Glaciers that flow into the ocean are extremely sensitive to climate

Rising seas are among the greatest threats posed by climate change. Over the next century, ice sheets and glaciers will contribute significantly to sea level rise through melting and "calving" (breaking off) of ice into the ocean.

Observed rates of iceberg calving are not easy to reproduce in computer simulations, and due to their rapid and non-linear fluctuations, are especially calving fluxes difficult to predict under a changing climate. Robust simulation of iceberg calving, and therefore more precise projections of sea level rise, remains one the grand challenges in preparing for a warming world.

"In this study, we compared extensive observations of iceberg calving from Svalbard, Alaska, Greenland, and Antarctica to theoretical developments and advanced computer simulations", explained Dr. Jan Åström of the CSC – IT Centre for Science in Finland.

"We found that the frequency of observed calving events, ranging from 1 to 1 trillion m3, follow universal scaling laws. This means that the probability of calving events obey a particular pattern no matter if they are small or large events – much like the Gutenberg-Richter law for earthquakes. The observations also agree with our computer simulations, where we model calving events as the fracture of millions of individual ice blocks. Cracks will suddenly propagate through the ice blocks, triggering calving events whose size and inter-event time distributions share a striking resemblance to those predicted by a classic theory of self-organised criticality, originally developed as a model of a growing sandpile [the Abelian sandpile model]."

Their results suggest that calving glaciers and ice sheets behave as self-organised critical systems that fluctuate around a critical point, readily flipping between states of sub-critical advance and super-critical retreat in response to changes in climate and geometric conditions.

This means that calving is extremely and unavoidably sensitive to its environment: a slight climate change can mean the difference between very little calving and the complete disintegration of entire ice shelves.

This new view of iceberg calving explains the observed, sudden collapse of ice shelves and sudden retreat of tidewater glaciers as the polar regions slowly warm.

The authors suggest that their results and theoretical framework will guide improvements in our ability to estimate future sea levels.

The study is a Finnish-Swedish-US-Chinese collaboration and has just been published in the journal Nature Geoscience.

More information:

Researcher Martina Schäfer, tel. +358 50 383 9518, smartina.ac(at)gmx.de

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2290.html