Reconstructed temperature, Central Greenland. Source: Giorgiogp2, http://upload.wikimedia.org/wikipedia/commons/2/2d/Greenland_gisp2_alley.png. Licensed under the Creative Commons Attribution-Share Alike 3.0 Unported licence.
We hear all the time about climate change and the impact it may have on the planet as the years go on. Previous climate change events have demonstrated just how rapidly things can change. Few climate change events were as sudden or as impactful as the event that took place around 6200 BC, imaginatively known as the 8.2 kiloyear event. The event was part of a once-every-1 500-year-cycle of climate changes based out of the North Atlantic known as Bond events.Unlike the event taking place currently, major cooling took place during this time. As evidenced in ice cores taken from central Greenland, conditions in the northern hemisphere became colder and drier, especially in winter. Temperatures dropped anywhere from 1-6°C. The cause? The massive emptying of ancient lakes Agassiz and Ojibway into the Atlantic Ocean; in other words, melting ice caused by a global warming trend.
Agassiz and Ojibway were immense proglacial lakes formed by melting waters from the immense continental ice sheet that covered North America during the last ice age. As the sheets melted, lakes formed at their feet, growing as the sheets retreated northward. Eventually, the ice sheet retreated far enough north that the waters of the two lakes came into contact with Hudson Bay. As there was a 250-metre difference in elevation between the lakes and Hudson Bay, once the wall of ice separating the bodies of water from the bay broke, the lakes drained away into the ocean. The two lakes were so immense that the volume of water release caused global sea level to permanently rise as much as 1.2 metres. The sudden influx of cold, fresh water also disrupted the earth’s thermohaline circulation (i.e. the interconnected flow of ocean currents around the world), stopping it dead in the North Atlantic. With no current to bring in warmer water from the south, heat and moisture transport in that part of the world stopped.
We actually owe much today to this cooler, drier period in history: the arid drought conditions produced in the Middle East forced the genesis of irrigated agriculture, and thus the establishment of Mesopotamian civilisation (and thus urban settlement, and literacy, and class separation). It may have also played a huge role in mythology and religion; the global sea level rise may have been responsible for the flooding of the Black Sea basin with saltwater, and the resultant inundation of the surrounding land has been hypothesised by some researchers to be the foundation of the Noah’s Ark myth, among others (though other researchers state that the Black Sea flood wasn’t nearly that catastrophic). One can only guess what the earth may look like after our current period of warming.
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