The Change Of The Thermohaline Circulation

This news article in the Washington Post highlights the issues of an arguably changing thermohaline circulation around the planet. It has effects on the melting (or crumbling as my blog title describes) cryosphere and the melting ice at the poles in particular can have an impact on the thermohaline circulation. The thermohaline circulation is a global cycle of water whereby warm water rises at the equator and then sinks as colder saline water at the poles.
Figure 1: NADW stands for North Atlantic Deep Water. This is by Stefan Rahmstorf's at the Potsdam Institute for Climate Impact Research (source).


A new study by Stefan Rahmstorf has observed a slowing of the thermohaline circulation. He argues that the North Atlantic ocean is cooling from a reduction of the Atlantic meridional overturning circulation (AMOC) despite the rest of the planet warming due to global warming. I agree that the North Atlantic has cooled as temperature studies have shown but its cooling is not enough to cause a reduction of the Gulf Stream which gives western Europe milder weather than the latitude would otherwise offer. A paper by Vellinga and Wood on the Global Climatic Imapcts Of a Collapse Of The North Atlantic Thermohaline Circulation explains that the North Atlantic temperature has decreased by 1-2 degrees C.







If the Greenland ice sheet melts to a high degree, the freshwater produced will freshen the cold saline water and make the water less salty which will in turn lessen the density of the water which will cause less to sink. This will cause a slowing of the circulation as explained in Rahmstorf''s article.

Figure 2: This is the global model of ocean temperature change in 2014/2015 showing the record coldest temperature in the North Atlantic (source).
Figure 3: This is the temperature change between 1901 and 2000 (source). This again shows cooling of the North Atlantic despite everywhere else warming.
A warming of the oceans could cause a reduction of the Gulf Stream which would cause cooler climates in western Europe. Further melting of the Greenland ice sheet in the future could contribute to further weakening of the AMOC.
The thermohaline circulation warming will accelerate thermal expansion of the oceans which will cause as positive feedback, melting the polar ice sheets due to warmer oceans. The albedo effect as explained in an earlier post would then enhance global warming.
This video illustrates the global ocean conveyor (thermohaline circulation) from Youtube.
The next post will focus on the melting of the Antarctic ice sheet and its possible impacts on both physical and human geography.

Effects Of The Albedo Effect

The paper published by Pistone et al in 2014 gives a numerical insight into the albedo effect and its influence on the melting polar ice sheets. The albedo effect is how much sunlight is reflected by a particular material such as ice or sea. All objects have an albedo score between 0 and 1. The darker an object, the more sunlight energy is absorbed and conversely the lighter an object, the more light energy is reflected. The paper by Pistone is informative and shows that the albedo in the Arctic has decreased from 0.52 to 0.48 W/m2 from 1979 and 2011.
Ice is white and therefore reflects most of the sun's energy and has a high albedo. At the poles, light is reflected by the ice sheets and gives a cooling effect. However with global warming, the cryosphere is melting which reduces the amount of ice present at the poles. More dark sea is exposed which has a much lower albedo. Having a lower albedo, more of the sun's energy is absorbed which produces a positive feedback effect where by the dark sea becomes warmer which in turn enhances global warming through thermal expansion of the oceans.
Figure 1: This image taken from Pistone's 2014 paper illustrates the melting of the Arctic sea ice in picture C between 2007 and 2011 (source).
Consequently, the image in D shows a lower albedo where the dark sea absorbs the sun's energy, lowering the albedo. These images show that the cryosphere is indeed melting. As 97% of all climate scientists believe that anthropogenic global warming is taking place, the albedo effect will be a major factor in the control of feedback mechanisms that can control global warming.


For humans, the positive feedback mechanism is not a short term change but long term. The effects will not be sudden but will happen over time. The main impact on humans are the rising sea levels which are produced by thermal expansion due to a lower albedo producing enhanced global warming.


The next post will focus on the thermohaline circulation and its effects on the melting cryosphere.

Melting Permafrost

(First see the post titled 'Introduction To The Crumbling Cryosphere before reading this post)
An interesting article on the melting permafrost from the BBC. I feel that Professor Vladimir Romanovsky is right saying that the permafrost in Alaska will start to thaw by 2070. The permafrost is permanently frozen soil that does not melt during the summer and that has been frozen for more than 2 years. The melting of the permafrost could have serious consequences.
Worryingly, there is undersea permafrost that contains large amounts of methane is starting to melt, particularly in Siberia. As methane is approximately 20 times more potent than carbon dioxide as a greenhouse gas, the more released from melting permafrost, the more global warming is enhanced. The Arctic sea ice and the Greenland ice sheet melting will be increased along with areas of Antarctica suffering record ice loss.
Figure 1: This image is from the National Snow and Ice Data Centre and shows the average amount of sea ice surrounding the polar regions (source). The sea ice cover in the spring and autumn months (September in the Arctic and March in the Antarctic) is minimal and future summers could lead to ice free poles. It is debated among climate scientists when exactly the Arctic could become ice free.
For humans, the Northwest Passage becoming ice free in the future could mean a quicker and more convenient shipping route to the Asian markets. However, a changing climate could mean that melting glaciers that provide drinking water to millions of people could disappear with the melting cryosphere.