Friday, June 29, 2012

Greenland Ice Sheet Melt Nearing Critical ‘Tipping Point’

The Greenland ice sheet is poised for another record melt this year, and is approaching a "tipping point" into a new and more dangerous melt regime in which the summer melt area covers the entire land mass, according to new findings from polar researchers.

The ice sheet is the focus of scientific research because its fate has huge implications for global sea levels, which are already rising as ice sheets melt and the ocean warms, exposing coastal locations to greater damage from storm surge-related flooding.

Greenland's ice has been melting faster than many scientists expected just a decade ago, spurred by warming sea and land temperatures, changing weather patterns, and other factors. Until now, though, most of the focus has been on ice sheet dynamics — how quickly Greenland's glaciers are flowing into the sea. But the new research raises a different basis for concern.

The new findings show that the reflectivity of the Greenland ice sheet, particularly the high-elevation areas where snow typically accumulates year-round, have reached a record low since records began in 2000. This indicates that the ice sheet is absorbing more energy than normal, potentially leading to another record melt year — just two years after the 2010 record melt season. More


Wednesday, June 6, 2012

Exceptional Rise in Ancient Sea Levels Revealed

ScienceDaily (June 5, 2012) — Since the end of the last ice age 21,000 years ago, our planet has seen ocean levels rise by 120 meters to reach their current levels. This increase has not been constant, rather punctuated by rapid accelerations, linked to massive outburst floods from the ice caps. The largest increase, known by paleoclimatologists as 'Melt-Water Pulse 1A', proved to be enigmatic in many respects. A study recently published inNature by a team from the CEREGE laboratory in collaboration with the universities of Tokyo and Oxford has revealed the mysteries of this event, without doubt one of the most important in the last deglaciation.

A spectacular rise

The research has primarily confirmed the existence of this exceptional event, which had been controversial in some regards. Its chronology, amplitude and duration have now been defined. It began precisely 14,650 years ago and coincides with the start of the warm period known as the 'Bølling oscillation', which marked the end of the ice age. The rise in sea levels at that time was an average of 14m worldwide, over less than 350 years. This corresponds to a rate of 40mm per year -- compared to the 3mm per year we are currently experiencing.

Coral: a climate archive

To describe this remarkable event, researchers analysed cores taken from the coral reef surrounding Tahiti, Polynesia, during the international IODP 310 'Tahiti Sea Level'(4) expedition. The corals that built these reefs and atolls are excellent indicators of sea level variation* and also provide a virtual archive of previous climates(5).

Using reconstructions of sea levels from the fossilised corals as well as geophysical simulations, scientists have been able to identify the source of this accelerated rise in sea levels. They have demonstrated that the Antarctic ice cap was responsible for up to 50% of these increases. Experts had previously believed that only melting ice from the Northern hemisphere had contributed to Melt-Water Pulse 1A, particularly the Laurentide ice cap that covered a large part of North America. More