A research team from the Northwest Institute of Eco-Environment and Resources (NIEER) of the Chinese Academy of Sciences (CAS), together with collaborators from Beijing Normal University and the University of Chinese Academy of Sciences, found that summer rainfall in the Arctic would increase by about 17% under 2 °C global warming, approximately 16% of which is attributed to sea ice retreat. 

Their findings were published in Geophysical Research Letters. 

As global warming continues to intensify, the Arctic, one of the most affected regions, is warming at a rate more than four times the global average. Arctic sea ice, one of the 16 global climate "tipping points", is experiencing rapid retreat. 

Melting ice sea weakens the "white cold cap" effect that reflects solar radiation and exposes a darker sea surface with a stronger heat absorption capacity. This pushes the Arctic water cycle pattern to shift from "snow-dominated" to "rain-dominated". This change significantly impacts the retreat of Arctic glaciers, the melting of permafrost, runoff processes and ecosystem balance, creating a domino effect on global sea level rise and extreme climate events.

To quantify the contribution of sea-ice loss to these shifts, the researchers innovatively combined the large-sample ensemble simulations from the Polar Amplification Model Intercomparison Project (PAMIP) and the Coupled Model Intercomparison Project (CMIP). By separating the climate's response to "total forcing" from that due solely to sea ice retreat, they were able to precisely attribute its impact on Arctic land precipitation.

"Liquid precipitation will further accelerate the sea ice retreat, forcing animals such as polar bears and reindeer that rely on sea ice and snow for food or shelter to face survival crises," said YANG Jiao, first author of the study. It also alters the thermal conditions of the soil, intensifies permafrost thawing and subsequently releases greenhouse gases, creating another feedback loop that drives global warming.

The researchers also found that sea ice retreat contributes more than 30% to increased rainfall in the Arctic coasts of Siberia and North America, forming two distinct rainfall enhancement belts.

Nearly 70% of the increased rainfall is caused by the warming effect resulting from melting sea ice, meaning higher temperatures turn what would have been snowfall into rainfall. The remaining 30% is due to evaporation over open water areas, which increases the amount of water vapor in the air, thereby increasing total precipitation.

"This study not only deepens our understanding of the warming and humidification processes in the Arctic, but also establishes a quantitative relationship model of 'sea ice-precipitation', providing a powerful tool for enhancing the prediction capability of extreme weather and climate events in the Arctic," said YANG.