The Earth’s two poles - the Arctic and Antarctic - are so cold that for much of the year, even seawater freezes. Floating on the ocean, the enormous expanse of sea ice is at its maximum extent in winter, and melts to its minimum in late summer.
Sea ice provides a solid home for penguins and polar bears that can be many feet thick. Other animals live on, around, and under the ice. In fact, animals of the ice all depend on it in one way or another.
Sea ice also plays a major role in the Earth's global system. It keeps the polar regions cool, and moderates weather and climate all over the world.
But the steady climate we’ve enjoyed over the last 10,000 years is changing and our warming world is melting polar ice at an alarming rate. Less ice cover allows more of the Sun's energy to reach the ocean and warm it's upper layers. A warmer Arctic Ocean could lead to changes in atmospheric and ocean circulation.
Since we began measuring with satellites in 1979, the summer minimum area of Arctic sea ice has shrunk by nearly 50%.
The 10 lowest extents have all happened within the last 11 years and 2016 was especially warm, and was tied for the second lowest area ever.
So why is the sea ice shrinking?
Arctic sea ice is melting at an alarming rate because ocean and air temperatures are getting warmer. Here’s how:
The burning of fossil fuels emits carbon dioxide and other heat-trapping gases into the atmosphere.
The heat absorbed by these gases is radiated back towards the Earth’s surface. Then the ocean absorbs this heat from the air. As the ocean heats up, sea ice melts A newer discovery is that, even if sea ice area is the same year to year, sea ice thickness, or volume, is shrinking. This is because the warm water melts sea ice from underneath, a little bit more every year. So sea ice volume is shrinking too. In 2016, sea ice volume hit an all-time record low.
If we are to understand how much and how fast the ice is melting, we need to be able to accurately measure it.