Terrance Joyce, who chairs the Woods Hole Physical Oceanography Department, believes that the atmospheric cooling caused by a thermohaline circulation shutdown could begin as soon as 2012. Joyce believes that once it does, it could take hundreds of years to reverse. In a recent letter to The New York Times, he challenged readers to recall the coldest winters in the Northeast, like those of 1936 and 1978 and then imagine recurring winters that are even colder—that would be what such a "little ice age" would feel like.
A 5- to 10-degree drop in temperature could have devastating ecological and economical effects. The National Academy of Sciences (NAS), in a recent article titled "Abrupt Climate Change: Inevitable Surprises," reports that the cost from agricultural losses alone could reach $100 billion to $200 billion and that damage to ecologies could be "vast and incalculable." NAS predict accelerated species extinctions, disappearing forests, low crop yields, inflated housing costs, and dwindling freshwater. The faster the climate change is, according to most predictions, the more dire the consequences will be.
Another prevailing concern is the effect a little ice age would have on the world's poor. In a modern world with closed borders, those living in drastically changing climates would not have the option to simply pick up and move south like ancient tribes did during previous cooling periods. According to the NAS report, "To the extent that abrupt climate change may cause rapid and extensive changes of fortune for those who live off the land, the inability to migrate may remove one of the major safety nets for distressed people."