There are many unknowns when it comes to climate change, like what might happen to the ice in Antarctica. Vast and remote, this continent holds many mysteries, like the rivers and lakes that sit underneath the massive ice sheet covering the land. This watery layer could help move ice sheets toward the ocean, and scientists have been trying to understand the forces that are at work as glaciers melt. Research has now shown that the subglacial waters of Antarctica have a larger impact on the ice that we previously knew. The study authors suggested that this water under the ice needs to be taken into account in models of sea level rise, which might now be vastly underestimated. The work has been reported in Nature Communications.
When subglacial water is factored into ice sheet models, the amount of ice flowing into the ocean can triple, which increases sea level rise by the year 2300 by two meters. If that happened, there would be a much larger impact on coastal communities, and it's estimated that about 1 billion people within 10 kilometers (6.2 miles) of a coast.
The base of an ice sheet can melt due to geothermal heat coming up from below, or because of friction from ice movement. That subglacial water lubricates the sheet, allowing it to move easily over bedrock, which drives more melting, and increases the loss of ice in a feedback loop.
This subglacial water is hard to study though, because it's hidden away under ice sheets, some of which are over two kilometers deep. To study these waters, scientists have to perform complex and costly fieldwork in which drills are used to take samples from deep within the ice.
Other technologies like radar that penetrates the ice, or laser altimetry, which detects changes in height from the surface, can also be used.
In the past two decades, these efforts have revealed over 140 active Antarctic subglacial lakes. But there are still large areas about which little is known.
In this study, the researchers used computer models and simulations to make predictions about ice sheet behavior and how it was affected by subglacial waters and pressure. One model focused on flow of the ice sheet while another focused on the volume and flow of the subglacial water.
As subglacial water pressure was factored in, the movement of ice into the ocean got almost three times bigger. As such, the study authors suggested that current estimates of sea level rise may be too low.
This work may also indicate that other tipping points in the climate have also been underestimated. (A tipping point has been defined as a point at which critical thresholds are crossed, and a system is reorganized, "often abruptly and/or irreversibly.”) This work has suggested that some tipping points may be crossed by 2050.
The researchers also noted, however, that this system is complex and difficult to understand. There is still the potential for a catastrophic loss of ice in Antarctica, and more work will be needed to make better predictions about how the ice sheet will behave in the future, and how it will impact sea levels.
Sources: Phys.org via The Conversation, Nature Communications
