Could Greenland and Antarctica be losing and gaining ice at the same time? As it turns out, the answer is Yes. A recent study published in Science has confirmed that the coastal ice loss is much greater than the mainland ice gain. In short, “the meltdown is winning in both Greenland and Antarctica.“
NASA ICESat (2003-2008) and ICESat-2 (2018-present) satellite missions were designed to measure the thickness of the ice sheets in Greenland and Antarctica, with a goal of discovering how the sheets have changed over time. ICESat-2 is hoped to capture the changes since the launch of the original ICESat mission.
How Do ICESat Missions Work?
The satellites measure the height of ice near the Earth’s poles by bouncing laser beams off the ice surface. Satellite position and distance in space is known, and one could say fixed, the missions measure how much time it takes for the reflected laser light to return to the satellite. That is how researchers reveal the changes in the ice height, and subsequently track the changes in thickness.
The results were much anticipated in the scientific community since they allow climatologists to compare the climate models against such detailed real-world data, and potentially fix them if needed. Hopefully, that will ensure more accurate forecasting in the future.
What does the new ICESat-2 data reveal?
Ice Thickening. The missions reveal that ice in eastern Antarctica and central Greenland has indeed thickened between 2003 and 2019, although only slightly. The researchers say that the thickening has occurred due to increased snowfall – another trademark feature of global warming. As the atmosphere warms, more water evaporates from the ocean, and the air is capable of holding in more moisture, leading to higher precipitation rates. So ironically, ice thickening on the mainland due to snowfall is yet another confirmation of the predicted global warming mechanisms. The biggest gains were seen at the Queen Maud Land in eastern Antarctica, as well as in the northeast and south of central Greenland.
Ice Losses. Unfortunately, the gain in mainland ice is no match for the ice loss on the coasts. Per year, Antarctica and Greenland lost 118 billion and 200 billion tons of land ice, respectively, over the 16-year period (2003-2019).
On Greenland, the greatest coastal loss is happening due to warm summers and frequent heatwaves and in the Arctic region. Greenland’s numerous fjords make the island’s outlet glaciers the most vulnerable to thinning since the now-warm ocean water that surrounds a fjord can quickly and efficiently waste away the ice.
The glaciers Kangerdlugssuaq and Jakobshavn in the south of the island suffered the worst losses – 4 to 6 meters per year.
In Antarctica, the greatest thinning occurred in the regions of western Amundsen and Bellingshausen.
The continent’s ice shelves – floating ice sheets that surround it – were the first become affected by the warming ocean water. Like the ice sheets of the Arctic sea, their loss doesn’t contribute to sea-level rise directly. Still, the shelves act like gatekeepers, resisting the natural tendency of Antarctica’s inland ice to move towards the coasts. When the ice shelves weaken, they allow more ice to flow into the ocean – at a faster rate than the snowfall can compensate.
The study estimates that the combined grounded-ice loss in the studied period contributed to 14 millimeters of sea-level rise.
Smith, B., et al. (2020). Pervasive ice sheet mass loss reflects competing ocean and atmosphere processes. Science, 368(6496), 1239-1242. doi:10.1126/science.aaz5845 https://science.sciencemag.org/content/368/6496/1239
Climate Change – Trends And Patterns. NASA https://gpm.nasa.gov/science/climate-change
Greenland and Antarctica are gaining ice inland, but still losing it overall. Science News. 30 April 2020 https://www.sciencenews.org/article/greenland-antarctica-are-gaining-ice-inland-losing-melting-overall
The North Pole just had an extreme heat wave for the 3rd winter in a row. Vox. 28 February 2018. https://www.vox.com/energy-and-environment/2018/2/27/17053284/arctic-heat-wave-north-pole-climate