Time to change or expect a seven metre sea rise

Story & image Mary Gardner

Each of us is an individual world maintained within a larger collective world. For our average 72.6 years, our human bodies maintain a temperature between 36.5–37.5°C. We can’t tolerate external heat over 35°C with more than 50 per cent humidity. The living coral polyps of the Florida Keys are reported to be 4,000 years old, all the while relying on the seawater around them staying within 23–29°C. But what of the age and range of temperature tolerance for an entity such as the Inland Ice of Greenland?

Some four billion years ago the basement rocks of Greenland were laid down. Fast track forward two million years, when the present inland ice developed. The current island is 2,166,086 square kilometres. But 81 per cent is covered by ice, the weight of which deformed the central rocks and created a basin. This cup holds so much ice which, when melted, would raise the global sea level by seven metres.

Melt season is underway

From April, on the Danish website Polar Portal, researchers will report the annual monitoring of the ice melt. A melt season is under-way on the third consecutive day that more than five per cent of the surface ice starts melting. In 2019, that melt started on 30 April, about a month earlier than 2018 and the second earliest time since 1980.

The quantity and variety of changes in ice is stupendous. In 2019, surface melt occurred over 58 per cent of the ice cap. The loss of glaciers due to icebergs calving off from them was 491 gigatonnes (Gt). (A Gt is one billion tonnes or a cubic kilometre of ice). That’s more than the total losses from 1981 to 2010.

Warmer waters means greater global heating

Accelerating the 2019 ice melt was the loss of sea ice. Throughout the Arctic Sea, the abundance of sea ice was at the lowest since records began 40 years ago. Darker waters absorb more heat, warming more quickly and staying warmer for longer.

Instead of a vast white slush and ice, reflecting the sunshine away from earth, the warmer seawater hastens three different ice changes. More sea ice is melted. More surface ice melts. Finally, the warmth melt the sea edges of the glaciers around Greenland, resulting in more icebergs.

The twist in this tale is that the inland ice has been keeping a diary for over 100,000 years. Each year, another layer upon layer of snow compacted into ice holding small bubbles of air. In 1955, 1963–66 and again in 1992–93 research teams laboured to collect six core samples. They had to drill through the ice to the rock three kilometres below. The last two attempts finally recovered cores of that entire length.

The cores are stored in dedicated freezers. Although the cores were taken at sites across the entire ice cap, the rings are clear, easy to count and most importantly, correlate with each other. They also correlate with global geographical and historical events such as volcanic eruptions and changes in climate.

The story ice cores tell

In the 2019 book The Ice At The End Of The World, author Jon Gertner speaks with Joan Fitzpatrick. She is the curator of some ice cores which are stored in dedicated freezers in Denver, Colorado. She shows him Core 1678, a metre long, dated 11,700 years ago. She points out one end where the few wide bands of ice signify an Ice Age. The thin bands at the other end suggest the Ice Age no longer existed.

Researchers Taylor and Alley investigated the stable oxygen isotopes in this particular core sample. They finally concluded that the climate changed by 7.7°C. But their most shocking result was that the transition was abrupt. From the tipping point and into the new climate regime was only ten years.

From the diary of the inland ice can also be read the temperatures of the past. Of special interest is the temperature of the last 12,500 years, our Holocene era. Even more telling is that of the last 2,500 years.

In 2009, Vinther and his team graphed all these temperatures calculated from ice cores at intervals of twenty years. They extended the chart with the observed temperatures from 1880–2018. Then they added two projections of temperature changes out until 2100: 3°C and 5 °C above pre-industrial average temperatures. The first is a world where emissions are drastically curbed and the second is where they are not.

Seven metre sea level rise?

The result suggests by 2040, a few °C increase for Greenland’s ice will make a powerful difference. Temperatures never known over the past 12,500 years will mean its ice will become part of that seven metre sea level rise.

As a result of the global warming already started, the Greenland ice melts of 2019 already exceed these projections made in 2009. Even as we barely understand age and temperature tolerances of this ice, we are watching it disappear. The same is true of the sea ice of the neighbouring Arctic Sea.

Closer to us in Eastern Australia, we reach mid March 2020 with continued heat stress for corals. By 25 March, Professor Terry Hughes offers a preliminary report of his aerial survey of the Great Barrier Reef. Speaking to the Guardian, he describes a severe bleaching event. Many of these corals have barely recovered from serious events in 2016 and 2017.

After the heat of summer, all the fire and flood, we are now in a viral pandemic and carefully monitoring our own selves. Us, the corals and ice: all sensitive and none immune to the changes of our collective world.