Each January many of us think about what old habits we can let go of and what new things can we bring into our world. Arctic scientists think about things in a different way: how can we hang on to the old and better understand the new?

We’re talking about sea ice, of course, rather than our smoking or drinking habits (well, sometimes we think about those too). The old ice in our world is of critical importance. Global society can’t maintain or protect the things we hold dear without it.

What do we mean? And why should you care?

Simply put, old ice is multi-year ice. It has been around in the Arctic Ocean for more than one year.

But the area of old ice is shrinking dramatically, and unless we reduce our emissions we are pretty much guaranteed to lose it all. An Arctic without sea ice is like your house without its roof. But in this case the house is very large; it covers the top of our world.

Multi-year ice is a key part of the Arctic system because it is thicker and stronger than younger ice. It not only controls the dynamics of all the rest of the ice in the Arctic, it also influences the Arctic ecosystem by limiting the amount of light entering the water column. Changing the distribution of light disrupts the breeding cycle of marine organisms such as phytoplankton and puts tremendous pressure on the regional food web, including fisheries.

Like anything old and grisly, multi-year ice used to be able to survive the summer melt. But the summers are getting warmer. The Arctic is warming more than twice as fast as the global average (known as Arctic amplification), and the old ice is melting. It is being replaced by younger ice (formed in the winter), which - being thinner - cannot survive the summer melt. The ongoing loss of multi-year ice is a key factor behind Arctic amplification. When the Arctic Ocean is covered in ice, 80% of the sunlight gets reflected back to space, but with open water, the ocean absorbs 80% of the sunlight.

The less multi-year ice there is, the less the Arctic is able to regulate the global climate by reflecting sunlight back into space. Without ice, or with very thin ice, the Arctic Ocean instead absorbs the sun’s heat, which inhibits ice formation the following winter - and the downward spiral continues. At the end of the winter the ice is thinner and more susceptible to melting, hence the massive retreats we are seeing.

So a good indicator of the resilience of the global climate system is to assess how much multi-year ice is left.

The trouble is, it’s disappearing fast. The Arctic is in crisis.

 The scale of Arctic ice loss is at crisis point
The scale of Arctic ice loss is at crisis point
Image: Arctic Basecamp

Without sea ice in summer, we lose much of the Arctic’s protective ability to reflect sunlight away from Earth. This could dramatically accelerate global climate change and the risks of impacts that can affect food and water security elsewhere, as well as increase rising sea levels and extreme weather events. We know that in 2018 alone, extreme weather events cost US$320 billion. We also know that the frequency and impact of extreme events increases as the world warms. In fact, research is revealing that many extreme events are indeed related to changes in the Arctic. So when global experts identify extreme weather as the number 1 global risk, they are implicitly talking about the dangers of Arctic change.

Why is the Arctic sea ice declining so significantly? Research shows a strong and direct correlation with CO2 emissions. In fact, for every metric ton of CO2 we add to the atmosphere, we lose another three square meters of sea ice. While this may not sound like a lot, it starts to add up. To put this into context, we can relate country level emissions. Countries like the US, Canada, Australia and Saudi Arabia are some of the largest contributors to sea ice loss per capita, with Qatar topping the list.

 Which countries' populations are responsible for the most summer sea ice loss?
Which countries' populations are responsible for the most summer sea ice loss?
Image: Stroeve & Notz (2018)

Converting emissions from the top 4 emitters into Arctic sea ice loss for the year 2017:

USA: 5.3 Gt CO2 = 16,000 km2 sea ice loss (more than 90 times the size of Washington, D.C.)

The EU: 3.5 Gt CO2 = 10,500 km2 sea ice loss (100 times the size of Paris)

China: 10.0 Gt CO2 = 30,000 km2 sea ice loss (more than 10 times the size of Hong Kong or approximately the size of Belgium)

India: 2.5 Gt CO2 = 7,500 km2 sea ice loss (five times the size of Delhi)

As we now know, global emissions have continued to rise. The latest estimates from the Global Carbon Budget for 2018 show a global annual increase of over 2%. This will have physical consequences for Arctic ice.

Let’s take a closer look at the 2018 numbers. Last year, the world produced a total of 37.1 gigatonnes (Gt) of fossil-origin CO2 emissions. When converted to sea ice loss this equates to 111,000 km2, almost three times the size of Switzerland. Based on 2018 emissions by country, China’s contribution increased by 4.7%, the US’ by 2.5%, the EU’s declined by -0.7% and India’s increased by 6.3%.

We can also look at our responsibilities in another way. Take coal as an illustrative example. Blackrock, the world’s largest investor, holds 400 million tonnes of thermal coal. While the carbon content of coal differs quite widely, we can assume an average carbon content of 70 % for Blackrock's coal. That is roughly 1 Gt of CO2. This amounts to 3000 km² sea-ice loss equivalent. This translates into a loss of ice roughly the size of Shanghai in one year - that is, 6,340 km2.

The Arctic is the poster child for the importance of the +1.5C target agreed at the 2015 UN Climate Conference in Paris (COP21). Simply put, if the world can maintain a ceiling of a +1.5C warmer world we can save the Arctic summer sea ice, and likely prevent some of the most serious climate impacts around the world. But once global temperatures go beyond this limit we will probably lose the summer ice, triggering serious consequences for our economies and societies worldwide, including increases in extreme weather in the mid-latitudes.

People often ask scientists when will the Arctic ice disappear. It’s not a matter of time, however, but rather how much more CO2 we put into the atmosphere. Just 800 Gt more of CO2, and it’s gone. At current rates of annual emissions of 35 to 40 Gt per year, the window of tim we have to preserve the Arctic summer sea ice is closing very rapidly.

At the 2018 climate conference - COP24 - Christiana Figueres, a former Executive Secretary of the UN Framework Convention on Climate Change, and over 100 co-authors and co-signatories outlined a detailed plan on what needs to happen next. Ramping up ambitions under the Paris Agreement is the only way forward. From an Arctic sea-ice perspective, the Paris Agreement means the difference between having sea ice or not.

Luckily, all this makes good financial sense. Economic studies suggest that the “acceleration of climate change driven by thawing Arctic permafrost and melting sea ice could cause up to $130 trillion of extra economic losses globally under the current business-as-usual trajectory over the next three centuries. If global warming is limited to 1.5C, the additional cost will be reduced to under $10 trillion.”

Arctic summer sea ice has been around for at least thousands of years, if not longer. It may be soon gone, unless we start to bend the CO2 emissions curve soon. Arctic scientists can bring the facts and robust projections on Arctic change and global risks. Solutions must come from politics, business and civil society.

The authors of this article will be setting up an Arctic Basecamp at Davos 2019. Find out more here.