The Severe Historic Melting of Arctic Sea Ice

The extent of Arctic sea ice at the end of summer has reduced by around 40% since satellite records began in 1979. Meanwhile, the average thickness has more than halved. The loss of Arctic sea ice could have severe implications for the global climate, affecting the jet stream and perhaps causing more frequent extreme weather events.  

The Arctic is warming four times faster than the global average, meaning climate change is already having an impact on indigenous people in the Arctic. While in Cambridge Bay, Canada, I heard fascinating but disturbing stories of how things have changed for them; two in particular stood out. One man told us of astounding changes in snowfall; thirty years ago during winter, the snowfall was so deep that after a storm they would be snowed in to the roofs of their houses. Now, they struggle to travel in some areas because the snow cover is too thin for them to cross safely. Similarly, people spoke of how the thinner ice is already affecting the migration of caribou, a vital food source for those living in the remote territory of Nunavut. These stories not only motivated me in my work, but also gave me an acute understanding of what climate change could mean for the rest of the world very soon.

An Ice-Free Arctic Regardless of Emissions Reductions?

When global warming was first identified, its effects could have been minimized by cutting our emissions. Because of human inaction, it has also become necessary to remove greenhouse gases from the atmosphere and this has been widely accepted. However, we have now reached a more worrisome and much lesser-known tipping point; decarbonisation, while essential, is now insufficient. Even the most optimistic emissions pathway, SSP1-1.9, from the International Panel on Climate Change, beginning in 2015, predicted that we would overshoot 1.5℃ of warming and this has already occurred. Headlines such as “World’s first year-long breach of key 1.5C warming limit” are a clear sign that we are not acting and have little time left to save our planet.

The realisation that decarbonisation is essential but insufficient led me to the field of climate repair and specifically to the dire situation in the Arctic. Sea ice acts as an excellent reflector of solar radiation in the summer, helping to cool the planet; its loss could have devastating effects. While the fact that the Arctic is melting is widely known, the severity of the situation has yet to be fully grasped. Research published at the beginning of March 2024 predicts that ‘‘the earliest ice-free conditions […] could occur in 2020–2030s under all emission trajectories and are likely to occur by 2050’’. Given that an ice-free Arctic is likely, regardless of emissions reductions, it follows that we must consider additional action to restore the Arctic sea ice for the sake of the climate system and also the local populations and wildlife.

Methods for Restoring Arctic Sea Ice

The focus of my research is whether it is possible to restore sea ice by thickening it in the Arctic winter. Sea ice grows naturally on the underside of existing ice, due to the cooling that is provided by the atmosphere above. However, as the sea ice grows thicker it becomes increasingly insulating, thereby slowing the rate of growth. Any snow that falls on the sea ice is an even better insulator and so slows the growth rate further. The idea is therefore to increase the speed at which sea ice grows, by either bypassing or reducing the insulation between the ocean and the atmosphere.

One technique is to pump seawater through the sea ice onto its surface, exposing it to the cold atmosphere directly where it should freeze more quickly, thereby thickening the sea ice. Calculations indicate that pumping 1 meter of seawater could increase the thickness of sea ice by 70 cm (due to reduced natural freezing), thus significantly increasing its chances of surviving melting during the summer. An alternative technique is to pump seawater into snow thereby consolidating it into ice. Removing the air-filled voids in snow reduces its insulating effect and hence increases the rate of natural freezing on the underside of the sea ice. Modelling for this technique suggests that flooding snow with 20 cm of seawater could add 50 cm of ice thickness by the end of winter.

Both of the above methods for restoring sea ice may be needed together to prevent the Arctic from becoming ice-free. Currently, we do not know their effectiveness, making urgent research all the more important. There are many unknowns, such as the behaviour of the saltier ice arising from pumping seawater; the thickness increase that can be achieved; the behaviour of the new ice during summer melting, and the impact on local communities and wildlife. Scaling up to potentially millions of pumps will also be a huge, though not insurmountable, engineering challenge.

Field Trip to Cambridge Bay, Canada

In January 2024, I had the privilege of joining a sea-ice-restoration field test, organised by Real Ice. The purpose of our trip was to investigate the feasibility of pumping seawater to consolidate snow for enhanced natural freezing. In addition, we also engaged with the local, indigenous community to understand their opinions on sea ice thickening. We had expected scepticism from the local people, but the discussions were more positive than I had hoped for. The people we spoke to were enthusiastic that we wanted to do something to protect their ice, and while they had many questions about how they and the local wildlife might be affected, it was clear they could also see potential benefits. Protecting the migration routes of caribou or their own travel routes across the ice—both of which are thinning rapidly—is as important to them as the global climate impact of restoring the Arctic ice.

The experimental side of our trip to Cambridge Bay was also a success. With the help of local guides, we went out onto the sea ice, drilled holes through it and then pumped water onto the surface. The seawater flooded the snow and we were able to make useful observations of the behaviour of the flow and the resulting ice thickness. Of course, there were challenges: temperatures on one day reached nearly –50℃ with the wind chill, preventing us from going out onto the ice. However, overall, things ran as smoothly as can be expected in the harsh Arctic environment. To know whether our snow consolidation successfully enhanced natural freezing requires constant monitoring of the sea ice thickness in our test location and a control site. But we now have the support of local people, who are measuring the ice thickness for us, now that we have returned home. Although I am optimistic, it is too early to say how successful our experiment was and more data will be needed to confirm the results.

Final Thoughts

Decarbonisation is essential, but likely insufficient, to prevent some of the worst effects of global warming. Therefore, we need local solutions to protect vulnerable ecological and climate systems. Some people argue that climate repair could be used as an excuse not to reduce emissions and that doing so would be enough. However, climate repair is not an alternative. Those of us advocating for research into its potential believe it is now necessary together with rapid decarbonisation. Too much time has already been wasted. We must decide now to save the future of the planet by rapidly reducing emissions, removing greenhouse gases from the atmosphere and protecting vulnerable systems.