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.