A mostly molten iron core, a solid outer mantle, and literally millions of tons of water (332.5 million cubic miles, of which 321 million are the oceans, according to the U.S. Geological Survey) keep body and soul together. What’s missing? The icing on the top of the planet is topped by layers of snow and ice at the North Pole, South Pole, and mountain summits around the world, and the pace of change in these frozen environments is outstripping all past developments.
Consider our snow-capped mountains: Sperry Glacier in Glacier National Park, for example, has shrunk from more than 800 acres (320 ha) in 1901 to less than 250 acres (100 ha) today; the snows of Kilimanjaro have melted more than 80% since 1912; glaciers in the central and eastern Himalaya are melting so fast that researchers believe that most of them could disappear by 2035; Greenland’s ice sheet is shrinking; and on it goes. As the glaciers and snow caps melt, more freshwater flows into the seas, and the ocean water warms up and expands, causing sea levels to rise. Thawing of the permafrost has caused subsidence, vegetative changes, and pent-up methane (a powerful greenhouse gas) explosions from Alaska to Siberia. And subsidence and rising sea levels are affecting island nations and coastal areas from Louisiana (where the coasts are sinking by about three feet a century) to Florida and beyond.
What about the poles? The mass of ice that floats on the Arctic Ocean is now warming up three to four times faster than the rest of the planet, diluting the sea water and reducing ice floes on which animals depend, but, more importantly, reducing the region’s ability to reflect solar energy back into space. If the remaining Arctic Sea ice disappears, research models show that this reduced albedo effect will be tantamount to adding 1 trillion tons of CO2 or the equivalent of 25 years of global CO2 emissions into the atmosphere! Antarctica, on the other hand, is a “frozen” continent that theoretically should not budge, at least not noticeably, given the geological scale of movement. Well, think again because scientists studying the continent’s thick ice sheet have detected alarming changes in its coastal glaciers that are largely attributable to global warming.
The Thwaites Western Ice Shelf in Western Antarctic is a particular cause for alarm. Airborne measurements, based on averaging with a flying speed of 150 km an hour, tell one story; in situ measurements taken by probes through the ice and radar pulled at 3 km/hour tell another story.
Thwaites Glacier flows into an ice shelf with two main “tongues.” The faster-moving Thwaites Western Ice Shelf floating into the Southern Ocean acts as a dam for Thwaites Glacier; the slower-moving Thwaites Eastern Ice Shelf is pinned against a submarine mountain range that likewise acts like a plug. As the glacier passes slowly over the grounding line (where it leaves its land base), trenches perpendicular to the direction of movement form. Then, as the ice floats over the sea, warm seawater melts the underside, producing a buoyant cushion of cold melt water that insulates the floating ice. However, step-like terracing of the trenches increases melting (5x faster than horizontal surfaces) due to turbulent water currents and the formation of crevasses (with vertical walls melting up to 10 times as fast as the horizontal surfaces) that could eventually cause the ice shelf to splinter into pieces and let the unimpeded glacier flow faster into the sea. Finally, currents can likewise transfer heat from one ice shelf to the next.
The western ice tongue has lost 80% of its area in the past 25 years, while the eastern shelf pinned against the submarine mountain ridge has shrunk only 15%. Still, at the current, although less than previously estimated, melt rate, this eastern shelf is expected to lift off the mountain tops in the next ten years and split into icebergs. GPS data from on-site stations show an increase in the ice shelf’s seaward movement from 620 to 980 meters a year between late 2019 and early 2022.
Thwaites Glacier, which is now losing 75 billion tons (and rising) of ice every year, holds enough ice to raise the global sea level by about 2 feet (65 cm). Its disappearance would destabilize much of the rest of the West Antarctic Ice Sheet, which contains enough ice to raise sea levels by more than ten feet (3.2 m). Optimistic greenhouse gas emissions scenarios project an at least 2-meter sea-level rise by 2050, putting some 10 million U.S. residents below the high-tide line. If Thwaites Glacier collapses, the rise is 5 meters, threatening at least 20 million people in the U.S. and another 50-100 million worldwide.
The IPCC’s AR6 Synthesis Report: Climate Change 2023 has just been released. Maybe check it out (www.ipcc.ch), along with the 2019 special report The Ocean and Cryosphere in a Changing Climate, for solutions? Water, water everywhere – let’s not head for the drink!
More on the matter on the International Thwaites Glacier Collaboration’s website (https://thwaitesglacier.org) and from Nature (https://www.nature.com), Scientific American (November 2022 issue), National Geographic (https://www.nationalgeographic.com), and many other publications.