The event may have been caused by a large meltwater pulse from the final collapse of the Laurentide Ice Sheet of northeastern North America, most likely when the glacial lakes Ojibway and Agassiz suddenly drained into the North Atlantic Ocean. The same type of action produced the Missoula floods that created the Channeled scablands of the Columbia River basin. The meltwater pulse may have affected the North Atlantic thermohaline circulation, reducing northward heat transport in the Atlantic and causing significant North Atlantic cooling. Estimates of the cooling vary and depend somewhat on the interpretation of the proxy data, but drops of around have been reported. In Greenland, the event started at 8175 BP, and the cooling was 3.3 °C (decadal average) in less than 20 years. The coldest period lasted for about 60 years, and its total duration was about 150 years. The meltwater causation theory is, however, thrown into speculation because of inconsistencies with its onset and an unknown region of impact.