As is well known to students of the history of the climate, once a temperature threshold is breached, abrupt weather events ensue amplified by feedbacks such as decreased reflectivity of the Earth surface and enhanced release of greenhouse gases, often within short time frames.
Such abrupt changes are occurring at present. As mean global temperature has exceeded 1.2 degrees Celsius above 1880 temperatures (Figure 1), sharp reductions occur in Arctic sea ice from 45 percent in 1985 to 21 percent in 2017[i], when the ice cover was 8.5 percent lower than the average of 1981-2010[ii].
As the ice melts the near-total reflection (high albedo) of solar radiation from the ice is replaced by absorption of infrared radiation by open water; The flow of ice-melt water from the Greenland glaciers creates a large pool of cold water in the North Atlantic Ocean. The cold water region south of Greenland slows-down to aborts northward flow of the thermohaline Atlantic Meridional Ocean Circulation (AMOC), leading to cooling of the North Atlantic and adjacent North America and Europe[iii].
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