December 30, 1990 to December 6, 2007 In November 2007, New Zealand's National Institute of Water and Atmospheric Research (NIWA) announced that the amount of ice in the country's southern Alps had decreased by nearly 11% over the past 30 years.

December 30, 1990 to December 6, 2007

In November 2007, New Zealand's National Institute of Water and Atmospheric Research (NIWA) announced that the amount of ice in the country's southern Alps had decreased by nearly 11% over the past 30 years. . NIWA scientists attribute glacier retreat primarily to global warming, saying the 12 largest glaciers will not be able to return to their previous size without significant climate cooling.

Three of the twelve large glaciers appear in this pair of images. The Tasman Glacier, located in the South Island of New Zealand, is the longest glacier in New Zealand. The topmost image was acquired on December 30, 1990 by the Thematic Mapper aboard NASA's Landsat-4 spacecraft and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) at NASA's Landsat-4 spacecraft. The agency's Terra satellite acquired the bottom image on December 6, 2007. Both photos were taken in late spring or early summer in New Zealand. In these false-color images, light blue represents ice and snow, electric blue represents water, green represents vegetation, and brown represents rock or bare ground.

Although it is made of ice, the mouth of the glacier looks a dirty grey-brown color in this image. The color is caused by literal dirt. As glaciers move, they pick up rocks and debris and carry them downstream. From their drab appearance, the Hooker and (especially) Tasman glaciers are more pristine; a pale blue streak on the Hooker glacier testifies to its icy interior. The dark coating on these glaciers absorbs more of the sun's energy and can cause faster melting, but if the insulating layer of dirt and debris is thick enough, it can actually insulate the ice, slowing the melting process.

In the 1990 photo, there is a small lake in the snout of each glacier. According to NIWA scientists, these glacier mouth lakes increase the likelihood of large chunks of ice breaking off the glacier. Additionally, the water hinders the glacier's future growth. In the 2007 photo, both glacial nose lakes are growing, especially the Tasman Glacier. NIWA scientists say the glacier has retreated 5 kilometers (about 3 miles) over the past three decades. They also said New Zealand's glaciers overall lost 5.8 cubic kilometers (about 1.4 cubic miles) during the same period.