These 'tiny' hollow glass spheres used to halt Arctic ice loss are not working — here's why
A proposal to cover Arctic sea ice with layers of tiny hollow glass spheres about the thickness of one human hair has been challenged by a recent study published in the journal Earth's Future.
The new study rejects a claim made in 2018 that hollow glass microspheres, or HGMs, sprayed repeatedly over young Arctic sea ice improve reflectivity or protect the ice from the sun. It demonstrates that using microspheres could actually harm both human society and the planet's climate, emphasizing how important it is to keep an eye on climate mitigation efforts.
When tapping into Earth's dynamic processes for climate control goes wrong
Sea ice aids in regulating ocean and air temperatures. It affects ocean circulation by reflecting most of the Sun's energy back to space. Because of this, the Earth's climate is critically dependent on sea ice area and thickness.
Now, researchers from the University of Alaska Fairbanks Geophysical Institute, led by Melinda Webster, have shown that a solution to make thick ice and decrease climatic temperature could actually speed up sea-ice loss and warm the climate. They reveal this is because placing layers of white hollow glass microspheres onto Arctic sea ice darkens its surface and, therefore, has the opposite effect.
The 2018 study found that using five layers of HGMs reflected 43% of the incoming sunlight while allowing 47% of it to pass through to the surface below. The HGMs take up the remaining 10%. According to Webster's research, the microspheres' 10% absorption of sunlight is sufficient to speed up ice melting and further warm the Arctic environment.
"Our results show that the proposed effort to halt Arctic sea-ice loss has the opposite effect of what is intended," says Webster in a press release. "And that is detrimental to Earth's climate and human society as a whole."
Hollow glass spheres won't save Arctic sea ice in fall, winter, spring, or summer
To reach their conclusion, Webster and Stephen G. Warren of the University of Washington calculated variations in solar radiation across eight typical surface conditions found on Arctic sea ice — each of which has a distinct reflectivity.
Along with these factors, they took cloud cover, the response of the microspheres to sunlight, the intensity of solar radiation at the surface and the top of the atmosphere, seasonal sunshine, and more into account.
Significantly, they based their study on the type of microspheres used in the 2018 study and the exact number of layers.
The research team discovered that while a microsphere coating can be employed to increase the reflectivity of ice in the fall and winter, the effect would be limited. This is because thin ice mainly occurs in these seasons with little sunlight. The thin ice soon gets covered by drifting snow, which increases its surface reflectivity.
HGMs increase the ice's solar absorption — ultimately causing it to melt more quickly than intended
In spring, reflective snow covers ice due to increased solar energy. Microspheres would darken the snow surface due to the snow's high reflectivity. In this case, they increase the ice's solar absorption, ultimately causing it to melt more quickly than intended.
In late spring and early summer, melt ponds (pools of open water that form on sea ice) begin to develop across the sea ice as solar energy increases further. Ponds would seem to be an ideal target for hollow glass microspheres because they are dark and have low reflectivity. However, the team found that this was not the case.
Instead, in an experiment on a Minnesota pond, the buoyant spheres were carried by the wind to the water's edge, where they clumped together as pollen does on ponds and puddles.
'The best bet is for society to reduce the behaviors that continue to contribute to climate change'
When sunlight is at its highest, the months of March, April, May, and June would appear to be the best for applying microspheres but are really the worst for using HGMs.
“The use of microspheres as a way to restore Arctic sea ice isn’t feasible,” states Webster. “While science should continue to explore ways to mitigate global warming, the best bet is for society to reduce the behaviors that continue to contribute to climate change.”
Arctic sea ice might be preserved if its albedo could be increased. To this end, it has been proposed to spread hollow glass microspheres (HGMs) over the ice. We assess the radiative forcing that would result, by considering the areal coverages and spectral albedos of eight representative surface types, as well as the incident solar radiation, cloud properties, and spectral radiative properties of HGMs. HGMs can raise the albedo of new ice, but new ice occurs in autumn and winter when there is little sunlight. In spring the ice is covered by high-albedo, thick snow. In summer the sunlight is intense, and the snow melts, so a substantial area is covered by dark ponds of meltwater, which could be an attractive target for attempted brightening. However, prior studies show that wind blows HGMs to the pond edges. A thin layer of HGMs has about 10% absorptance for solar radiation, so HGMs would darken any surfaces with albedo >0.61, such as snow-covered ice. The net result is the opposite of what was intended: spreading HGMs would warm the Arctic climate and speed sea-ice loss. If non-absorbing HGMs could be manufactured, and if they could be transported and distributed without contamination by dark substances, they could cool the climate. The maximum benefit would be achieved by distribution during the month of May, resulting in an annual average radiative forcing for the Arctic Ocean of −3 Wm−2 if 360 megatons of HGMs were spread onto the ice annually.
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