The winter ice covering the Arctic Ocean has reached its annual peak, but the extent of sea ice this winter is smaller than it has been since scientists began keeping consistent satellite records. (New York Times graphic)
Teachers, scroll down for a quick list of key resources in our Teachers’ Toolkit.
- Scientists recently tracked the extent of Arctic sea ice. What is sea ice? How is it different from regular ice?
- Sea ice is just what it sounds like—frozen ocean water. According to the good folks at the National Snow & Ice Data Center, sea ice “forms, grows, and melts in the ocean. This makes it different from icebergs, glaciers, ice sheets, and ice shelves, which all originate on land.” Both Arctic and Antarctic regions have sea ice.
- New data show Arctic sea ice has reached its lowest “winter maximum” on record. What is a winter maximum? In what months do you think sea ice experiences a winter maximum?
- A winter maximum is also just what it sounds like. Sea ice grows and reaches its maximum extent during cold Arctic and Antarctic winters.
- The months when sea ice reaches a winter maximum depends on what hemisphere you’re in.
- In the Northern Hemisphere, Arctic sea ice usually reaches its maximum extent in the middle of March. (This year, it reached its maximum in late February.)
- In the Southern Hemisphere, Antarctic sea ice usually reaches its maximum extent in late September. (The extent of Antarctic sea ice, by the way, is actually increasing.)
- Look at our great map about the slow withdrawal of Arctic sea ice. The map, however, focuses not on “winter maximums,” but on “summer minimums.” What is a summer minimum?
- The summer minimum is when, warmed by the summer sun, sea ice recedes to its lowest point. Summer minimums are increasing—meaning less ice—with some experts predicting an ice-free Arctic Ocean by 2030.
- The NY Times graphic reports that “Summer minimums . . . can have a greater effect on the global climate than winter maximums.” Why? Take a look at the top of our “Twilight of the Arctic Ice” map for some help.
- A climate “feedback loop” contributes to a greater loss of sea ice. According to NASA scientist Walt Meier, “During the relatively sunny summers, the dark ocean surface of ice-free parts of the Arctic absorbs much more solar energy than highly reflective sea ice. This can create a warming feedback loop when the ocean absorbs sunlight and heats the air above it.”
- The ice that melts during summer minimum is older, thicker ice. “When you lose summer ice you aren’t really just losing it for that year, you’re also losing some ice from many years ago,” he said. “That makes it harder for things to go back towards normal.”
New York Times: Arctic Ice Reaches a Low Winter Maximum
National Snow and Ice Data Center: Arctic sea ice reaches lowest maximum extent on record
Nat Geo: Polar Regions MapMaker Kit
National Snow and Ice Data Center: All About Sea Ice
Nat Geo: Twilight of the Arctic Ice