An impossibility by which the answer lies in one of our most important heat exchanges of this planet is the AMOC – The Atlantic Meridional Overturning Cycle. This system is a vessel for the transfer of heat between the ocean and the atmosphere. But it is slowing down. Direct measurements of the modern AMOC flow rates show a decline in its strength in the past decade. Due to its relatively ambiguous nature, scientists are unsure of the previous strength flow cycles of the AMOC but know that its decline has previously caused an ice age. It is now described to be in a “subdued” state.
Using high resolution climate models, a team of scientists have found that measuring anomalous temperature patterns on the sea’s surface mirrors the strength of the AMOC in the last century. They’re findings provided the food of the brainchild inspiring the imagination of apocalyptic “cool down” scenarios. The weakening of the AMOC leads to the cooling of the cyclonic system of wind-driven ocean currents that lies south of Iceland – a cold weather system – a very cold weather system.
However, this potential catastrophe does not end here. Authors of the analysis of this bipolar cooling and warming pattern of the AMOC performed climate simulations on the AMOC. Under a 1 percent yearly increase in carbon dioxide, this model mirrored anomalies found in heat fingerprints in the North Atlantic – AMOC slowing. Naturally, the inference became that as a response to anthropogenic greenhouse gas emissions, the AMOC was slowing.
By adding more constraints to their work using sediment trackers, two groups of scientists found the AMOC to be of stable strength from 400AD to 1850 but then weakened near the start of the industrial era. However, between these two groups there was a 100-year difference in their readings. One group claimed that it was our industrial era that spurred the melting of ice age glaciers and therefore causing a high intensity input of freshwater to the AMOC, decreasing its strength by 15 percent. The other group proposed that it was the end of the “Little Ice Age” that spurred this freshwater influx. Of course, 100 years in merely a mayflies’ life in geological time. But who should we believe?
Should we be feeding into our belief of sci-fi action thrillers where we are inevitably our own demise – marching ourselves into an ice age as the AMOC slows to marvel at our celebration of our treacherous creations? Or should we assume that we are simply too ignorant of our climate cycles to propose for even one second that we have any affect on them? After all, our sentience has led to dangerous over-simplifications before.
Luckily there is a way to differentiate between the two groups of scientists. They are both prime examples of the “bottom up” and the “top down” experimental approaches. The first group, proposing that our industrial revolutions are the cause of this circulation slowing, have used the top down approach, their inferences of changes in the AMOC made from reconstruction models spurred experimental evidence to justify this claim. Although, the authors do attempt to subdue doubts by giving evidence of the Icelandic cyclonic system cooling. The second group however, taking a more consequentialist approach, using data from deep water current strength to measure the AMO more directly. However, their evidence was localised and was highly susceptible to local nonlinear effects such as abrupt shifts in current position. Their measurements of the heat content of the Icelandic cyclonic system save this group once more, bridging their localised evidence to broader scale AMOC changes.
How can we interpret the intersection between these two groups? It is accepted of course that the AMOC is slowing due to an increased input of freshwater and has become weak around the time of the great industrial revolution. This weakening, affecting cyclonic systems and North Atlantic heat flows, would cause considerable changes in climate precipitation patterns in the northern hemisphere. Not exactly an apocalyptic scene, but more of an agricultural challenge.
What if the AMOC were the collapse?
With a slowing down with no evidence of decrease of negative acceleration, there is a possibility of AMOC collapse in response to continued melting of the Greenland ice sheet. Imagine the impossibility of this occurring. And then get rid of that imagination. There is actually a 15 percent chance of the AMOC temporarily shutting down in the next 100 years, with most models predicting a likely shutdown in 2300. Especially following the predictions of the Intergovernmental Panel for Climate Change predicting a four degree rise in temperature by 2100. This potentially leading to accelerated melting of ice sheets in the northern hemisphere, a positive reinforcement cycle. The more ice sheets melt, the decreased area of reflective surface in the north, causing increased insolation and therefore more melting. Despite a 15 percent probability, this number does not correlate with the impacts this would have. By scientists, the passing of an AMOC tipping point would be so huge that it is viewed as a low probability high impact scenario.
What has this got to do with an ice age?
Any temperature oscillations always have to do with dramatic climate changes. The slowing or tipping of the AMOC will lead to a huge net cooling of regions such as Western Europe. This may cause longer winters, and increased precipitation patterns. Lakes may freeze over, there may finally be more snow in Scotland and Britain would become even more wet and the Mediterranean would become even more dry during summer. Other impacts would include major shifts in rainfall patterns, increase in winter storms over Europe and sea level rise of around 50cm in the north Atlantic basin. This bulging around this area of the earth is due to gravitational anomalies as well as the earth bulging as it rotates. Of course, the impacts of agriculture, wildlife, transport anergy demand and coastal infrastructure would be highly complex but it is clear that there would be major socioeconomic consequences. This is nothing compared to the catastrophe expected. Although there is evidence to suggest that fluctuations in the AMOC in the past have led to the onset of the last ice age, we will not be dragged into a “The Day After Tomorrow” scenario.
Luckily for us, we do not live at the bottom of the Atlantic and feed on algae and therefore our adaptation is likely to be successful compared to that of marine life. Before this climate tantrum therefore, we should currently be focusing on mitigation. Following IPCC guidelines and urging our European governments to effectively invent, reorganise and develop effective strategies to achieve our Sustainable Development goals to decrease the acceleration of anthropogenic warming. This way we can slow the onset of this AMOC collapse, preserving our wildlife and climate systems.
Written by Lilly Horvath-Makkos
Media by Ben Hyland
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