This is in contrast to "blue ice," which appears blue because it has fewer air bubbles and thus allows deeper penetration of light. Here are some key characteristics of white ice:

  1. Formation: White ice forms when snow falls on ice and gets compacted. As more snow layers accumulate and compress, the lower layers turn into ice. During this process, tiny air bubbles get trapped within the ice.

  2. Air Bubbles: The high concentration of air bubbles in white ice is what makes it appear white. Light entering the ice scatters in all directions because of these air bubbles. Since all wavelengths of light scatter equally, the ice appears white, which is the color that results from the combination of all colors of light.

  3. Reflectivity (Albedo): White ice has a high albedo, meaning it reflects a large percentage of the sunlight that hits it. This is an important factor in climate studies, as the high reflectivity of ice affects local and global temperatures.

  4. Occurrence: White ice is commonly found in snowy environments, like the polar regions, and on the surfaces of glaciers and ice sheets.

  5. Significance: The presence of white ice, with its high reflectivity, plays a crucial role in Earth’s climate system. It reflects sunlight back into space, which helps regulate the planet's temperature. The decreasing extent of white ice due to melting (as a result of global warming) is a concern in climate change studies because it leads to lower albedo and further warming.

Figure 1 - The Whole Map of Red, and Blue Ice


Figure 1 - The Whole Map of Red, and Blue Ice, including antarctica


Sea ice classification plays an important role in understanding and addressing climate change because of many crucial reasons:

  1. Indicator of Climate Health: Sea ice is a responsive indicator of changes in the Earth's climate. As the climate warms, sea ice melts; alternatively, in cooler climates, it expands. Monitoring the patterns of sea ice aid scientists in gauging the rate and extent of climate change.

  2. Impact on Global Temperatures: Sea ice impacts the Earth's albedo, which is the ability to reflect sunlight. Ice has a high albedo and reflects most of the sun's energy back into space. As sea ice disappears, darker ocean waters absorb more heat, further warming the planet—a phenomenon known as the ice-albedo feedback.

  3. Ocean Circulation and Weather Patterns: Sea ice formation and melting affect ocean circulation, which impacts global climate and weather patterns. For example, the salinity and temperature of ocean waters are altered by the presence or absence of sea ice, affecting ocean currents such as the thermohaline circulation.

  4. Ecosystem Health: The existence and extent of sea ice are important for marine ecosystems. Many species, such as polar bears and seals, depend on sea ice for hunting and breeding grounds. Changes in sea ice cover can significantly impact these species' survival and the overall health of the Arctic and Antarctic ecosystems.

  5. Sea Level Rise: While sea ice melting does not directly contribute to sea level rise (since it's already floating), the loss of ice shelves can speed up the flow of glaciers and ice sheets into the ocean, which does contribute to rising sea levels.

  6. Data for Predictive Models: Accurate classification and monitoring of sea ice help improve the models that predict future climate scenarios. These models are crucial for developing strategies to mitigate and adapt to climate change impacts.

In summary, sea ice classification is integral to our understanding of climate change's dynamics and implications, helping to inform both scientific research and policy decisions.

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