New insights into the dynamics of past climate change 

A new study by the University of Cambridge ‘finds’ (their word) that changing climate in the polar regions can affect conditions in the rest of the world far quicker than previously thought. The full paper has paywalled access only, but by their own admission they say they are ‘only beginning to understand’ the processes they believe they have found.

A new study of the relationship between ocean currents and climate change has found that they are tightly linked, and that changes in the polar regions can affect the ocean and climate on the opposite side of the world within one to two hundred years, far quicker than previously thought.

The study, by an international team of scientists led by the University of Cambridge, examined how changes in ocean currents in the Atlantic Ocean were related to climate conditions in the northern hemisphere during the last ice age, by examining data from ice cores and fossilised plankton shells. It found that variations in ocean currents and abrupt climate events in the North Atlantic region were tightly linked in the past, and that changes in the polar regions affected the ocean circulation and climate on the opposite side of the world.

The researchers determined that as large amounts of fresh water were emptied into the North Atlantic as icebergs broke off the North American and Eurasian ice sheets, the deep and shallow currents in the North Atlantic rapidly slowed down, which led to the formation of sea ice around Greenland and the subsequent cooling of the Northern Hemisphere. It also strongly affected conditions in the South Atlantic within a matter of one to two hundred years.

The results, published in the journal Nature Geoscience, show how climate events in the Northern Hemisphere were tightly coupled with changes in the strength of deep ocean currents in the Atlantic Ocean, and how that may have affected conditions across the globe.

During the last ice age, which took place from 70,000 to 19,000 years ago, the climate in the Northern Hemisphere toggled back and forth between warm and cold states roughly every 1000 to 6000 years. These events, known as Dansgaard-Oeschger events, were first identified in data from Greenland ice cores in the early 1990s, and had far-reaching impacts on the global climate.

The ocean, which covers 70% of the planet, is a huge reservoir of carbon dioxide and heat. It stores about 60 times more carbon than the atmosphere, and can release or take up carbon on both short and long timescales. As changes happen in the polar regions, they are carried around the world by ocean currents, both at the surface and in the deep ocean. These currents are driven by winds, ocean temperature and salinity differences, and are efficient at distributing heat and carbon around the globe.

Ocean currents therefore have a strong influence on whether regions of the world are warm (such as Europe) or whether they are not (such as Antarctica) as they modulate the effects of solar radiation. They also influence whether CO2 is stored in the ocean or the atmosphere, which is very important for global climate variability.

“Other studies have shown that the overturning circulation in the Atlantic has faced a slowdown during the last few decades,” said Dr Julia Gottschalk of Cambridge Department of Earth Sciences, the paper’s lead author. “The scientific community is only beginning to understand what it would mean for global climate should this trend continue, as predicted by some climate models.”

Full report: New insights into the dynamics of past climate change | University of Cambridge

Study: Abrupt changes in the southern extent of North Atlantic Deep Water during Dansgaard–Oeschger events