Arctic Registers Record Heat: 1.60°C Above 1991–2020 Mean as Melting, Greening and ‘Rusting Rivers’ Multiply Impacts

The US National Oceanic and Atmospheric Administration's annual Arctic Report Card finds the Arctic experienced its warmest year on record from October 2024 through September 2025, averaging 1.60°C above the 1991–2020 mean. Drawing on datasets extending back to 1900, the report documents accelerating change across sea ice, ice sheets, ecosystems and the Arctic water cycle.

Unprecedented Warming

The year included the Arctic's warmest autumn, second-warmest winter and third-warmest summer since 1900. Co-author Tom Ballinger of the University of Alaska described the speed of warming as "certainly alarming," calling the trend "seemingly unprecedented in recent times and maybe back thousands of years." The primary driver is human-caused greenhouse gas emissions, amplified locally by feedbacks known as Arctic Amplification.

How Arctic Amplification Works

Higher temperatures raise atmospheric water vapor, which traps more heat. At the same time, retreating reflective sea ice exposes darker ocean water that absorbs additional solar energy, reinforcing warming.

Sea-Ice Loss and Wildlife Impacts

Spring 2025 recorded the smallest annual sea-ice maximum in the 47-year satellite record (March 2025). Walt Meier of the National Snow and Ice Data Center warned this is an immediate threat to polar bears, seals and walrus, which rely on ice as a platform for hunting, travel and breeding. Climate models indicate the Arctic could experience a summer with virtually no sea ice by around 2040 or sooner, with major ecological and socioeconomic consequences.

Ocean Circulation and Greenland Ice Melt

Melting sea ice, accelerated Greenland Ice Sheet runoff and increased Arctic precipitation add freshwater to the North Atlantic. That freshwater lowers surface salinity and density, making it harder for surface waters to sink and help drive the Atlantic Meridional Overturning Circulation (including the Gulf Stream). Changes to these currents can influence European climate and broader weather patterns. Greenland's land-ice loss also remains a significant contributor to global sea-level rise and can alter the timing of marine food webs—boosting plankton in some areas while creating mismatches between food availability and species life cycles.

Hydrological Intensification and Greening

The October 2024–September 2025 "water year" recorded record-high spring precipitation and ranked among the five wettest seasons in datasets back to 1950. Warmer, wetter conditions are accelerating the "borealization" or greening of tundra: 2025's circumpolar mean maximum tundra greenness was the third highest in the 26-year satellite record, and the five highest values have occurred in the last six years.

Permafrost Thaw and Discolored Rivers

Permafrost thaw is driving biogeochemical changes across Arctic watersheds. The report identified more than 200 streams and rivers that appeared visibly orange this year—an effect often termed "rusting rivers"—caused by iron and other materials released from thawing soils. These discolored waterways show increased acidity and metal concentrations that degrade water quality and threaten aquatic biodiversity.

What This Means

Together these trends—rapid warming, collapsing sea ice, accelerating melt from Greenland, intensified precipitation, tundra greening and permafrost thaw—constitute cascading impacts with local and global consequences: threats to Arctic communities and wildlife, contributions to sea-level rise, and potential shifts in weather and ocean circulation far beyond the Arctic.

"The rate and breadth of change across the Arctic are troubling and demonstrate how quickly systemic impacts can cascade," the report concludes.