Thermohaline and Sea Ice. Tipping points become blurry,

Reaching a tipping point within the thermohaline would be manifested as a continual decrease on the strength of the overturning current. Arctic sea ice once more plays a part in the perpetuation of a slowing circulation. Not only does it drive the slowing but is also advanced by the slowing. This positive feedback loop can be manifested in many ways but most notably by a decline in ocean heat distribution as well as the previously noted increase in sea ice and Greenland ice sheet melt.

Firstly, it is important to acknowledge a noticeable increase, during the past century, in the overall temperature of the planets oceans. Given the intrinsic properties of the thermohaline circulation an overall and generalised increase will not fundamentally adjust the system.

However, our interest lies in a shift in the distribution of heat within the global oceans. As visible in Figure 2, the North Atlantic has traditionally been warmer than other areas as a result of the gulf stream carrying heat energy north. Contradictory to the idea that thermohaline is slowing as a result of climate change, the image below shows a consistent trend in North Atlantic warmth ceetaintly not weaking up intil 2005. However, it does also reinforce the general warming trend of the last century.

The last time arctic sea surface temperatures were at a similar level to today, 2016, was during the Eemian Period or the last inter-glacial. However during this period a vast melting occurred causing extreme storms and sea levels, 5 to 9 m higher than today. There is one massive difference between that period and today however, and that is carbon diodixe levels. During the last inter-glacial CO2 levels we significantly under 300ppm yet in 2016 for the first time in history CO2 levels rose above 400ppm without dipping below, and will probably not for the foreseeable future. The last inter-glacial the colder winters hindered the massive ocean temperature rise. However signifcant sea ice melt experienced at present as well as black carbon deposits covering the remaining ice sheets may well increase the temperature to an unsustainable point.

In NASA’s temperature data is embedded a polynomial trendline which points at temperature anomolies of over 4^oC by 2060. A worse case arises when analysing the polynomial trendline in the Arctic which predicts temperature anomolies of over 4°C by 2020, 6°C by 2030 and 15°C by 2050. It is in this scenario where feedback mechanisms could easily bring about abrupt climate change.

Questions posed by a slowing therrmohaline include a cooling of the Arctic as a result of slowing. Disregarding the global climate changes and potential extreme methane releases, a reduction in heat flowing north would restrict the warming of arctic waters and hence reduce ice melt, therefore restricting the decrease in salinity and the slowing of the meridional overtunring circulation. This is where the holistic nature of climate systems begin to blur the simplicity of a tipping point. The major tipping point is yet to be found but any combination of these may trigger an extreme event and abrupt change.