Morass of icebergs that have calved off Jakobshaven, the largest glacier in Greenland. Credit: Professor Jonathan Bamber, University of Bristol

Land ice, particularly from Greenland and Antarctica, is contributing more and more to sea level rise in recent years, according to a new study.

Researchers from the University of Bristol have discovered a six-fold increase in the annual land ice contribution to global sea level rise from the mid-1990s to the early 2010s, particularly in recent years.

Land ice is permanent ice on Earth’s surface, which includes the two ice sheets that cover Antarctica and Greenland, as well as numerous smaller glaciers and ice caps. Over the course of the 20th century, melting glaciers and ice caps dominated the overall contribution of land ice to global sea level rise.

Researchers currently believe that ice sheets are the largest potential source of future sea level rise and represent the largest uncertainty in projections for future sea level.

However, over the last few decades, the contribution from the Greenland and Antarctic ice sheets has accelerated.

The team found that between 2012 and 2016, land ice contributed around 1.85 millimeters per year to global sea level rise, with Greenland representing 37 percent of the total, glaciers and ice caps representing 35 percent, and Antarctica representing the remaining 28 percent.

Since 1992, scientists have used satellite observations to measure the land ice contribution to sea level rise. However, different satellite sensors provide unique, but occasionally conflicting results, leading to confusing and often inconsistent estimates of land ice trends.

The Intergovernmental Panel on Climate Change's (IPCC) Fifth Assessment Report (AR5) in 2014 attempted to synthesize estimates published up to early 2013. Scientists since then have advanced in understanding the origin of the inconsistences, reducing uncertainties in estimates and extending time series.

“Our analysis draws on many earlier studies along with new, previously unpublished data and shows that in just over two decades land ice has gone from making a modest contribution to being by far the dominant source of sea level rise,” lead author Jonathan Bamber, a professor at the University of Bristol’s School of Geographical Sciences, said in a statement. “It is intended as comprehensive review of our understanding of current land ice trends and their contribution to contemporary sea level rise.

“It is also, as far as we are aware, the first study since IPCC AR5 that has attempted to combine post-AR5 estimates in a rigorous and holistic way,” he added. “In this sense it should be of considerable interest to the community, providing an updated and extended synthesized estimate of a key component (land-ice) of the sea-level budget.”

The authors were funded as part of a five-year European Research Council project, GlobalMass, which aims to-- for the first time at a global scale-rigorously combine satellite and in-situ data related to different aspects of the sea level budget, so that observed sea level rise can be attributed to its component parts.