Armed with 42,000 observations from around 2,300 glaciers, an international team of scientists at the World Glacier Monitoring Service (WGMS) have been analysing how glacier melt rates have changed since records began in 1600 AD.
‘The observed glaciers currently lose between half and one metre of its ice thickness every year,’ explains Michael Zemp, Director of the WGMS and lead author of the study. ‘This is two to three times more than the corresponding average for the 20th century.’
Generally, glaciologists are selective of data in order to focus on a particular region or feature. This study, however, collated observational data of glacier fronts via national correspondents in more than 30 countries. This was in order to compare observations from the first decade of the 21st century to all earlier data.
The data gives clear evidence that the current rate of glacier melt has not occurred before, at least since records began. The fronts of the glaciers have been retreating at a rate ‘without precedent’ for the first decade of the 21st century. While there have been periods of readvancement, these have been relatively short events and have been restricted to particular regions of glaciers. These events have not come close to reaching the the maximum positions of the Little Ice Age, a period of colder seasons and glacier growth recorded experienced in the 1300s through to the 1800s.
What’s more, the world’s glaciers are expected to continue their rate of melt, even if the climate remains stable. This is because glacier lengths have a relatively delayed reaction to climate change. Over periods of years, changes in air temperatures affect the energy balance on the surface of the glacier, cumulatively altering the volume and thickness of the ice which eventually causes internal deformation and basal sliding. It is these dynamic reactions that finally lead to glacier length changes that we can see on the glacier fronts.
As it stands, most glaciers are now in a state of strong imbalance with current climate conditions, and are destined for further ice loss, regardless of climate predictions. If the climate continues to warm as is forecasted, the team anticipates further glacier loss beyond that seen throughout history.
People have been observing the seasonal melt of glaciers for centuries, and in a variety of ways. Before satellite data was available, glaciologists measured in situ and took photographs. This study utilised all of these old records from in situ, airborne, and satellite-borne observations, supported by reconstructions of pictures and written sources. ‘Exact measurements of this ice loss are reported from a few hundred glaciers only,’ said Zemp, ‘however, these results are qualitatively confirmed from field and satellite-based observations for tens of thousands of glaciers around the world.’