Did you know that scientists monitor climate change through the measure of sea ice that covers the Arctic Ocean at a given time?

Sea ice reflects sunlight back into space, regulating ocean and air temperature alongside circulating ocean water and maintaining animal habitats. NASA and the National Snow and Ice Data Center in Boulder, Colorado, use satellites to observe sea ice extent.

Arctic sea ice extent has observed to be steeply declining year-round over the past several decades, especially in late summer. It forms in the cold winter months, when seawater freezes into massive blocks of floating ice, then partially melts away in the warm summer months. This cycle repeats itself every year.

Here are some interesting facts about sea ice shared by NASA.

1. Sea Ice Extent is Declining

NASA has tracked minimum and maximum extents of sea ice since 1978. While the exact extent figures may vary year to year, the overall trend is clear: the Arctic is losing its ice year-round.

The last 15 years, we’ve seen the lowest 15 sea ice minimum extents, says Dr. Rachel Tilling, a sea ice scientist at the University of Maryland and NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

Arctic sea ice minimum extent is now declining at a rate of 13.1% per decade. The pace is likely to accelerate because of climate change-induced warming and the ice-albedo feedback cycle. The albedo effect describes the white ice surface’s ability to reflect Earth-bound sunlight back to space. Redirecting solar energy away from the ocean keeps the seawater beneath the ice cooler. When this ice melts, darker-colored liquid water is left exposed to absorb sunlight. That warmer water then melts additional ice, creating the ice-albedo feedback cycle.

2. Sea Ice Helps Prevent Atmospheric Warming

Sea ice acts as a ‘blanket’, separating the ocean from the atmosphere. In addition to keeping sunlight out, it traps existing heat in the ocean, keeping it from warming the air above.

Every year, some ice survives the summer melt. Once winter hits, more water freezes and it becomes thicker and stronger “multiyear ice.” First-year ice is thinner and more likely to melt, fracture, or even be swept out of the Arctic.

With more ice melting every year, there is less recurring, multi-year ice. As a result, Arctic sea ice is as young and thin as it has ever been, making it a less efficient blanket.

3. Sea Ice Affects Arctic Wildlife Above and Below Water

Sea ice is a huge ecosystem of water. As sea ice declines, animals such as arctic foxes, polar bears and seals lose their habitat and there are adverse effects beneath the ice’s surface, too.

As ice crystals form atop seawater, they leave behind salt in the ocean below. This dense, salty water can sink to the bottom of the ocean. The descending water in one location will be offset by rising motion in others, which results in more nutrient-dense water circulating up toward the surface.

Those nutrients are essential to microscopic phytoplankton, which are then eaten by fish and animals. The regular melt-freeze cycle keeps underwater Arctic life thriving, from algae to killer whales.

4. Sea Ice Melt Does Not Greatly Contribute to Sea Level Rise

Because sea ice forms from the seawater it floats on, it behaves much like an ice cube in a glass of water. Like that ice cube, which does not change the water level of the glass when it melts, melting sea ice in the Arctic does not dramatically change sea level.

Melting land ice, for example from the Greenland or Antarctic ice sheets, does contributes to sea level rise. That’s because when land ice melts, it releases water that was previously trapped on land and adds to the water in the oceans.

5. Satellites Allow NASA to Monitor Sea Ice

The Arctic Ocean is a difficult place to access and study. Two types of instruments are generally used to monitor sea ice.

The first type are passive microwave instruments, which track extent over time. A series of these instruments aboard satellites supported by NASA, NOAA, the U.S. Department of Defense, and international partners, have monitored arctic sea ice extent since 1978 – more than 40 years.

The second type are altimetry instruments, which can be used to estimate sea ice thickness. NASA’s Ice, Cloud and land Elevation Satellite-2 (ICESat-2), launched in 2018, uses a laser to measure the height of the ice and the height of the water. Using the known relationships between the two measurements (what height of ice above the water’s surface corresponds to the depth of the ice below it), scientists can calculate its total thickness.

Also read: The most sobering report card yet on climate change and Earth’s future

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