On Sept. 27, the Intergovernmental Panel on Climate Change issued its latest release, which made bold statements about human activity's impact on the climate. Among the areas studied to observe climate changes were vegetation, surface, ocean and atmospheric temperatures and the state of the cryosphere, or planetary ice.
Ice on Earth is measured and monitored in several ways, most notably through ice sheets and polar ice caps. Because of the many sources for surface ice across the globe, reports and debates on the growth or loss of ice can often be misleading. What may be true for ice in one particular location is not always indicative of the state of global ice as a whole, nor is an individual example of loss or growth able to provide any substantial information on the topic of climate change, for either side of the debate.
The Greenland ice sheet, for example, has been rapidly losing mass over recent years. Scientists are recording increased sea level rise at a compatible rate to the ice loss. In 2012, NASA noted the highest loss of ice in the area for over 30 years. While some melting is normal for the area during the summer months, losses in unusual places contributed to the increased displacement of ice.
Higher elevations will typically experience some melting that quickly refreezes versus ice melt at the coasts which flow right into the ocean. While an average summer will bring a 50-percent loss of ice in the region, satellite images from last season show an estimated 97-percent loss.
Extent of surface melt over Greenland's ice sheet on July 8, 2012, (left) and July 12, 2012 (right). Measurements from three satellites showed that on July 8, about 40 percent of the ice sheet had undergone thawing at or near the surface. In just a few days, the melting had dramatically accelerated and an estimated 97 percent of the ice sheet surface had thawed by July 12. Jesse Allen, NASA Earth Observatory, and Nicolo E. DiGirolamo, SSAI and Cryospheric Sciences Laboratory.
While there has been less ice melt this season, the overall amount of that lost is still much greater than it was years ago. Arctic sea ice in the area has also been on the decline.
Using reports from NASA, NOAA and the National Snow and Ice Data Center, Earth Gauge states that "Arctic sea ice has experienced an overall trend of 12-percent decline per decade since the late 1970s. During the last 60 years, the Arctic has warmed by more than 3.5 degrees F (2 degrees C) and the remaining ice cover is 50 percent thinner than in previous decades."
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Sea ice is shrinking at the northern pole, but at the southern pole it is actually increasing, a point often used in the climate debate by those on the opposing side.
John Cook, the climate communication fellow for the Global Change Institute at the University of Queensland, explains that in Antarctica, satellite data shows an increase in sea ice. However, studies have shown that the South Ocean is actually warming, more rapidly than all other oceans on Earth. Decreased ozone layers over Antarctica, which cause stratospheric cooling that leads to ice-pushing winds, as well as changes in ocean circulation, which can move warmer, saltier water closer to the surface and increase melting, could count for the changes in ice levels more than temperatures alone.
The University of Washington's Hannah Hickey explained that the thickness of the ice is also a factor. Remarkably strong Antarctic winds push ice together to create a thick, rigid quality to the ice. Despite rising water temperatures, this ice is able to reform together in this way and, because of its structure, will also last longer.
This chart from a report by Jinlun Zhang of the Polar Science Center, Applied Physics Laboratory, College of Ocean and Fishery Sciences, University of Washington, Seattle, Wash., shows that although Antarctic sea ice has been expanding, it does not necessarily signify a cooling of the South Ocean's waters.
Meanwhile, though the Antarctic sea ice is increasing, land ice is consistently decreasing. This has led to confusion in the climate change or sea ice loss debates, as some will cite an increase in Antarctic ice to support their claims and others will cite its losses. Technically, both sides are right, but neither is acknowledging the state of the area's ice as a whole.
Dr. Chris Forest, an associate professor of climate dynamics with Penn State University, emphasized to AccuWeather.com that climate trends are about the long term.
"Sea ice has certainly been in decline since the observations by satellites, and if you look at the records of sea ice over the past 10 years, sea ice grew with respect to the previous year but is still much lower than it was 20 years ago. So the sea ice area is a great example of how you have to look at long-term trends. You can't look at just year-to-year variability; you have to look at long-term changes in the climate, long-term changes in the sea ice as a result."
When discussing ice melt and its relation to a changing climate, individual or single-year examples of a loss or growth may not be enough to adequately act as evidence, for either side of the issue. No conclusions can be made based on a single year or single event, it needs to be taken as a whole and looked at as a long-term pattern.
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