GEOGRAPHY

While discussing his new plan to combat global warming, President Obama referenced one of the most striking shifts in the history of National Geographic maps. (Nat Geo News)

Learn more about the “Twilight of the Arctic Ice” with our beautiful map. (Download the full-size version here.)

Teachers, scroll down for a quick list of key resources in our Teachers’ Toolkit.

Note: Current Event Connections is slowing down for the summer. Our column will continue to appear once or twice a week until mid-August. If you have an idea for a Current Event Connection, a recommendation for a good read, or want to share one of your MapMaker Interactive maps, let us know in the comments!

Discussion Ideas

• According to Nat Geo News, “Ice loss is accelerated in the Arctic because of a phenomenon known as the feedback loop.” How does the feedback loop work? Take a look at the graphic above for some help.
  • Fact: Thin ice reflects less sunlight than thick ice. Thick, snow-covered ice reflects about 85% of sunlight, while the open ocean reflects as little as 7%. This provides a “feedback loop” in which a warm ocean gets warmer.
    • Feedback Loop 1: The less sunlight is reflected, the more heat the ocean absorbs. A warmer ocean weakens the ice above—causing it to thin and warm the ocean even more.
    • Feedback Loop 2: Because thinner ice is flatter, it allows melt ponds to accumulate on the surface, and liquid water is much less reflective than solid ice or snow. This allows the ice to weaken and thin—and warm the ocean even more.

• The great Nat Geo maps of the Arctic actually show the extent of two ice fields: multiyear ice and sea ice. What is the difference between multiyear ice and sea ice? How are they depicted differently in Nat Geo maps?
  • Multiyear ice is older—in fact, another name for multiyear ice is simply “old ice.” Multiyear ice is displayed as a white mass on Nat Geo maps.
  • Sea ice freezes and melts seasonally—its extent grows in the winter and shrinks in the summer. Sea ice is depicted as a line or lines on Nat Geo maps. The map above, for instance, displays the extent of two measures of sea ice. The blue line displays the extent of sea ice in September 1980, while the orange line displays the extent of sea ice in September 2007.

• How does melting Arctic ice contribute to sea level rise?
  • It doesn’t! At least, not directly. Ice that’s floating in the ocean can’t raise sea levels when it melts. Its volume is simply distributed differently (as a liquid instead of a solid).
  • However . . . as the exposed ocean absorbs more sunlight, the entire Arctic region will keep heating up. And that’s important when it comes to the vast ice sheet covering Greenland. The melting of the Greenland ice sheet—all 2.85 million cubic kilometers (683,751 cubic miles) of it—could definitely raise sea levels. In fact, sea levels are on pace to rise at least .3 meter (a foot) by 2050, and possibly a meter (3 feet) by 2100.

TEACHERS’ TOOLKIT

Nat Geo: Yes, Mr. President, We Remade Our Atlas to Reflect Shrinking Ice

Nat Geo: Twilight of the Arctic Ice