Thicker, older Arctic ice is melting quicker than thinner, younger ice, a NASA study reports. The finding means that Arctic ice cover is even more vulnerable to climate change than previously suspected, the authors write.
The thicker ice in question, named multi-year ice, lasts longer than one summer compared with thinner perennial ice that melts each year.
NASA researchers found that multi-year sea ice that covers the Arctic Ocean has fallen by 15 percent per decade since 1980, a greater loss than the observed 12 percent-per-decade decline in the more transient perennial ice.
The reduction in multi-year ice means the average thickness of the Arctic ice cover is diminishing. Coupled with other factors, the melting multi-year ice poses a dangerous trend that is very hard to reverse, according to the study authors.
At the same time, the surface temperature in the Arctic is going up, which results in a shorter ice-forming season, Joey Comiso, lead author and a senior scientist at NASA's Goddard Space Flight Center, said in a statement.
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It would take a persistent cold spell for most multi-year sea ice and other ice types to grow thick enough in the winter to survive the summer melt season and reverse the trend, he said.
Surface temperature across the Arctic has risen 4.2 degrees Fahrenheit (2.4 degrees Celsius) over the last 100 years, according to the EPA. The temperature increase in the Arctic is three times greater than that observed over the rest of the planet, researchers said.
Multi-year ice levels reached their second-lowest on record in 2012; the lowest was in 2008, when ice levels averaged about 55 percent down from the 1970s. The ice levels rebounded in subsequent years but dipped again in 2012.
The Journal of Climate published the study Wednesday.
Melting sea ice plays a large role in climate change and the reduction can be disastrous for species that call the Arctic home, according to Environmental Protection Agency officials.
Melting ice contributed to sea levels that rose 5 to 6 inches over the last century, according to the EPA. A higher sea level means coastal ecosystems such as salt marshes and mangroves are at risk of being destroyed and cities along coastal areas are at an increased risk of flooding, according to the EPA.
A reduction in sea ice also means that the habitat of animals such as seals and polar bears will shrink, EPA officials said.
Global warming must be stopped in order to mitigate the loss of the Arctic ice cover, according to the National Resources Defense Council, an environmental activist group. By reducing the world's dependence on fossil fuels and using cleaner energy technologies, the reduction in sea ice can be lessened, the NRDC says on its website.