When glaciers recede, they leave barren landscapes behind. Dust from these surfaces can influence clouds high above, both how they form and how long they last, according to a recent study published in Nature Geoscience journal. Researchers on the Norwegian archipelago of Svalbard found wind-blown dust from receding glaciers is a catalyst for the formation of ice particle in clouds, impacting Arctic cloud development, lifetime, and reflectivity.
Glacier-sourced dust is made up of fine minerals and organic matter, pulverized over the millennia by the immense weight and slow scouring of glacier ice. The source of the organic matter is undetermined, yet the research team believes those particles are the key to the ice-nucleating ability of glacier dust.
In the low and middle latitudes, dust in the atmosphere is known to scatter light and cause air to condense and form clouds. Whether high-latitude dust emissions have a similar impact on Arctic clouds is not as well understood.
Yutaka Tobo, an assistant professor at Japan’s National Institute of Polar Research, led a research team to see how the dust was affecting clouds. In particular, Tobo wondered whether they were triggering the formation of ice crystals, which can cause clouds to condense at low temperatures. Ice nucleating particles, Tobo’s team found, shorten cloud lifetime by prompting precipitation. Since icy clouds are less reflective than liquid-based clouds, the cloud’s capacity to reflect incoming light is also diminished, a key factor in the Earth’s ability to regulate its temperature.
“Few studies have focused on the possible contribution of dusts released from high-latitude sources to ice nucleation in Arctic mixed-phase clouds,” Tobo told GlacierHub. “If there are more ice nucleating particles around, the cloud properties and lifetime are expected to be dramatically altered.”
Though the field work in Svalbard was mainly performed within the framework of a Japanese Arctic research project, Tobo enlisted scientists from Colorado State University, whom he worked with previously, while a team from Cornell University performed global aerosol model simulations, including high-latitude dusts.
Natalie Mahowald, a professor in the department of earth and atmospheric science at Cornell University, was one of the modellers involved in the study. “It is very exciting that these dust particles are much better ice nuclei, which will help us understand more about the climate system and how ice clouds will respond,” she told GlacierHub. “This could be especially important to understand what happened during the last interglacial, when these glaciated sources were much bigger.”
What makes the glacier dust particularly effective at nucleating ice is the small amount of organic matter within it. Interestingly, the Svalbard glacial plain the researchers studied, is devoid of vegetation or any apparent source of organic material.
Tom Hill, a co-author of the study, is a researcher at Colorado State who specializes in molecular microbial ecology. “The source of the outwash organic matter intrigues me,” Hill said. “There isn’t much of it by percentage but it’s enriched in ice nuclei. We still know very little about ice nucleating microbes in soils, so it could be something entirely new.”
The team suspects the organic particles were washed down from microbial sources from higher up on the glacier. “Further studies will be necessary to understand the major sources of organic matter contained in the outwash,” Tobo told GlacierHub.
Through its influence on clouds, glacier dust––and the organic ice-nucleating matter within it––have implications for the Earth’s climate.
How clouds, which are responsible for more than half of the Earth’s reflective capacity, respond to climate change remains one of the greatest uncertainties in climate science. The wide range of cloud type, altitude, and composition make their effect on Earth’s climate difficult to measure quantitatively. Clouds have opposing effects: cooling, by reflecting solar radiation back into space; and warming, by trapping radiation from the Earth’s surface.
At a fundamental level, climate models are built on an accurate accounting of incoming and reflected solar radiation. Any uncertainty in the atmospheric radiation budget sends errors rippling through climate projections.
In the Arctic, a region especially sensitive to the effects of climate change, comprehensive understanding of what causes clouds to form there – and dissipate – is central to projecting climate impacts.
Though the study focused on the effect of glacier dust on cloud properties and lifetime, the results suggest larger questions about the impact of glacier dust on cloud reflectivity.
A decline in the reflective capability of clouds could degrade the Earth’s ability to moderate its temperature. Paul DeMott, one of the study’s co-authors, told GlacierHub that he was careful not make conclusions about the role of glacier dust in cloud reflectivity, though he acknowledged that it is “a natural, if simplistic, way of thinking about it.”
Whether or not a cloud contains ice particles is a primary determinant of its reflective capacity, as well as heat-trapping ability. Ice crystals allow more light to pass through clouds, while effectively absorbing outgoing infrared radiation.
Glaciated clouds – those containing ice particles rather than liquid droplets – are unable to reflect as much light as clouds with liquid water. The dust from receding glaciers, the researchers found, is especially adept at glaciating clouds. In other words, clouds formed by glacier dust allow greater amounts of heat to enter Earth’s atmosphere.
A study published in Proceedings of the National Academy of Sciences in March 2018 found low levels of ice-nucleating particles in the Southern Ocean resulted in higher cloud reflectivity – meaning more ice-nucleating particles would do the opposite. More ice-nucleating particles would decrease cloud reflectivity.
As warming from the human-driven climate crisis accelerates, glacier dust is expected to become more abundant, with consequences for Arctic cloud cover and the Earth’s temperature, which depends on the reflectivity and heat-trapping ability of clouds. The study’s conclusion, that ice nucleating particles in glacier dust affect cloud properties, underscores the interconnectedness of natural systems, and their sensitivities.
NASA researcher Patrick Taylor, who was uninvolved with the Nature study told Scientific American, “We really do need to focus on these Arctic clouds because we don’t know a lot about them.” Taylor continued, “and everything we do know about them is pointing to them having this central role in how the Arctic climate system is going to evolve going forward.”
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