5 December 2019
By Helge F. Goessling
A new study shows that a radical geoengineering concept could slow sea ice retreat, but not global warming.
According to a much-debated geoengineering approach, both sea ice retreat and global warming could be slowed by millions of wind-powered pumps, drifting in the sea ice, to promote ice formation during the Arctic winter. Researchers have now, for the first time, tested the concept using a complex climate model.
Their verdict, published in AGU’s journal Earth’s Future, is sobering. Though the approach could potentially delay ice-free Arctic summers for a few more decades, the massive campaign wouldn’t produce any meaningful cooling beyond the Arctic.
Though the idea sounds like science fiction, it’s a serious suggestion to combat climate change. Ten million wind-powered pumps, distributed throughout the Arctic, could promote sea ice formation in the winter. These pumps would continually pump seawater onto the surface of the ice, where it would freeze into thicker sheets that reflect sunlight and could survive summertime melting. Otherwise, the darker ocean would readily absorb the sun’s warming rays. The plan aims to not only slow the loss of Arctic sea ice, but also mitigate remote impacts, such as warming in lower latitudes.
The idea, first proposed by US researchers as ‘Arctic ice management’ in Earth’s Future in 2017, was recently put to the test in a coupled climate model by two experts from the Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research in Germany.
From a physical standpoint, the near-total loss of summertime sea ice — which will likely happen by mid-century under a ‘business-as-usual’ emissions scenario — could indeed be pushed back to the end of the century. However, this grace period would not entail any significant cooling in other parts of the globe.
“We wanted to know whether this manipulation of the Arctic sea ice could work in purely physical terms, and what effects it would have on the climate,” said Lorenzo Zampieri, an environmental physicist at AWI and lead author of the study.
Accordingly, Zampieri modified the climate model so that it would simulate the constant pumping of water onto the sea ice’s surface throughout the winter.
“Normally the growth of the ice is limited by the fact that, as it becomes thicker, the ice increasingly insulates the ocean from the winter cold,” said Helge Goessling, head of the AWI research group and senior author of the study. “For this reason, typically you won’t find an overall thickness of more than a few meters. But the pumps do away with this limiting effect, because new layers are added to the ice from above.”
Initial simulations based on pumps churning seawater onto the ice throughout the Arctic show the ice would gain between one and two meters in thickness each year. According to the climate model, carbon dioxide-driven warming wouldn’t put an end to ice growth until the end of the century.
And what about the effects on the Arctic climate? Summertime warming of the Arctic would in fact be lessened by several degrees Celsius, the study suggests. However, pumping the comparatively warm (-1.8 degrees Celsius; 29 degrees Fahrenheit) water would alter the thermal flow in winter, resulting in a substantial Arctic winter warming. This heat would be transported to and stored in the middle latitudes, where it would keep seawater warm year-round.
The researchers then conducted more realistic simulations in which the pumps were deployed only where the ice was less than two meters thick.
“Two-meter-thick ice already has the best chances of surviving the summertime melting, and by limiting the distribution of pumps in this way, the unnecessary and considerable wintertime warming can also be avoided,” said Zampieri.
In this scenario, undesirable additional warming of the middle latitudes could be avoided, but the scheme would still do little to mitigate climate change. Though the warming of the Arctic in summer would be reduced by roughly one degree Celsius, and the loss of the sea ice could be delayed by roughly 60 years, the increased reflection of sunlight wouldn’t be sufficient to slow climate change outside the Arctic.
Despite evidence that the plan won’t thwart warming in the long-term, such studies are crucial to understand what options are truly feasible, according to Goessling and Zampieri.
“Given the unchecked progression of climate change to date, geoengineering can’t be dismissed as mere nonsense by the climate research community,” Goessling said.
Instead, these ideas need to be subjected to scientific scrutiny. Arctic ice management, both authors agreed, is interesting in its own right, but can’t meaningfully mitigate global climate change.