Climate change factors and thermohaline circulation

In addition to increased levels of atmospheric CO2, we have been introduced to several factors that will contribute to future climate change (see Climate Change: The Science from the University of Exeter). These include: 1) increased levels of atmospheric methane from decomposition of old organic matter with thawing permafrost regions; 2) reduction in the extent of the Amazon rain forest; 3) melting of the West Antarctic ice sheet enhancing the ice-albedo feedback loop and further increases of sea level; and 4) disruption of the Atlantic Thermohaline Circulation that moderates temperatures in north Atlantic and coastal regions of Europe.

The thermohaline current stretches across the globe as shown below. 

(Robert Simmon, NASA. Minor modifications by Robert A. Rohde also released to the public domain - NASA Earth Observatory, Public Domain, https://commons.wikimedia.org/w/index.php?curid=3794372)

The warm waters of the Gulf Stream flow along the east coast of North America into the north Atlantic into areas bordering Greenland, Iceland, Norway and the UK. As this stream cools it sinks and flows down and southward along the ocean floor into the Antarctic region. The melt of sea ice in the north polar region releases fresh water into the surrounding areas. The thermohaline current is salty and heavier than fresh water that may override it and disrupt its flow. A shift in the thermohaline current could result in significant cooling in north Atlantic regions. The decline in the strength of this thermohaline current is believed to have produced significant temperature decline over much of the temperate northern hemisphere from about 12,900 to 11,700 BP [https://en.wikipedia.org/wiki/Younger_Dryas]. An unexpected weakening of the current in 2013 is believed to have resulted in the quietest hurricane season since 1994 [https://en.wikipedia.org/wiki/Thermohaline_circulation] illustrates its ability to have short term impacts as well.