|Temperatures rising. (Arctic Climate Impact Assessment)|
Current warming trends in the Arctic will shove the Arctic system into a seasonally ice-free state not seen for more than one million years, according to a new report.
While this is not the first forecast of the melting of Arctic sea ice due to global warming, the authors indicate that not only is melting accelerating, but that they were unable to identify any natural processes that might slow the de-icing of the Arctic, land and sea.
The report—Arctic System on Trajectory to New, Seasonally Ice-Free State—is the result of week-long meeting of an interdisciplinary team of 21 scientists organized by the National Science Foundation’s Arctic System Science (ARCSS) Committee that examined how the Arctic environment and climate interact and how that system would respond as global temperatures rise.
The report by Jonathan T. Overpeck, chair of ARCSS and who also chaired the meeting, and 20 colleagues from the US and Canada appears in the 23 August 2005 Eos, the weekly newspaper of the American Geophysical Union.
What really makes the Arctic different from the rest of the non-polar world is the permanent ice in the ground, in the ocean, and on land. We see all of that ice melting already, and we envision that it will melt back much more dramatically in the future, as we move towards this more permanent ice-free state.
I think probably the biggest surprise of the meeting was that no one could envision any interaction between the components that would act naturally to stop the trajectory to the new system.—Jonathan Overpeck
Such substantial additional melting of Arctic glaciers and on-land ice sheets will raise sea level worldwide, flooding the coastal areas where many of the world’s people live. Melting sea ice has already resulted in dramatic impacts for the indigenous people and animals in the Arctic, which includes parts of Alaska, Canada, Russia, Scandinavia, and Greenland.
The past climates in the Arctic include glacial periods, where sea ice coverage expanded and ice sheets extended into Northern America and Europe, and warmer interglacial periods during which the ice retreats, such as the past 10,000 years. By studying natural data loggers such as ice cores and marine sediments, scientists have a good idea what the “natural envelope” for Arctic climate variations has been for the past million years.
At the workshop, the team of scientists synthesized what is currently known about the Arctic and defined key components that make up the current system. They identified how the components interact, including feedback loops that involve multiple parts of the system.
The team concluded that there were two major amplifying feedbacks in the Arctic system, involving the interplay between sea and land ice, ocean circulation in the North Atlantic, and the amounts of precipitation and evaporation in the system.
For example, the white surface of sea ice reflects radiation from the Sun. As sea ice melts, more solar radiation is absorbed by the dark ocean, which heats up and results in yet more sea ice melting.
The scientists identified one feedback loop that could slow the changes, but they did not see any natural mechanism that could stop the dramatic loss of ice.
In addition to sea and land ice melting, the permafrost, the permanently frozen layer of soil that underlies much of the Arctic landmass, will melt and eventually disappear in some areas. Such thawing could release additional greenhouse gases stored in the permafrost for thousands of years, which would amplify human-induced climate change.
This report comes just two weeks following a report by Russian and British researchers that the sub-arctic region of western Siberia—an area stretching for a million square kilometers—is also melting rapidly.
The news of the dramatic transformation of one of the world’s least visited landscapes comes from Sergei Kirpotin, a botanist at Tomsk State University, Russia, and Judith Marquand at the University of Oxford.
Kirpotin describes an “ecological landslide that is probably irreversible and is undoubtedly connected to climatic warming.” He says that the entire western Siberian sub-Arctic permafrost region has begun to melt, and this “has all happened in the last three or four years.”
Western Siberia has warmed faster than almost anywhere else on the planet, with an increase in average temperatures of some 3° C in the last 40 years. The warming is believed to be a combination of man-made climate change, a cyclical change in atmospheric circulation known as the Arctic oscillation, plus feedbacks caused by melting ice, which exposes bare ground and ocean. These absorb more solar heat than white ice and snow. (New Scientist)
Overpeck, J. T., et al., (2005), Arctic System on Trajectory to New, Seasonally Ice-Free State, Eos, Trans. AGU, 86(34), 309, 312-313.