Arctic Glaciers Face 'Terminal' Decline As Microbes Accelerate Ice Melt

Scientists in Svalbard warn Arctic glaciers are in 'terminal' decline, with microbe-driven biological darkening accelerating ice melt and potentially triggering major climate feedback loops. The Guardian reports: Recent research implicates snow and ice-dwelling microbes in positive feedback loops that can accelerate melting. With more than 70% of the planet's freshwater stored in ice and snow -- and billions of lives sustained by glacier-fed rivers -- this has profound implications everywhere. Yet not all polar microbes amplify global heating. Emerging evidence suggests that certain populations are -- for now -- applying a brake to methane emissions. Microbes that live in surface ice and snow produce dark-colored pigments to harness sunlight and shield themselves from damaging UV light. They also trap dark-colored dust and debris. Together, these factors darken snow and ice, causing it to absorb more heat and melt faster -- a process known as 'biological darkening.'

Microbes also respond to global changes, such as increased nutrients from air pollution, wildfire smoke or wind-blown dust from receding glaciers and expanding drylands. 'The snowpack chemistry is now different to preindustrial era snow,' Edwards says. Rising temperatures and longer melt seasons caused by global heating further accelerate the growth of ice-darkening microbes. Together, these factors have the potential to trigger an amplifying positive feedback loop: ice-darkening microbes nudge up temperatures and accelerate melt, exposing more nutrient-rich debris that encourage the growth of yet more microbes, which darken the surface further still.

Each summer, a biologically darkened zone, visible from space, covering at least 100,000 sq km, appears on the south-western part of the Greenland ice sheet. According to a 2020 study, microbes there are responsible for 4.4 to 6.0-gigatons of runoff, representing up to 13% of total melt, from an ice mass that holds enough water to raise global sea levels by more than 7 meters. These effects are acknowledged in IPCC reports but not yet incorporated into climate projection models. Across the European Alps, Himalayas, central Asia and beyond, at least 2 billion people depend on glacial meltwater for drinking water, agriculture and hydropower. Yet even if the world meets Paris targets, half these glaciers will not survive this century.

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