Response of glaciers to climate change

The response of glaciers to climate change depends on their size and shape, but most of them react to a change in mass balance within a few years by adjusting the position of their snout. The glacier will then continue to retreat or advance for many years or decades before completely adjusting to a change in climate. Short and steep valley glaciers adjust in a decade or two, but larger and less steep glaciers have a much longer response time. The response of glaciers to a change in mass balance thus depends on the slope and shape of the underlying bed, as well as on the existence of glacial lakes, that increase the melting. The ablation and the duration of the ablation season are increased in a warming climate. The increased meltwater, leads to increased sliding as the water lubricates the glacial bed, and calving is intensified for glaciers that enter the sea.

 

Glacial lakes enhance melting such as Jökulsárlón on Breiðamerkursandur. Photo: Hrafnhildur Hannesdóttir, 2006.

Glacial lakes enhance melting such as Jökulsárlón on Breiðamerkursandur. Photo: Hrafnhildur Hannesdóttir, 2006.

 

The sensitivity of glaciers to variations in climate is defined as the change in mass balance or glacier volume in response to a given climate change (temperature and precipitation). Recent modelling studies of the response of Skálafellsjökull, Heinabergsjökull and Fláajökull outlet glaciers to changes in temperature and precipitation show that they would lose 25–35% of their volume as a consequence of a warming of only 1°C. A warming of 2°C would eventually (after approximately 100 years of the model run) lead to loss of almost 60% of the original ice volume. We might think that 1°C warming is not much, but such a change affects the glaciers considerably.

Drastic changes are currently taking place in Greenland and Antarctica, and the rate of change is faster than according to previous predictions. The ablation areas have increased in size, reaching higher elevations, meltwater collects in numerous surface ponds, which suddenly drain as the water flows down moulins to the glacier bed. This development leads to an increase in the velocity of the ice flow and consequently in the rate of calving of outlet glaciers that enter the ocean.

 

A surface lake in Greenland. A growing network of lakes on the Greenland ice sheet has been found to drain in a chain reaction that speeds up the flow of the ice sheet. Photo: Timo Lieber 

A surface lake in Greenland. A growing network of lakes on the Greenland ice sheet has been found to drain in a chain reaction that speeds up the flow of the ice sheet. Photo: Timo Lieber

 

Surface lakes in Greenland. Photo: Joughin/UW Polar Science Center.

Surface lakes in Greenland. Photo: Joughin/UW Polar Science Center.