Melting Scandinavian glaciers made Europe cool and dry

A combination of old midges and climate modelling suggests that melting ice sheets in Scandinavia triggered a dramatic 1000-year long cold snap in Europe, 12,800 years ago. (Photo: Flickr Vincent Moschetti)


  • A cold event 12,800 years ago plunged Europe back into near Ice Age conditions, but scientists could not fully explain what had triggered it.
  • New evidence confirms that melting glaciers in Scandinavia were the likely trigger.
  • The melt water allowed summer sea ice to spread, and accounts for the timing and nature of this severe 1000-year long cold snap.
  • The results explain one of the dramatic climate events in Earth’s history and raises fresh concerns for European climate as glaciers continue to melt today.

Temporary and extreme climate changes punctuated the warming of the Northern Hemisphere, as the Earth escaped the icy grip of the last Ice Age.

One such event occurred 12,800 years ago–the so-called Younger Dryas–when Europe was suddenly plunged back into near-Ice Age conditions. The ensuing cold struck the northern hemisphere quickly, and hard. But how and why remained a mystery.

Now, a new study claims to have an answer: A combination of old midges and climate modelling suggests that melting glaciers in Scandinavia set in motion the key changes necessary for this dramatic cold snap to occur.

“The melting of the Scandinavian ice sheet is the missing link to understanding […] the response of the North Atlantic system to climate change,” says lead-author Francesco Muschitiello from Stockholm University, Sweden, in a press release.

The results are published open-access in the journal Nature Communications.

A who dunnit of climate science: America or Scandinavia?

The so-called Younger Dryas–an approximately 1000-year long cold snap–would certainly take Northern Europe by surprise today.

Many scientists assumed that melting of the great ice-sheets in North America at the end of the last Ice Age were responsible, as they disrupted ocean currents, cutting off Northern Europe’s supply of warm water and with it warm air from the tropics, via the Gulf Stream.

 

Vast quantities of cold fresh water that ended up in the Nordic Seas, allowed summer sea ice to spread out. This drastically affected the local climate, sending cold and dry air over Scandinavia, whilst Greenland started to experience relatively warmer and wetter conditions. (Photo: Flickr Béatrice Karjalainen)

Vast quantities of cold fresh water ended up in the Nordic Seas and allowed summer sea ice to spread. This drastically affected the local climate and sent cold and dry air over Scandinavia, whilst Greenland became relatively warm and wet. (Photo: Flickr Béatrice Karjalainen)

But the timing of this melt does not quite fit with the timing of the onset of this cold snap across Greenland and much of Europe. Some scientists suggested that the culprit lay closer to home, and that melting glaciers in Scandinavia could have been the trigger. But they did not have the evidence to show precisely how this could work.

The new study has some answers.

Midges record summer temperatures

They analysed the chemistry of the remains of midges from an ancient lake in southern Sweden. The midges recorded summer temperatures in the lead up to, and throughout, the Younger Dryas cold snap.

“The remains of midges, contained in the lake sediments, reveal a great deal about the past climate,” says co-author Steve Brooks, from the Natural History Museum, UK, in a press release.

“The assemblage of species [..] enable us to track how, after an initial warming of up to 4 degrees centigrade at the end of the last Ice Age, summer temperatures [in Scandinavia] plummeted by 5 degrees centigrade over the next 400 years,” he says.

Crucially, these changes also matched the sequence of events recorded in the Greenland ice cores over the same time. But with a catch: As The Younger Dryas started to kick in, Scandinavia became cold and dry whilst Greenland experienced a short reprise of relatively warmer and wetter climate, before also becoming cold and dry.

Climate models explain what is going on

So, what exactly was going on? Muschitiello and his team turned to climate models for some answers.

They tested whether a sophisticated climate model could first of all, accurately predict the observed climate data–which in this case comes from the chemistry of the midge remains and the chemistry of the Greenland Ice cores.

They set up a scenario within the model whereby initial warming across Scandinavia triggered the ice-sheets to start melting, which sent vast quantities of freshwater into the North Sea.

With this in place, not only did the climate model accurately predict the warm and wet conditions over Greenland and the cold and dry conditions in Scandinavia, it told the scientists why the climate responded in this way.

According to Muschitiello, the vast quantities of cold fresh water that ended up in the Nordic Seas, allowed summer sea ice to spread out. This drastically affected the local climate, sending cold and dry air over Scandinavia, whilst elsewhere, Greenland was experiencing relatively warmer and wetter conditions.

The new results offer a convincing explanation for how the onset of this dramatic climate event played out throughout the Northern Hemisphere and provides a crucial understanding of how and why melting of ice-sheets in Scandinavia can lead to rapid and dramatic local changes in climate. [wp-svg-icons icon=”mug” wrap=”i”]

 

Photo Credit: Vincent Moschetti

 

Time for a bit more? Read on…

Looking for more reading on this topic? First off, why not try reading the original open-access scientific article.

If that is a step too far, then try the original press release form EurekAlert.

Check out the scientists Francesco Muschitiello’s research profile to read about his research interests.

 

ResearchBlogging.org

Muschitiello, F., Pausata, F., Watson, J., Smittenberg, R., Salih, A., Brooks, S., Whitehouse, N., Karlatou-Charalampopoulou, A., & Wohlfarth, B. (2015). Fennoscandian freshwater control on Greenland hydroclimate shifts at the onset of the Younger Dryas Nature Communications, 6 DOI: 10.1038/ncomms9939

 

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