Snow and Ice
Snow and ice reflect the sun’s energy back to space. Without this white cover, more water can evaporate into the atmosphere where it acts as a greenhouse gas, and the ground absorbs more heat. Snow and ice are melting at rates unseen for thousands of years, and this has profound climate consequences. As with air temperature, most of the melting in our 100 years or so of official record keeping occurred after 1980.
In South America, glaciers are melting at an accelerating pace, gravely endangering the water and power supplies of South Americans in Bolivia, Peru, Colombia, Chile and Ecuador. The melt has reached “critical conditions” in these countries, according to the IPCC. Peru has measured a 22% reduction in total glacier area, while Colombia has seen an 82% reduction.
Between 1940 and 2005, the Chacaltaya glacier in Bolivia (below) shrunk from 0.22 square kilometers to less than 0.01 square kilometers, destroying Bolivia’s ski industry. Especially worrying, this glacier provides part of the water for nearby La Paz, particularly during the dry winter season. In these images, the lines indicate the positions of the former ski lift.
Climate Change 2007: Impacts, Adaption, and Vulnerability. Working Group II Contribution to the Fourth Assessment Report of the Intergovernmental. Panel on Climate Change. Figure 1.1, Cambridge University Press.
Sea ice is dwindling too, especially in the Northern Hemisphere. Satellites have seen average Arctic sea ice shrink by 2.7% per decade from 1978 to 2006, with faster melting in summer.
In summer 2007, the Northwest Passage north of Canada became navigable for the first time as the polar cap melted to its lowest level on record—30 years faster than IPCC scientists had predicted. 2008’s melt was second only to 2007.
In the Southern Hemisphere, sea ice near the Antarctic Peninsula has also decreased significantly as the area warmed by 3°C in the past 50 years.
However, sea ice in Antarctica as a whole has increased slightly, by 0.97%, or about 100,000 km2 per decade since the late 1970s. Recent studies indicate this increase may be caused by additional snowfall over the Antarctic sea ice. Scientists think this may be related to global warming, which promotes more evaporation, providing more atmospheric moisture for precipitation over the southern oceans. It may also be linked to more wind and storms induced by the Antarctic ozone hole, and scientists project that as the hole shrinks and greenhouse gases increase, Antarctic sea ice will eventually melt faster than it is made.