A clearer picture of the overall mass of the ice cap

Fluctuations in the masses of the world's largest ice caps have important consequences for future sea-level rise, but it has never been easy to measure the magnitude of the interactions between the conditions. atmospheric, snow inputs and melt processes due to the size and remoteness inherent in glacial landscapes. .

According to a new study co-authored by researchers from the University of Colorado at Boulder, NASA, the University of Utrecht and the Delft University of Technology, many progress has been made over the last ten years. Geophysical Review.

The study presents improvements to satellite imagery and remote sensing equipment that allowed scientists to measure ice mass in more detail than ever before.

"We have come a long way in the last ten years in terms of observation," said Jan Lenaerts, senior research author and assistant professor in the Department of Atmospheric Sciences and Oceans (ATOC). ) from CU Boulder. "Knowing what happens to ice sheets in terms of incoming mass, outgoing mass allows us to better relate climate variations to the ice mass and how much the mass has changed over time."

The ice sheets predominantly gain in mass due to rainfall and are lost due to the release of solid ice and meltwater runoff. Precipitation and runoff, as well as other surface processes, collectively determine the surface mass balance. The Antarctic Ice Sheet, the largest in the world, is cold all year round and melts very little in the summer. A slight increase or decrease in annual snowfall can therefore have a considerable impact on the surface mass, because the addition or subtraction is composed over a very large area.

"Snowfall dominates Antarctica and will remain so for the next decades," Lenaerts said. "And we have seen that when global warming warms the atmosphere, more snow falls, which somewhat lessens the loss of mass of the icecap. Greenland, on the other hand, is experiencing a melting summer abundant, controlling much of its future ice loss. "

In the past, climate models would have been unable to render the subtleties of snowfall in such a remote region. Now, thanks to automated weather stations, airborne sensors and satellites in Earth orbit, such as NASA's Gravity Recovery and Climate Experiment (GRACE) mission, these models have been significantly improved. They produce a realistic surface ice sheet mass balance, allow for greater spatial accuracy and take into account regional variations as well as the redistribution of wind-driven snow – a degree of detail that would never have been heard at the beginning of the 2000's.

"If you do not have the right variable, you're starting on the wrong foot," Lenaerts said. "We focused on the snowfall because they have a great influence on the destiny of the ice cap, and the airborne observations and the satellites made it possible to better visualize all these processes."

Ground radar systems and ice core samples provide useful historical records, allowing scientists to go back in time and observe changes in the ice sheet over long periods of time. But while current technologies allow more extensive spatial monitoring, they do not measure the density of snow, a crucial variable to translate these measurements into mass changes.

The greatest opportunity may lie in cosmic ray meters, which directly measure surface mass balance by measuring neutrons produced by cosmic ray collisions in the Earth 's atmosphere, which persist in the atmosphere. water and can be read by a sensor. Over long periods, a set of these devices could theoretically provide even more detailed details.

Altogether, said Lenaerts, the field of ice sheet observation has matured in recent years, but it should still benefit from additional resources.

"The research community that studies these issues is still relatively small, but it's already a global community and the interest is growing," he said. "We would like to come to a point where ice cap mass processes are taken into account in global climate and earth system models, in order to really show that bigger picture."