One of the great mysteries of late medieval history is why did the Norse, who had established successful settlements in southern Greenland in 985, abandon them in the early 15th century? The consensus view has long been that colder temperatures, associated with the Little Ice Age, helped make the colonies unsustainable. However, researchers just discovered that it wasn’t dropping temperatures that helped drive the Norse from Greenland: it was drought.
Almost a thousand years later, it appears that history is repeating itself. Today, in the Amazon, rain forests could be at a far higher risk of extreme drought than previously thought. Much like Greenland’s ancient Vikings, will those who now live in the Amazon region soon be driven from their homelands because of too-dry conditions?
Why the Vikings left Greenland
When the Norse established the Eastern Settlement in Greenland in 985, they thrived by clearing the land of shrubs and planting grass as pasture for their livestock. The population of the Eastern Settlement peaked at around 2,000 inhabitants, but it collapsed quickly about 400 years later. For decades, anthropologists, historians and scientists have thought that the Eastern Settlement’s demise was due to the onset of the Little Ice Age, a period of exceptionally cold weather, particularly in the North Atlantic, that made agricultural life in Greenland untenable.
Before a recently conducted study, led by researchers from the University of Massachusetts Amherst and published in the journal Science Advances, there was no temperature data from the Eastern Settlement site. Instead, ice-core data that previous studies had used to reconstruct historical temperatures in Greenland was taken from a location that was more than 620 miles to the north and more than 6,500 feet higher in elevation. The University of Massachusetts Amherst scientists sought to study how climate had varied in locations closer to the Norse farms. And when they did, the results were surprising.
The scientists traveled to a lake called Lake 578, which is adjacent to a former Norse farm and close to one of the largest groups of farms in the Eastern Settlement. There, they spent three years gathering sediment samples from the lake, which represented a continuous record for the past 2,000 years. No one had studied that location before.
The researchers then analyzed the samples for two different markers: the first, a lipid, known as BrGDGT, which can be used to reconstruct temperature. A complete record can directly link the changing structures of the lipids to changing temperatures. A second marker, derived from the waxy coating on plant leaves, can be used to determine the rates at which the grasses and other livestock-sustaining plants lost water due to evaporation. It is, therefore, an indicator of how dry conditions were.
What the scientists discovered is that while the temperature barely changed over the course of the Eastern Settlement of southern Greenland, it became steadily drier over time. Norse farmers had to overwinter their livestock on stored fodder; and even in a good year, the animals were often so weak that they had to be carried to the fields once the snow finally melted in the spring. Under conditions like that, the consequences of drought would have been severe. An extended drought, on top of other economic and social pressures, may have tipped the balance just enough to make the Eastern Settlement unlivable.
This study changes our understanding of early European history and highlights the importance of continuing to explore how environmental factors influence human society.
How unchecked climate change will cause severe drying of the Amazon Rain Forest
Fast-forward to today in the Amazon Rain Forest, and something similar could be playing out.
The vast Amazon Basin (or “Amazonia”) is an area of about 2.7 million square miles—roughly the size of the land in the 48 contiguous United States—and covers about 40 percent of the South American continent. It’s home to the largest tropical rain forest on Earth and plays a key role in global carbon and water cycles. The basin includes parts of eight South American countries: Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname and Venezuela; and French Guiana, a territory of France. Made up of a mosaic of ecosystems and vegetation types—including deciduous forests, flooded forests, rain forests, savannas and seasonal forests—the Amazon Basin reflects conditions in a wide range of environments, as well as human influence.
Existing climate models disagree on whether Amazonia will become drier or wetter. This makes it difficult for policymakers to predict future droughts, assess wildfire risks, or plan climate change mitigation and adaptation strategies.
So, recently, a research team, led by scientists from England’s University of Leeds, examined factors regulating the process by which forests transfer water from the soil to the atmosphere, known as evapotranspiration. They analyzed the results of 38 known Amazon climate models. According to their study, published in the journal Environmental Research Letters in July 2021, only a third of the 38 models correctly reproduced the interactions between the atmosphere and land surface previously shown by Amazon fieldwork.
By ruling out climate predictions from unrealistic models, the uncertainty in rainfall changes over the whole Amazon basin was reduced by half. The remaining models showed wide agreement in predicting future rainfall changes, with severe drying expected in the eastern Amazon over the next 80 years, and, conversely, rainfall increases in the western basin.
The increased dryness during the Amazon dry season would further threaten the viability of large parts of the rain forest, as trees are already water-stressed and there is greater risk of forest fires. As a result, large amounts of carbon dioxide would be released from the forest into the atmosphere, adding to the greenhouse gas effect and driving further climate change.
The predicted droughts could also have far-reaching consequences for the Amazon’s biodiversity, water cycle and the people who live in the region.
These findings predict reductions in rainfall that are comparable to the drying seen during the major droughts of 2005 and 2010, which caused widespread tree mortality and had major impacts for Amazon communities. People in Brazil and across the globe are rightly concerned about what the future holds for the Amazon and its valuable store of biodiversity and carbon.
When once the land was green
On Sunday, September 16, 1408, Sigrid Bjornsdottir wed Thorstein Olafsson. The couple had been sailing from Norway to Iceland when they were blown off course. They ended up settling in Greenland, which by then had been a Viking colony for around 400 years. Their marriage was mentioned in three letters written between 1409 and 1424. Those letters were the last anyone ever heard from the Norse Greenlanders.
It seems that they vanished from history.
I hope that hundreds of years in the future, Amazonia as we know it hasn’t succumbed to climate change, deforestation and drought. Today, we know how to protect and expand existing forests so that they can absorb and store more carbon, slowing down—even if not ending—climate change.
I also hope that future historians, hundreds of years from now, won’t find a few, last mentions of a vast, emerald-green rain forest, where what they then look upon is only a vast basin of dust.
Here’s to finding your true places and natural habitats,