The Arctic: Heatwaves and habitat destruction

At present there are only 4 million people living in the Arctic, but this number is predicted to rise throughout the twenty-first century as more ice melts on land and in the Arctic Ocean. 

Why is the Arctic so important? 

Sea ice and a deep blanket of snow in the Arctic both act to moderate the Earth’s climate. These surfaces are white and very bright, resulting in a high albedo. Roughly 80% of the sunlight that strikes sea ice is reflected back to space. In contrast dark surfaces, such as the ocean, absorb up to 90% of incoming solar radiation. Albedo is an important mechanism for the planet to maintain climatic equilibrium. In June 2020 Arctic sea ice – and therefore the Arctic albedo – was at its second lowest extent on record with roughly 1,940,000 km² less sea ice than the mean decadal amount for the 1980s (Zach Labe, atmospheric climate scientist).  

Glaciers are also melting in the Arctic Circle. Glaciers that end in the ocean are called tidewater glaciers which, due to increasingly warmer saline water contact, literally ‘unzip’ causing large pieces of ice to fracture, separate or ‘calve’ forming icebergs. The rate of Arctic glacier melt is therefore steadily increasing as the glacial equilibrium tips away from accumulation towards ablation. Arctic glaciers are therefore retreating up their coastal valleys, as the balance between the amount of input versus the amount of output is switching to a sustained negative balance. This is having a particularly severe effect on Greenland which has 79% of its surface covered by ice sheets – the second largest body of ice in the world. 

In general, the bigger the glacier the longer the lag for response. However, the key to Arctic glacial survival is the ice shelf. If the ice shelf disappears a greater flux of glacial ice is released into the ocean, resulting in extensive collapse of the ice sheet behind. Atmospheric change and more marine water have both caused glacial disintegration and a rapid loss of ice shelves around the world. Essentially tidewater glaciers are being melted from the top-down and bottom-up. As ice shelves start to fragment, they are also thin, and the grounding line retreats in a landward direction. The grounding line is the point at which a tidewater glacier starts to float. The retreat of such a line is significant because it can dramatically accelerate the demise of the glacier.  

In July 2019, lead-author David Sutherland published research on the LeConte glacier in Alaska, identifying tidewater glaciers as melting 100 times faster than previously thought when compared to valley glaciers (National Geographic). This is largely from ‘plumes’ of more buoyant freshwater surface melt entering the fjord close to the glacier face, which it then undercuts and erodes. While Alaska has only 50 tidewater glaciers out of a total of 100,000 Greenland has around 200 outlet glaciers which are susceptible to the same dangers. 

What is the jet stream?  

Jet streams are fast flowing currents of air in the atmosphere with wind speeds of up to 200 miles per hour. They are often described as ‘ribbons’ because jet streams can be hundreds of miles wide. The main jet streams are the Polar Front jets and the Subtropical jets – both found in the northern and southern hemisphere. Changes to the Polar Front jets have created the 2020 Arctic heatwave. The Arctic Polar Front jet is a type of thermal wind which normally rises due to the strong temperature contrast in the mid-latitudes. 

Theoretically, in the northern hemisphere high-pressure warm air would move northwards towards the cold low-pressure polar air – this process is called the Pressure Gradient Force. However, the Earth’s Coriolis Effect from the Earth’s rotation causes air to move to the right (in the northern hemisphere) in the direction of motion. 

The Arctic Polar Front jet tends to be further south in the winter since the northern hemisphere tilts away from the sun. In 2020 this natural pattern was severely altered with the jet stream retreating northwards. 

An excellent summary and definition of the jet streams can be found on the Met Office YouTube channel. 

The heatwave 

The Arctic is a meteorologically varied area as it experiences alternating warm and cold air bringing high and low pressure. Below is a diagram by Professor John Wallace, explaining the Arctic Oscillation of pressure when compared with the northern mid-latitudes. It is an opposing pattern: if the Arctic experiences high pressure – it is low in the northern mid-latitudes of North America and Europe, described as the negative phase. This pattern reverses in the positive phase of the oscillation. In 2020 the Arctic became ‘stuck’ in a positive phase creating a stable period of unusually warm weather, like a heatwave.  

The positive phase of Arctic Oscillation has brought storms across the Atlantic Ocean and wet weather to places like Scotland, Alaska and Scandinavia. This movement and the unusually high temperatures in the Arctic are due to the ring of strong winds circulating around the North Pole acting to confine colder air to the upper polar region. Low pressure within the Arctic Circle has pulled warmer air northwards from the lower latitudes. This is otherwise described as a ‘northward swing of the jet stream’ which allows warmer air into the region, raising surface temperatures. 

This positive pattern dominated in the 1980s and 1990s but since 1997 it has fluctuated, switching between positive and negative phases repeatedly. Despite the seesaw nature of Arctic Oscillation, the general trend has been of continued warming with a spike of both very warm and very dry weather across Siberia this year.