Effect of melting water on glaciers only a ‘minor’ worry

The lubricating effect of melting water on glaciers will have only a “minor” role in future sea-level rise, according to new research.

Scientists had feared that melt-water which trickles down through ice could dramatically speed up the movement of glaciers as it acts as a lubricant between the ice and the ground it moves over.

But a University of Bristol team found it is likely to have a minor role in sea-level rise compared with effects such as iceberg production and surface melt.

Results from computer modelling — based on fieldwork observations in Greenland — revealed that by the year 2200 lubrication would add only a maximum of 8mm to sea-level rise. This is less than 5% of the total projected contribution from the Greenland ice sheet.

Some simulations found the lubricating effect could even have a negative impact on sea-level rise — leading to a lowering of sea-level when the other major factors were ignored.

Sarah Shannon is lead author of the research, which is published in Proceedings of The National Academy of Sciences of The United States of America. “This is an important step forward in our understanding of the factors that control sea-level rise from the Greenland ice sheet,” she said.

“Our results show that melt-water-enhanced lubrication will have a minor contribution to future sea-level rise. Future mass loss will be governed by changes in surface melt-water run-off or iceberg calving.”

Previous studies of the effects of melt-water on the speed of ice movement assumed water created cavities at the bottom of ice masses. These cavities lifted the ice slightly and acted as a lubricant, speeding up flow.

The theory led scientists to think that increased melt-water would lead directly to more lubrication and a consequent speeding up of the ice flow.

But the Bristol study took into account observations indicating larger amounts of melt-water may form channels beneath the ice that drain water away. This would reduce the water’s lubricating effect.

The research concluded that the effect on sea level is small, regardless of whether melt-water increases or decreases. Dr Shannon added: “We found that the melt-water would lead to a redistribution of the ice, but not necessarily to an increase in flow.”

The findings are part of research undertaken through the European-funded ice2sea programme.

Earlier research from ice2sea found changes in surface melting of the ice sheet will be the major factor in sea-level rise contributions from Greenland.

Professor David Vaughan, ice2sea co-ordinator, said: “This is important work but it’s no reason for complacency. While this work shows that the process of lubrication of ice flow by surface melting is rather insignificant, our projections are still that Greenland will be a major source of future sea-level rise.

“As we have reported earlier this year, run-off of surface melt water directly into the ocean and increased iceberg calving are likely to dominate.”