Greenland’s ice sheets tell a climate-change story of their own
A Norwegian-led team of scientists reports on an 11-year study of ice sheet growth in Greenland’s vast interior. The findings, planned for publication in a leading scientific journal, reveal a strong relationship between Greenland’s ice sheets and global warming.
Greenland, or more particularly its huge ice sheets, has been the focus of increasing attention of late. Elevation or melting of these sheets can tell scientists much about regional – and ultimately – global climate change.
|Greenland’s interior ice sheet has grown, says a team of climate scientists at the Nansen Centers in Bergen and St. Petersburg.|
An international team of climatologists and oceanographers, led by the Nansen Environmental and Remote Sensing Center (NERSC) in Norway, estimates that Greenland’s interior ice sheet has grown, on average, 6cm per year in areas above 1 500m between 1992 and 2003. This contradicts earlier reports of high-elevation balance. Below 1 500m, on the other hand, the team reports ice sheet thinning by 2cm a year.
The average overall increase is 5.4cm per year, or equivalent to approximately 60cm during the 11 years – but perhaps as low 54cm a year when ‘isostatic uplift’ (post-Ice Age phenomenon causing the land to rise) is taken into account. Ola M. Johannessen of NERSC says the sheet growth is due to increased snowfall brought about by variability in regional atmospheric circulation, or the so-called North Atlantic Oscillation (NAO). As reported in Science, using Greenland’s ice sheet figures and a special index, Johannessen and team confirm, for the first time, a direct relationship between the elevation change and the NAO.
“The strong correlation between winter elevation changes and the NAO index suggests an underappreciated role of the winter season and the NAO for elevation changes – a wildcard in Greenland ice sheet mass-balance scenarios under global warming,” notes the team.
But they caution about drawing hasty conclusions from this sort of finding. Recent evidence of ice sheet growth found by Johannessen and company “does not necessarily reflect a long-term or future trend”, they say. “Natural variability in the high-latitude climate system, including the NAO, is very large,” so even their 11-year-long study is still short in the grand scale of climate change.
This sort of research on “climate forcing” is far from straightforward, the scientists insist . Numerous variables, such as solar radiation and greenhouse gas levels, surface temperature, cloud cover, glacier-flow dynamics, precipitation and so on, can play into it. What’s more, it is difficult to collect reliable ice-sheet readings of the vast high-altitude regions of Greenland.
There is a clear need for continued monitoring and further research using new satellite altimeters and other observations, together with numerical models, to calculate the Greenland ice sheet melt versus gain balance, they conclude. In fact, large sums have been set aside in the European Union’s Sixth Framework Programme (FP6) for research into climate change.
NERSC (research institute affiliated to Bergen University)
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