Focusing their attention on the collapse of the Barents ice sheet which took place some 140,000 years ago, scientists from Bangor University and the University of Sheffield have used a computer climate model to understand how different states of freshwater entering the oceans affect the circulation of the oceans.
“Freshwater entering the ocean from melting ice-sheets can weaken the climate controlling part of the large-scale ocean circulation, with dramatic climate change as a consequence,” explains co-author Dr Mattias Green, a Senior Research fellow at Bangor University’s School of Ocean Sciences. “During the period of our study, the global temperature dropped by up to two degrees over a few centuries, but changes were not uniform over the planet, and it took a long time for the climate to recover after the ice sheets had melted completely.”
But the real issue, according to the scientists, is not how much freshwater is released into the oceans from a melting ice-sheet, but rather the manner in which it enters the oceans: specifically, while icebergs which calve off a melting ice-sheet affect the ocean circulation less than does meltwater, an iceberg will last for a much longer time.
“This can be compared to the difference between adding very cold water to your drink, or adding an ice cube or two,” explains Mattias
“With meltwater – similar to adding water to your drink – the water spreads out quickly and has an immediate effect, but it is also absorbed quickly into the rest of the ocean. In a similar way to your ice cube, the icebergs drift along and melt more slowly. This means the immediate impact is weaker, but they are there for a longer time and distribute the water over a larger area.”
The scientists also deduced that the planet’s oceans 140,000 years ago reacted differently to an ice-sheet collapse than they would 120,000 years later, during the much more studied ice age which took place 20,000 years ago. According to the scientists, the oceans were more sensitive to ice-sheet collapse during the more recent ice age than they were in the past.
“Our results lead us to conclude that a future ice-sheet collapse, that might happen in Antarctica or Greenland, would have climatic consequences, but the exact impact needs to be evaluated in each case,” added Mattias.