Do we have any low-risk global geoengineering options ready to deploy now? The answer, according to leading US climatologist Alan Robock, is no. So it is unsurprising that interest is starting to turn to more limited, localised ideas that look less perilous.
The latest involve building artificial islands and 100-metre-high walls to prevent a rising tide of melting polar ice. These examples of targeted geoengineering – a new twist on the controversial idea – could prevent the metre or so of sea level rise that is expected to displace millions of coastal dwellers by 2100.
¿ìè¶ÌÊÓƵs to the annual European Geosciences Union meeting last week, a gathering of nearly 15,000 earth and space experts, including Robock, in Vienna, Austria.
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Most geoengineering schemes would directly intervene in the climate across the planet to counter warming, either by reflecting some of the sunlight reaching Earth or by sucking carbon dioxide out of the atmosphere. But the conclusion in Vienna was that their risks are too high, and in some cases too uncertain, to consider them safe to deploy now on a meaningful scale.
According to studies presented at the meeting, solar geoengineering and , for example, but it would also from torrential rain in Europe and North America.
On the other hand, targeting sea level rise caused by a primary source – melting ice sheets – could prevent widespread flooding, with potentially fewer side effects that may also be fairly localised. Those backing this idea say there are three possible options,
Ice block
The first is to build a 100-metre-tall, 5-kilometre-long submerged wall in front of the Jakobshavn glacier in western Greenland. One of the fastest-moving ice masses on Earth, the glacier could contribute up to 20 centimetres to global sea levels by 2100. The idea is that the wall would block from reaching, and eroding, the glacier at its base.
Another option – more challenging and costly – is to prop up the major floating ice shelves of Pine Island and Thwaites glaciers, among the fastest melting in Antarctica. Together, these glaciers act as a plug for the West Antarctic ice sheet, the loss of which could raise seas by several metres, swamping shorelines across the planet.
Pinning the ice shelves in place using a series of artificial islands or walls connected to the seabed where the ice meets the water could ground the glaciers, slowing ice loss by as much as 80 per cent for Thwaites glacier, say the scientists.
The third option, perhaps the simplest in engineering terms, is to dry out the beds of the fastest-flowing glaciers in Greenland and Antarctica. These shunt 90 per cent of glacial ice to the ocean. Drilling holes in their beds or freezing the meltwater would remove liquid water that lubricates and speeds ice flow above.
Initial results from computer simulations – presented in Vienna – show that each of the three strategies could delay sea level rise for centuries. As appealing as that is, there would probably be unintended consequences, perhaps to ecology, fisheries or even the ice caps themselves. One possibility is that water trapped in pockets at the base of a glacier could speed, rather than slow, its flow.
Most of the unwelcome impacts would be restricted to areas where such schemes are introduced, which sets them apart from the wider potential side effects of most other geoengineering options. But their potential to curb the damage from climatic warming would also be more limited. These approaches may keep millions safe from rising seas, but they will do nothing to stop people from dying in overheated cities or having their homes destroyed by forest fires or inundated by flash flooding.
Sadly, we’re in no position to dismiss targeted geoengineering. Having failed to alter our own behaviour, we must now be willing to consider any route to minimise the damage from climate change – even those that involve altering Earth’s most pristine environments.
Read more: Unstable Greenland glacier is speeding up and draining more ice; Major Antarctic ice survey reveals dramatic melting; Sea-level rise may displace 13 million people in the US by 2100
