Glass microspheres won't save Arctic sea ice

Sea ice, by reflecting the majority of the sun's energy back to space, helps regulate ocean and air temperatures and influences ocean circulation. Its area and thickness is of critical importance to Earth's climate.

The new finding is the result of work led by researcher Melinda Webster of the University of Alaska Fairbanks Geophysical Institute. The research was published today in the journal Earth's Future.

The research challenges a claim in a 2018 research paper that repeated spreading of hollow glass microspheres, or HGMs, on young Arctic sea ice will increase reflectivity, protect it from the sun and therefore allow it to mature over time into highly reflective multi-year ice.

Webster's work rejects that claim, finding that placing layers of white hollow glass microspheres onto Arctic sea ice would actually darken its surface, accelerate the loss of sea ice and further warm the climate.

According to the 2018 study, the application of five layers of HGMs reflects 43% of the incoming sunlight and allows 47% to pass through the HGM layers to the surface below. The remaining 10% is absorbed by the HGMs.

That 10% of sunlight retained by the microspheres is enough to hasten the melting of ice and further warm the Arctic atmosphere, Webster's research shows.

"Our results show that the proposed effort to halt Arctic sea-ice loss has the opposite effect of what is intended," Webster said. "And that is detrimental to Earth's climate and human society as a whole."

Webster and colleague Stephen G. Warren of the University of Washington came to their conclusion by calculating changes in solar energy across eight common surface conditions found on Arctic sea ice, each of which have different reflectivities. They also considered seasonal sunlight, the intensity of solar radiation at the surface and at the top of the atmosphere, cloud cover and how the microspheres reacted with sunlight.

They based their research on the type of microspheres used in the 2018 study and on the same number of layers.

The 2018 study did not fully account for the varying surface type reflectivities or variations that would occur depending on the time of year of HGM application.

A layer of microspheres can increase the reflectivity of thin new ice, which is naturally dark, but the effect would be minimal because thin ice mostly occurs in autumn and winter when there is little sunlight. Thin ice soon gets covered by falling and drifting snow, which increases its surface reflectivity.

In spring, solar energy increases with the return of the polar day. At that time, most sea ice is covered by deep, reflective snow. Because of snow's high reflectivity, microspheres would darken the snow surface, increasing its solar absorption and subsequently accelerating its melt -- opposite of what proponents intend.

In late spring and early summer, melt ponds begin to form across the sea ice as solar energy increases. Ponds would seem to be an ideal target for the use of hollow glass microspheres because they are dark and have low reflectivity.

Covering ponds with microspheres will not achieve the desired effect, however. An experiment on a Minnesota pond in the 2018 study showed wind blowing the buoyant spheres to the pond edge, where they clumped, much like pollen does each year on ponds and puddles.

The bottom line?

The months that would seem most favorable for the application of microspheres -- March, April, May and June when sunlight is increasing -- are actually the worst months to apply HGMs.

Fully non-absorbing microspheres, meaning they absorb 0% rather than 10% of the incoming solar energy, might still not be the answer for a reason plaguing both types of the tiny spheres: Quantity. About 360 million tons would be needed for an annual one-time application to cool the climate; that is, if non-absorbing microspheres could be manufactured and dispersed without contamination.

"The use of microspheres as a way to restore Arctic sea ice isn't feasible," Webster said. "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."