Concluding Remarks

Upon starting this blog, I was fairly convinced that we were to experience tipping points, or have already reached one, within the Arctic system and that these posed a significant threat to the stability of our planet. This belief may have been as a result of media influence with all major news outlets noting the ‘impending doom spiral’ in the Arctic. However, upon the journey of the blog I found that the likelihood of a tipping point, especially in regards to sea ice, is extremely low. The counter-acting forces of the different systems supporting one another takes away the sea ice’s ability to experience a rapid decline. In terms of a regime shift it is almost unquestionable that we have experienced one in the Arctic ocean, a shift to ice-free summer exemplifies these changes, fortunately it can sustain itself in several climates and so may re-stabilise one it reaches seasonally ice free state. The biggest threat in the next several centuries comes from the Greenland Ice Sheet and the Arctic Meridional Overturning Circulation. As it transpires, a significance discharge of icebergs from the sheet can cause such a large freshwater influx it can cause the shutdown of the global ocean conveyor. The likelihood of this happening in our lifetime is minute, however, it may pose a threat to future generations.

As a planet it is imperative that we continue the plan set out in the Paris Agreement, or at least take the first steps towards achieving it. Halting the emissions freight train cannot happen overnight therefore CO2 levels will continue to rise in the atmosphere and global warming will continue, accelerating some of the processes discussed in this blog. Over the past two decades we as a global population have addressed our climate shortcomings with severity and immediacy, as evidenced by the dramatic reduction in aerosol emittance and progress in Asia, China went from having 16 of the top 20 polluted cities global in the late 1990’s to having none, today. Hopefully the new coconscious middle class that is emerging in India will bring about a similar pattern given 12 of the top 20 polluted cities are now in India, although as a nation it has some way to go before it emits anything like the US and other developed nations. The coming months will be telling in our reduction prospects given the current instability in the largest emitter on the planet it yet to be confirmed whether such progress will be continued.

Revisiting the Thermohaline

Initially we spoke rather passively about the effects of climate change on the thermohaline, however, as the blog progressed I realised that the key to abrupt climate change is in fact this system. It has been viewed in sediment records that during the past glacial periods the cooling is incited by a collapse of the thermohaline as a result of warming. The system is vulnerable from both the North and the South. In regards to the reducing sea ice, this directly impacts the system’s ability to function as it reduces the temperature as well as the salinity in the surface water, this is water that is transported North in the Gulf stream and is destined to sink in the Arctic and form the North Atlantic Deep Water current. A similar process is experienced surrounding the Antarctic continent where warming reduces the sea ice and the process is replicated.

As the key to bringing about abrupt climate change it is important to note the causes of such instances. Several readings were conclusive with this citing that large icebergs breaking off the Greenland Ice Sheet caused a rapid freshening of the Arctic surface water completely inhibiting the AMOC and inciting a period of freezing as a result of mis-distribution of the global heat budget allowing it to occur at the poles. Once, this takes hold the albedo feedback becomes relevant once again in reducing the energy absorbed by the planet.

We addressed the likelihood of such an extreme event occurring in the future as a response to anthropogenic forcing and although unlikely were able to conclude that there will be a significant weakening of the system by 2100 on several emission scenarios, this slowing will bring about a degree of heat distribution that will noticeably alter the climate around the world, perhaps significantly.

Revisiting the Arctic

This blog, in essence, is attempting to discuss whether anthropogenic forcing has pushed the Arctic environment to a non-recoverable point, one where it will continually decrease or as a result of reaching a tipping point will succumb to a variety of positive feedback mechanisms and begin to rapidly collapse.

Addressing the situation in the Arctic we identified 4 systems within the Arctic as a whole: Sea Ice, the Greenland Ice Sheet, the Thermohaline Circulation, and the Polar Vortex. In reality only the Sea Ice faced any sort of threat from positive feedback mechanisms.

When first addressed the Sea Ice presented a strong case for succumbing to feedback mechanisms as its daily rate of formation was significantly lower than every previously experienced and resulted in the Sea Ice extent being 400,000km2 lower the previous lowest October formation. However, during December an anomalous rate occurred once again only in the opposite direction, ice was forming at 90,000km2 per day meaning by the close of the year there wasn’t a significant gap between the 2016 and 2017 opening extent, only the expected decrease was observed. This prompted the question of true nature of tipping points within the system and whether they in fact existed. However, before we could answer this question we first needed to understand the feedback mechanisms at play within the system, the major one being the albedo effect. Later on in the blog we visited geoengineering projects that would utilise albedo in order to regain sea ice and lower global temperature, in this instance we can refer to said blog post to validate the albedo effect. It was modelled that by increasing the reflectivity of the local ocean, between 70-90 degrees it will cause cooling such that sea ice would reform and stabilise, this comes as a result of its capacity to function sustainably within different climate settings. The albedo effect then plays a vital function in the stability of the sea ice, the continued loss of sea ice as a result of anthropogenic forcing and global warming causes the increased absorption of energy into the local ocean which is significant enough to cause subsequent melt through rising temperatures. In terms of the further interactions and feedbacks they are all rather negligible in terms of affecting the future situation.

The Greenland Ice Sheet

Perhaps with the greatest potential to incite rapid climate change we examined whether it was being impacted by global warming as severely as the media spreads. Upon discover we found there were areas to be concerned, the functioning of millennial scale process on a decadal once causes slight alarm, however, the sheer mass and volume of the ice sheet insulates itself from any major rapid change instead it will be a continual decrease over the next several hundred years that could well accelerate and flood over 50% of Asia’s population as a result of sea level rise. Apart from this the only cause for concern is that of major icebergs detaching and becoming highly influential in the Arctic Meridional Circulation but that will be discussed in due course. The formation of supraglacial lakes on the Antarctic Ice Sheet is a mirror of the effects felt similarly on the Greenland Ice Sheet, only at a much slower pace. The more rapid pace in the Northern hemisphere could lead to earlier destabilisation of the sheet and encourage the aforementioned ice bergs to break from the main body.

The Polar Vortex

Before we address the complexities of the Thermohaline Circulation lets first revisit the Polar Vortex. Perhaps the most significant in terms of impacting the daily lives of the population, the weakening of the polar vortex causes localised climate change as it lowers the colder temperatures on the Pacific mid-west as well as potentially over Northern Europe. Although this is not necessarily a significant and demanding consequence it is an early example of how warming the Arctic can begin to affect day to day lives.

Just touching base with the polar opposite

The impacts of climate change in Antarctica is relatively neglected in today’s literature and mainstream media in comparison to the Arctic, but why? Is climate change negligible in Antarctica or is the mere scale of the continent mean and effects pass under the wayside.

In fact, the West Antarctic Peninsula is one of the fastest warming areas on the planet with only areas within the Arctic Circle experiencing more rapid heating. However, my earlier proposal in regards to scale is partly accurate. Due to the vastness of the continent the effects of climate change are largely heterogeneous with some areas experiencing the polar opposite to the Arctic, a gain in sea ice extent. If we think back to my previous post regarding the Arctic Meridional Overturning Circulation it was stated there that in fact a warming in the Arctic would lead to a warming in the South as CO2 forcing continued, therefore this wouldn’t come as a surprise. Yet it is not entirely representative. Figure 1 depicts the heating trends over Antarctica between 1981 and 2007, upon first glance it is undoubtedly clear that the majority of Antarctica is experiencing some sort of heating.

Figure 1: Representation of surface temperature change between 1981 and 2007. Credit: NASA 

Beyond regional climate shifts the Antarctica has the potential to influence global climate. Due to the massive ice sheet covering the landmass Antarctica operates as a major heat sink as well as displaying similar characteristics as the Arctic Sea Ice in regards to maintenance of ocean/atmosphere interaction and increasing salinity aiding in the formation of bottom water currents. It also has the potential to slow the thermohaline much like the Greenland Ice Sheet. The combination of a natural variability in the deep ocean adjacent to the ice sheet similar to El Nino/ La Nina but on a centennial scale; and warmer water causing direct melting of the ice sheet below the surface depositing large icebergs into the ocean (Bakker and Clarke, 2016). These combine to cause a large freshwater influx into the surrounding oceans and into the ocean currents, slowing the creation of bottom waters much like the Greenland Ice Sheet in my previous post. One crucial difference is that despite all of this, the influx of freshwater increases the formation of sea ice increasing the albedo of the area and beginning to neutralise the negative impacts on the bottom water. According the NSIDC, 2014 set a new record for maximum sea ice extent, before subsequently returning to average levels.

Figure 2: Satellite image depicting the summer Antarctic sea ice maximum, 2014. Credit: NASA

A subtle contributor to sea level rise?

Annually enough snow is deposited upon the ice sheet is equivalent to a 5mm rise in global sea level, this process is mirrored by the annual discharge of ice back into the ocean. Therefore, a slight imbalance in the inputs and outputs and it may be a major contributor to the rise in sea level experienced today, which currently stands at 1.5-2mm per year. However, the uncertainty is large as our current understanding of the processes in the Antarctic are severely limited.

Possible Weakening of the Ice Shelf?

Supraglacial lakes are revered for their influence on ice melting in Greenland. They are a literally and observable representation of the degree of melt occurring on the surface of the ice shelves, but beyond that they in fact can aid in the breaking up of the sheet. The supraglacial lakes can flow vertically down through the ice weakening its structure while at the same time lubricating the surface below allowing for large icebergs to break off more easily. A recent study found that during the summer months between 2000 and 2013, 8000 of these supra glacial lakes have formed on the Langhovde Glacier in East Antarctica, always thought to be the stable region. This is a concern as this is the first time such a phenomena has been observed on this part of the ice sheet, previously it has occurred in the warmer Antarctic Peninsula and is thought to of resulted in the shattering of the Larsen B ice shelf (2002).

President-Elect Trump...

Although not strictly in keeping with the theme of this blog I feel this next post is important. In just 2 weeks the most highly emitting nation in the world is put under command of a climate change sceptic. Now it’s easy to jump on the bandwagon here regarding Donald Trump, however, I will refrain from doing so. What I will endeavour to achieve is rational; balanced post highlighting the problems the progress against climate change may face.

The Paris Agreement of 2015, brings together all nations under a common cause to “undertake ambitious efforts to combat climate change and adapt to its effects”. A moment of great progress in the face of global necessity. Its central aim is to keep global temperature rise below 2degrees and although extremely optimistic, it does provide a necessary first step in a lot of nations in the conversion of national policy with a wider aim. It requires global best efforts to establish appropriate financial flows, a new technology framework and an enhanced capacity building framework. The framework currently has 122 parties ratified of 197 including the UK, US, China, Russia, and India. In the run up to his election, Donald Trump conclusively stated that he would be pulling out of the agreement under the pretence that he believes climate change is a concoction. In November 2016 this changed, he now has an open mind about the policy. However, we must be well aware of his original intentions especially given his leniency to be manipulated by oil and coal embracing states. Similar to the 24 state demand for Trump to kill the centrepiece to Obama’s internal emission plan, the reduction of carbon emissions to 32% below 2005 level by 2030. It is clear that his turbulent stance on climate change could present significant barricades to successfully implementing low-carbon economies global. At least 630 firms in the US with a collective revenue of almost $1.15trillion have used their economic power in the US to urge Trump to reconsider. Only time will tell if the climate change debate will take a hostile turn despite its recent progress in the coming months.

What we can learn from the last glaciation

The major threat of abrupt climate change comes from a combination of the three systems discussed in this blog. The major tool for initiating glaciation is the Arctic Meridional Overturning Circulation, a part of the Thermohaline system. Henry et al (2016) found that increasing CO2 levels coincided with the H-stadial reductions in AMOC. This warming then caused the discharge of major icebergs from the Greenland Ice Sheet and a melt in sea which kick-started the cooling the disruption of salinity and temperature in the surface waters of the Arctic. Therefore, inhibiting the circulation and causing global cooling. This extreme swing pattern is not a new concept, James Lovelock’s early ‘Gaia hypothesis’ stipulated that the more extreme we force the global system the more extreme the reaction will be in order to eliminate the forcing. In that case either rapid heating to cause total melt or an onset of glaciation, the latter being the more scientifically sound.

Schmittner characterises the whole process as general warming and cooling in the North Atlantic and the opposite in Antarctica. This characterisation is consistent with disruptions to the interhemispheric heat transport of the thermohaline system. As previously mentioned, warming in the Arctic trigger the cooling through melting of ice causing massive freshwater influxes. Recent evidence reinforces this using deep sea sediment ratios. It transpires that when around a 2degree C differential arises between the North Atlantic and the sub-tropical North Atlantic it corresponds with a sever slowing or even collapse of the AMOC.

What is the likelihood of this happening to us?

Using 4 climate scenarios devised by the IPPCC in their 5^th Assessment Report, Cheng et al (2013) assessed the likelihood of the RCP scenarios causing changes within the AMOC. RCP4.5 assumes an emissions peak of 2040, this is the most conservative estimate given the changing tide of consumers in Asia and an unwillingness to cut emissions in the US. Using this scenario by the year 2100 the AMOC will see a projected weakening of 5-40%, this rises to 15-60% in the RCP8.5 scenarios which assumes continuous rise throughout the 21^st Century. Although most likely an extreme case the RCP8.5 scenario shows that a significant weakening of the system is feasible within the 21^st Century which will incite massive regional climate changes a pose new unplanned problems for the world population. The more conservative RCP4.5 shows a stabilising of the AMOC in the latter half of the 21^st century, however a 40% weakening is still significant enough to bring about noticeable shifts in regional climates, so much so it may generate new climate challenges in new locations such as flooding a drought, or exacerbate those already plaguing the global population. 5-40% is a significant ranger considering the consequences however it does provide a confirmation window for Schneider et al (2007) and Cheng et al (2013) who predicted 25-30% weakening by 2100 and 21% (RCP4.5) and 36% (RCP8.5) which are much more precise observations. Furthermore, Cheng et al concluded through multimodel assessment that North Atlantic SST variability in the late-19^th to early-20^th century is consistent with external forcing implementing aerosol forcing as the main driver of AMOC shifts. This is not to say that CO2 may not result in a similar fate as can be seen from this blog alone a number of academics all agree that the forcing is present and a pressing concern the only ambiguity lies in by how much the AMOC will weaken.

Is Geoengineering a Solution? A review of Cvijanovic et al, 2015.

The most likely tipping point and if not at least the most significant positive feedback mechanism in the Arctic system is the albedo feedback of sea ice. This article bypasses the assessment of feasibility and methodology and look at if we could whiten large areas of the Arctic Ocean, could we in fact counter this feedback loop and cause polar cooling.

The study utilises the CSEM global coupled climate model incorporating atmosphere, land, ocean, and sea ice models. The newer CESM model results in better representation of the meridional overturning circulation and sea surface temperature, in comparison to the CCSM3 model.

The method would operate by increasing surface albedo which would result in high latitude surface budget alterations and surface cooling which would spread aloft and southward. This method opposes the geoengineering projects that propose to block incoming radiation with injecting sulphates in to the stratosphere, as this aims to alter the total energy budget via the incoming radiation. Caldeira and Wood, 2008 and Tilmes et al, 2014 modelled these scenarios with reasonable success, although Tilmes concluded that currently the amount of aerosol needed to dim the Arctic is unrealistic and would most likely be blown to lower latitudes anyway so it instead would require extremely large reflects positioned in space above the pole.

The Important Part

The imposition of ocean albedo alterations in the Arctic resulted in the desired recovery of sea ice and decreased warming, with a trend or recovery over the first two decades and no discernible trend beyond. Its success operates with an efficiency peaking at 76% when albedo is enforced over 75-90 degrees North, lower than that proves ineffective in causing ice to recover as it is too far South, 80-90degrees also fails as the coverage of ice is already rather covered therefore little room to alter albedo.

Its success stabilises the ice cover at around 40% of the preindustrial value, which for context, is 37% higher than should nothing be done at all in the case of a 4xC02 climate with about 10degreesC in the Arctic. However, even the most extreme cases of the model have only a modest impact on sea surface temperatures and permafrost.

What this reinforces is that sea ice is a self-supporting system as this one feedback mechanism can cause sea ice to reform and stabilise. It also states that the effects of this reclaiming of sea ice effects the mid-latitudes and the precipitation pattern experienced there.

In essence then, this report serves to highlight that sea ice, although effecting precipitation patterns in the mid-latitudes is actually rather insignificant in terms of its ability to incite a change within the climate system.

Figure 1: "Annual surface air temperature anomalies (K) between 30° and 90°N in modified ocean albedo simulations relative to the control 4xCO2 simulation. Dashed areas indicate the anomalies that are statistically significant at the 95% confidence level. In addition to the Arctic cooling, altered albedo simulations also show notable warming off the West Coast of North America (less pronounced in alb70–80N but still present). This pattern of temperature response is found in all simulations with imposed albedo modifications. Thin and thick contour lines indicate the areas with annual mean sea ice fractions larger than 15% and 80%, respectively." (pg. 5). Credit: Cvijanovic et al 2015

On a Wider Note

The IPCC seems to think geoengineering is vital to restrain global warming, specifically carbon capture, so much so that the U.S. Department of Agriculture guaranteed a loan of $91million to build a carbon capture facility in Louisiana. However, it is most likely not enough to halt global warming. At best projects that block incoming radiation are a plaster that needs regularly refreshing in order to block further degradation while we find a solution to reduce the massive amounts of CO2 filling the atmosphere. CO2 removal from the atmosphere sets a dangerous precedent for producing CO2 I the first place and could just end up playing a continuous game of catch-up. The only real solution is to overhaul the global system and ‘turn the tap off’ instead of trying to widen the plug.

Consequences of a Melting Greenland Ice Sheet

At its extremity a complete melt would cause a global sea level rise of about 6 metres, although this pales in comparison to the 60 metre rise we would be faced with should Antarctica melt, however unlikely. However, we’ll ignore that part and focus on the Greenland Ice Sheet. 54% of Asia’s urban population resides in low-lying coastal areas (Kumar, 2013), according to geohive.com that stands at a population of over 2.1 billion people. This means that in Asia alone over 1 billion people are at risk of rising sea levels.

Figure 1: Visualisation of the cumulative melt days observed on the Greenland Ice Sheet. Credit: NSIDC

Let’s Look at the Melt, and when will it affect us?

Importantly, the rate of melt is increasing. In fact, between 2002 and 2009 the rate of ice loss more than doubled from 137gigatonnes/year to 286 gigatonnes/year. This halves the lifetime of the sheet. Rather obviously though, Greenland strength is the cooling caused by its immense size, as it shrinks it loses its source of cooling therefore melts quicker. Now that our CO2 levels have increased above 400ppm permanently it is expected that the ice sheet will lose 20 to 41% of it volume over the next 400 years (Stone, 2010), equivalent to roughly 1.4-2.8 m sea level rise. Despite the ARR noting that process we’d expect to see over millennia are occurring on a decadal basis the threat from the Greenland Ice sheet is a long-term one. Short-term effects are negligible, and although that can give us comfort we are continually accelerating that melt.

Consequently, we’ve got time. Not to say that should affect the urgency of climate awareness and action but at least in this regard we can start the planet on a path that will halt this melt process.

Consequences of Arctic Sea Ice Melt

Although a perennially ice free Arctic Ocean may be decades away, an ice free summer is a much more pressing reality. Fundamentally, this means the temperature increase is so that it melts all of the seasonal ice annually and consequently starts to erode down the solid multi-year ice. This point will almost undeniably occur within our lifetime and maybe sooner than we think. Basic extrapolation of sea ice volume data places it in roughly 2020. Given, the simplicity of this prediction it would be foolish to take it as truth, however, Overland and Wang (2007, 2009, 2012) used climate model projections as well as encompassing several more severe drops such as 2007 and 2012. Climate models using CMIP5 are often cited as being too conservative (Kumar et al, 2013), yet they still predict a sea ice free summer by around 2040. Considering this is considered a conservative estimate it may well be closer towards the models that assimilate rapid changes which predict around 2030.

2030? Is that our best guess? Holland et al (2006) would agree. Despite it being 11 years later the paper predicts several rapid ice extent retreats, each one 4 times larger than observed decline. Incidentally this would be an underestimate, both the 2007 and 2012 minima were far lower than was predicted (NSIDC), this makes his estimate of 2040 using 7 different climate models arguable conservative.

Figure 1: Sea Ice extent in September 2015. The gold line represents the 1981-2010 average September extent. Credit: NASA

So what if we have ice-free summers by 2030?

Departing from the physical and environmental consequences let’s look at the anthropogenic impacts. By this, I refer to both the Inuit populations whose livelihoods rely on the formation of the sea ice, but also to the market and how this new scenario we have created can be exploited.

Tourism to the region has already increased over the past decades with more of the Arctic ocean becoming more and more accessible to cruise ships for longer times within the summer. Adventure Canada have run tours to the Arctic for 25 years and operate as sustainably as possible, including engaging with locals through employment and meetings to not impose on their culture however a new wave of tourist industries may not carry out the same procedures. Referring back to environmentalism, the burning of diesel produces non-organic black carbon, as opposed to that produced by forest fires which can bring about cooling this form does the opposite. Shipping contributed to 7-9% of global black carbon (http://www.theicct.org/blogs/staff/black-carbon-emissions-shipping-fact-checking-conventional-wisdom) and given that it accounts for 90% of international trade (International Chamber of Shipping, 2014) it is an acceptable level. However, in the Arctic unfortunately the same cannot be said. Localised production of black carbon by increasing levels of cruise ships and oil seeking ships, read on, causes a layer of black to form on top of the remaining ice within the area. Thinking back to the albedo effect, this new dark surface causes increased shortwave radiation absorption directly into the ice, promoting melt.

Despite Shell announcing in September 2015 that it would be abandoning exploration in Alaska for the foreseeable future, it is not likely to last for long, certainly not for the rest of the field. Unfortunately, with dwindling land and ocean supplies of oil the Arctic is the next suspected area for exploration. Despite difficulties faced by Kulluk in 2012, ran aground after losing its tow in the heavy weather, there is almost certainty that companies will move back in the coming summers as it becomes safer and safer to explore during the summer months. This brings with it the dangers of oil spills among other incidents, all of which would be catastrophic in such an environment.

Figure 2: The Kulluk Oil Drill Barge run aground in Northern Canada after it became detached from its tow line in stormy seas. Credit: United States Coastguard

A quick cultural run down.

The loss of Arctic Sea Ice and it's subsequent effects on wildlife habitats, numbers, and migratory behaviour; the transport routes needed to subsist; the duration of seasons; and the condition of fisheries and wild marine life are vital to the survival of native populations. The Arctic Resilience Report released in 2016 states that the mobility of the populations and their animals is already greatly reduced therefore causing a massive change in the ecosystem structure within the polar regions. The increased tourism may also reduce the sense of place felt by natives as well as the effects of a dominant and disruptive body of tourists entering their social system.

Arctic Resilience Report, Briefly.

Newspapers today have embraced the concept of a tipping point almost entirely. Whether that be because ‘slow gradual decline’ doesn’t quite have the same grip as ‘beginning of downward doom spiral’ or whether it be as a result of the Arctic Council. The Independent, The Guardian, The Daily Mail. All major newspapers and all spreading the word that we have passed or are rapidly approaching a tipping point in the Arctic. However, many scientists disagree. It is a contested topic however the Arctic Council seem pretty conclusive in its 2016 Arctic Resilience Report. Being made up of the 8 Arctic nations it provides an academic balance of researchers in addressing 19 of the current threatening 'regime shifts' including that of the Arctic Sea Ice, Thermohaline System and the Greenland Ice Sheet. Conclusively however, they state they exist, and that these regime shifts are not catastrophic. In terms of Arctic Sea Ice, Zhang and Walsh (2006) propose that there are counter-mechanisms that will halt a further regime shift beyond ice-free summers. A note of concern is that the report states that changes in the Greenland Ice Sheet that were thought of as being millennial shifts are occurring on a decadal scale. Due to the size of the sheet no immediate threat is posed, yet we should take note at the severity of the forcing is a result of anthropogenic influence.

The Polar Vortex?

Our understanding of Arctic Sea ice is forever incomplete. The extreme interconnectedness of the global system means that despite decades of research we are forever furthering our understanding. a recent example of this comes courtesy of David Barber, a Canadian scientist. In a TED Talk last year he presented the early basic ideas of the concept, alongside a good overall summary of the problems facing sea ice.  It is only now though that this new concept is of concern, a recent article in Nature Climate Change suggested that this year we could feel the effects of a weakening polar vortex significantly. Previously it has been linked to cooling in the Pacific mid west (2012), however, this Winter as a result of the continual weakening as a result of global warming melt sea ice its effects could be felt across Europe and Asia.

Figure 1: An animation depicting the traditional polar vortex. Credit: Washington Post

A strong polar vortex holds the cold air into the Arctic decreasing the air temperature in the Arctic and allowing for warmer temperatures further South, as visible in Figure 1. The now more unstable vortex is unable to function as it has done previously, as a result we in the UK, as well as North America, Northern Europe and Asia, could experience severe cooling in February. Although this may be inconvenient it isn't the end of the world. This would set a new precedent for the anomalies as previously it has only affected Northern USA.

Figure 2: The adjusted, weaker polar vortex sinking over the USA causing cooling through the US. Credit: Washington Post

The more significant impact can be found in the Arctic. This loss of cooler air will most likely contribute to a warmer surface air temperature in the Arctic. Although this is still a recent topic of inquiry so it is unsure as to how it will effect the Arctic this winter we can predict that it will maintain the seriously low rate of ice formation that has been so prevalent this winter. Due to the lack of research it is unclear how the polar vortex will shift however there is no suggestion of a tipping point instead the vortex has weakened steadily over time, however, the effects have onset rather immediately.

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.

Update on Arctic Sea Ice and a brief introduction to the Thermohaline circulation

Sea Ice Update

November 2016 set a record low for average ice extent. This reflects this years’ unusually high temperatures, winds from the south and a warm ocean. This November’s extent was the lowest on satellite record. The temperature was so warm that for a period in November extent decreases by 50,000km2 per day as opposed to the long-term average of 69,600km2 growth (NSIDC). Ice growth was less extensive in the Kara, Barents, East Greenland and Chukchi seas and larger in the Beaufort and East Siberian as well as Baffin Bay (NSIDC). The exceptional warmth this year could signal a step beyond the tipping point only time will tell. If a similar pattern of ocean and surface warming in the Arctic continues next year, the sea ice as well as the Greenland Ice sheet could experience rapid deterioration, flooding the global climate network with changes.

Continual and current updates can be tracked here: http://nsidc.org/arcticseaicenews/.

Background to the Thermohaline

The thermohaline system is a part of the large-scale ocean circulation that re-distributes heat across the globe. It relies on temperature and salinity as drivers with the Arctic ocean and waters of Antarctica being major areas of sinking. These are supported by warm surface currents such as the Gulf Stream which transfer heat away from the equator in the Atlantic but normally upwell in the Southern Ocean (Rahmstorf, 2003). The major benefit of such an intricate system is the mixing that is allowed transforming the world’s oceans into a single global system. Although its greatest asset, this also means it is its greatest vulnerability. Failings along any point of the system can causes a shutdown of the circulation inducing rapid shifts in regional climates.

Arctic Sea Ice: Summary and Feedbacks

2007 – Average extent, 4.28 million square km. Minima, September 16^th. An unusual atmospheric pattern with high pressures over the Central Arctic Ocean and lower pressures over Siberia caused clear skies in spring and summer, intensifying the melt. However, it is worth noting NSIDC Research Scientist Julienne Stroeve noted that at this point the seasonal ice cover was thinner than usual anyway.

2012 – Average extent, 3.41 million square km of sea ice. Minima, September 13^th. In contrast to 2007 when climate conditions caused the rate of melt, the conditions in this case were much more mild. In fact, 2012 was a stark representation of the declining multi-year ice present in the Arctic Ocean. This means that the seasonal ice becomes the dominant coverage. Although the extent was larger than 2007 in some parts of the central Arctic ocean there was a notable lack of ice in the marginal seas. This is a result of warming sea surface temperatures inhibiting the formation of seasonal ice in these areas.

2016 – Average extent, 2.55 million square km. Minima, September 10^th, increased melt occurring all the way up to this point. Although the ice extent minima in 2016 was higher than that experienced in 2012, as visible in Figure 1, its current trajectory implies that the 2017 maxima will be the lowest on record. Early October daily ice growth was significantly the lowest documented, October 20^th set the new low for daily ice growth. It began to recover towards normal averages later in October however, ice extent continues to be noticeably lower. The NSIDC identified higher sea-surface temperatures as well as unusually high well into the atmosphere limiting the October growth. Lowest October area coverage on satellite record, 400,000km2 less than the previous lowest extent in 2007.

Figure 1: cesm.ucar.edu/models/ccsm4.0/

From the above data and Figure 1, courtesy of the NSIDC, it is clearly evident that sea ice cover is following a decreasing trajectory. In 2012, the NSIDC noted that the seasonal ice cover forming in spring and winter was becoming so thin that it no longer required extreme persistent weather to melt the ice as in 2007. However, the years following returned to a more expected level of cover representing the continual reduction in multi-year ice, as opposed to extreme formation drop. However, 2016 is different. 2015-2016 was the year of El Nino. This means that we should have experienced a disruption in the pattern, yet this never came. The low levels of seasonal ice coverage currently occurring the Arctic ocean will result in rapid ice cover loss come March 2017 and therefore a greater reduction in multi-year ice. It is clear then that this is not a natural occurrence and the impact we, as humans, are having on the planet is driving the climate to unchartered territory. This also provides difficulties when scientists look to predict. The extreme interconnectedness and apposing feedback cycles make determining a conclusive list of consequences is near impossible.

Now, on to the important stuff. The Arctic Sea Ice has long been identified as sensitive to global climate changes. However, more importantly, changes in the Arctic sea ice is amplified throughout the global system. The main feedback mechanism involved within the Arctic ocean is the ice albedo effect. Albedo refers the reflectivity of a surface. The white ice reflects as much as 90% of solar energy (NSIDC) therefore the approximate 60% loss in ice cover in the past decade is a significant loss in reflectivity. The increased energy warms surface temperatures and exaggerates the ice melt. This excess warmth is fed back into the global climate system increasing the global temperature. Evidence of this is provided by Screen and Simmonds (2010). Using ERA-interim they assessed the vertical profile of warming in the Arctic concluding that arctic amplification as a result of sea ice and snow cover is a key feature in the warming since 1989. They also noted that winter and autumn surface temperatures are increasing by 1.6 °C per decade between 1989 and 2008. A trend that if continued could mean the arctic ocean becomes warmer than the freezing temperature of sea water (2°C) during winter, meaning no formation.

The results of this consist of a variety of global impacts. Firstly, and the most direct is the enhanced melting of the Greenland ice sheet and Antarctic sea ice. Subsequently causing a large sea level rise permanently flooding low lying land. A secondary yet possibly extremely significant impact of this reduced ice formation is reduced salinity in the arctic ocean. The arctic ocean plays a vital role in the continuation of the thermohaline circulation however salinity is the driver of the water sink that creates Atlantic deep waters. As water freezes salt is deposited into the remaining water, increasing the salinity and causing it to sink. A slowing of the thermohaline would result in less heat being carried to Arctic waters therefore hindering ice reform. However, it will also hinder the redistribution of heat around the planet. Higher latitudes would become colder and drier with mid-latitudes becoming hotter and wetter. As well as causing more coming extreme weather events. A direct impact of rising sea temperature is the inhibiting the role of oceans as a CO2 sink. As the temperature of the water increases its ability to absorb CO2 decreases. Due to the interconnectedness of the global climate system it is easy to get carried away when discussing the impacts so I have limited the depth of the impact discussion.

The question is then; can we change our trajectory? Without the immediate cooling of our oceans, this feedback will continue to enhance. And with the Paris 2015 conference aiming to limit global temperature rise by 2°C this immediate change will come. It is therefore difficult to see is reverse this trend within the foreseeable future.