Natural Climate Variability and The Arctic Oscillation

Last week, I posted about the Larsen B ice shelf, proposing that its break up may have been human induced. There is a lot of uncertainty about climate change at the moment. In my very first post, I highlighted this issue explaining that it can leave you feeling confused about what is actually happening! Some researchers believe that the Larsen B ice shelf collapsed because of greenhouse gases, while other researchers, primarily climate change sceptics, believe that natural climate variability is actually contributing to the climate in Antarctica. This post is going to present their arguments. 

The Arctic Oscillation

Antarctica experiences changes in climate due to natural climate variability. One example of this is the Arctic Oscillation. The Arctic Oscillation fluctuates between a positive and a negative state, as shown in Figure 1. When in a positive state, the Arctic experiences unusually low atmospheric pressure and a warmer climate (Bjornaes and Pal, 2012, 'The State of the Poles', p.19). Furthermore, the jet stream blows strongly from west to east. When in a negative state, the Arctic experiences high pressure and the jet stream is weaker. 

Figure 1. Arctic Oscillation. Adapted from Bjornaes and Pal (2012, 'The State Of The Poles': p.19). 

The Arctic Oscillation affects the climate in Antarctica. A study by Chylek et al. (2010) investigated the effect of the Arctic Oscillation on the Antarctic climate and found that when the Arctic warms, Antarctica cools and vice versa. Additionally, Brunier and Brook (2001) observed this “bipolar see-saw pattern” from ice core records dating back to the last glacial period, demonstrating that this phenomenon is independent of human impacts. Figure 2 is a graph that illustrates the bipolar see-saw pattern, plotting temperatures against time. It is evident that as temperatures in the Arctic fall, in Antarctica they rise, despite emissions and other anthropogenic interferences with climate change.

Figure 2. Bipolar Seasaw Pattern. Source: Chylek et al. (2010).

Arctic (blue) and Antarctic (red) temperature time series smoothed by a 11 year running average (thin lines) or 17 year running average (thick lines)

Larsen B 

The bottom right of figure 1 shows a time series of the patterns of negative and positive oscillation indexes. The circled year represents the year 2002, the same year that the Larsen B ice shelf collapsed. The figure shows that the Arctic Oscillation Index (a measure of the magnitude of the Arctic Oscillation phenomenon) was negative that year, demonstrating that when the Arctic cooled, Antarctica warmed. It can be argued that this warming accelerated the melting of ice during the summer months which led to the break-down of the Larsen B ice shelf. In fact, Domack et al. (2005) conducted a study to determine the stability of the Larsen B ice shelf during the Holocene and found that the ice shelf had been thinning throughout the Holocene, i.e. throughout the past 11,500 years! This is evidence against human induced warming affecting the Antarctic right? 

How does the Arctic Oscillation work? 

In this description, I will explain how the oscillation leads to a warmer Arctic. A similar mechanism operates in the opposite direction to explain Antarctic warming as well. Described by Chylek et al.(2010), winds over the Southern Ocean are drawn to the surface by wind stress. This water is heated by the sun and the Atlantic surface current transports it away from Antarctica. As the water warms more, it travels towards the Arctic leaving Antarctica deficient in heat. The more efficient this transport, the greater the warming. This demonstrates the importance of the role of ocean currents in natural climate variability.

Conclusions

Arctic Oscillation and the work done by the researchers mentioned above are just one of many scientific models and explanations for the Larsen B ice shelf collapse and for climate in Antarctica. If studying Economics and geography at UCL has taught me anything, its that the world is full of uncertainties. Researchers aiming to devise what is human induced and what isn't in our planet will always end up with different explanations because Earth is complex. 

My personal view regarding this matter is that natural causes are not strong enough to determine what caused the Larsen B ice shelf to disintegrate. Although evidence presented suggests that Arctic Oscillation impacts the climate in Antarctica, uncertainty lies in the magnitude of the positive feedback systems between Antarctic waters and heating from the sun. There is also uncertainty in the strength of the transportation of these waters. To me, it seems unlikely that early humans at the start of the Holocene caused enough warming to contribute to the thinning of the Larsen B ice shelf, as illustrated by figure 3 in my post last week. 

That's all today! The score so far is 1-1. Next time, I will explore how tourism has affected Antarctica, thank you for reading!