The melting of Antarctic ice sheets is one of the most visceral consequences of climate change, but the full extent of their impact on the cycle remains mostly unknown. Now, researchers from the US and South Korea have run climate simulations that include the "iceberg effect" and found that melting icebergs could play a significant role in slowing warming in the Southern Hemisphere.
Over the last century or so Antarctica has been shrinking at an alarming rate – and it's speeding up, with rates of ice loss tripling since 2012. As huge icebergs break away from the mainland, they tend to destabilize the remaining ice shelves, and it's now thought that a quarter of the glacier ice in West Antarctica is unstable. But once they drift away from the continent, what effects do the icebergs have on the climate as a whole?
Much of our understanding of climate change comes from models and simulations, but there are just so many factors at play that it's incredibly difficult to account for all of them. What effect does the greening of Antarctica have? How about the hole in the ozone layer? Or even the speed at which the bedrock is rising?
And of course, there's the icebergs themselves. As they melt, they cool the ocean water they're floating in, and dilute it, lowering the salinity of the ocean. What effects this process might have on climate change itself was the focus of the new study, involving researchers from the Universities of Hawaii, Massachusetts and Penn State in the US, and the IBS Center for Climate Physics in South Korea.
The team ran several computer simulations that modeled global warming, complete with a virtual Antarctica that released icebergs at a realistic rate, number and sizes over a few hundred years. But there was one major new factor not previously accounted for – the combined effects of cooling and salinity-lowering these icebergs would have on seawater.
The researchers switched this iceberg effect on and off in their climate model, and sure enough, they found that in the models with the iceberg effect on, human-induced warming was significantly slowed. That in turn affected global winds and rainfall patterns.
"To melt the icebergs released over the 21st century in one of our extreme Antarctic ice-sheet retreat scenarios would require 400 times the current annual world energy consumption," says Tobias Friedrich, co-author of the study. "Global sea level would rise by about 80 cm (31.5 in), impacting many coastal regions and communities worldwide."
Interestingly, this conclusion goes against a previous study that found that melting glaciers actually speed up further melting in a vicious cycle. But, the team says, both could be different parts of the same complex system, and they may even roughly cancel each other out.
The main conclusion is that melting icebergs are a major factor that may not yet be under consideration in many models. That includes the latest assessment by the Intergovernmental Panel on Climate Change (IPCC).
"Our research highlights the role of icebergs in global climate change and sea level rise," says Axel Timmermann, corresponding author of the study. "Depending on how quickly the West Antarctic ice sheet disintegrates, the iceberg effect can delay future warming in cities such as Buenos Aires and Cape Town by 10 to 50 years."
In future the team plans to use a new computer model to further investigate the effects of ice on the changing climate.
The research was published in the journal Nature Climate Change.
Source: Institute for Basic Science
