Dwindling of Arctic's oldest ice since 1990
This video is an excellent visualization that shows the loss of Artic sea ice over time. In addition to the supplemental information found on the Climate.gov webpage that supports this video, I like to use this video in conjuction with the information on the 2015 Arctic Report Card Visual Highlights and a classroom exercise. There is an exercise in the Earth Exploration Toolbook titled Whither Arctic Sea Ice? that has students using authentic data, and another one from NSDL titled Exploring the Cryosphere Using Data from the National Snow and Ice Data Center (which includes an exercise for middle school students on the page).