• Mechanical break-up. Powerful winds shatter the ice cover, setting floes in motion so they drift and collide.
• Delayed refreezing. In deep winter, newly opened gaps in the ice would normally freeze over within days. A following storm keeps conditions turbulent and slows that recovery.
• Compaction in summer. Storms are weaker in the warm season, but winds can still push floes northward into other ice, reducing the total area covered.
• Attack by heat. Cyclones carry warm air that melts ice from above, and they stir up relatively warm seawater from deeper layers toward the surface.

The regional impact varies enormously. In some areas, clustering increases the effect on sea ice by 1.5 times; in others, the effect becomes as much as seven times stronger.

"On average across the entire Arctic, cyclone clusters reduce Arctic sea ice cover by about twice as much as conventional, isolated low-pressure systems. This condition also lasts about two and a half times longer," says Aue.

The key, the researchers found, is that repeated storms prevent the ice from recovering between disturbances, so the damage accumulates. The overall effect matters more than the strength of any single storm.

Could warming make it worse?

The long-term trend is troubling. Sea ice loss linked to cyclone clusters has risen substantially over recent decades, according to the analysis.

One likely reason: the ice itself is changing. As global temperatures rise, Arctic sea ice becomes thinner and more mobile, and less able to withstand the forces cyclones generate. During summer, an increasingly warm Arctic Ocean could amplify the effect.

Aue warns of a possible downward spiral: "We could be entering a self-enforcing feedback loop: the weaker the sea ice becomes, the more cyclone clusters can reduce its extent, which in turn weakens the sea ice."

That conclusion remains preliminary in one respect. The team is now using climate projections to test whether the intensification seen in recent decades will continue in the future.

Why does this matter beyond the ice?

Sea ice acts as a natural barrier protecting Arctic coastlines from powerful waves. As that cover retreats, coastal communities face greater exposure to severe storms. Rising permafrost thaw is weakening the same coastlines, making erosion and storm damage more likely.

Accurately representing cyclone clustering in models could therefore improve projections of both future ice conditions and coastal risks.

"Until now, there has been no systematic analysis of the impacts of cyclone clusters in the Arctic. With our work, we are filling a knowledge gap and lay an important foundation for projections that can depict the future of the Arctic sea ice — a central component of the global climate system — as accurate as possible," Aue said.

The study, authored by Lars Aue, Sofie Tiedeck, Peter Finocchio, Timo Vihma, Petteri Uotila, Gunnar Spreen and Annette Rinke, appears in Nature Communications.