Permafrost is ground that stays frozen for years, and across the Arctic it holds vast stores of organic matter. As the ground thaws, it changes rivers, plants and the carbon cycle. Two NOAA Arctic Report Cards, from 2024 and 2025, show how those changes are playing out in the tundra.
What does the Arctic Report Card measure?
The Arctic Report Card is NOAA’s annual, peer-reviewed assessment of the Arctic environment. It brings together scientists from many countries to report on conditions such as temperature, sea ice, permafrost, vegetation and the carbon cycle. The findings below come from the 2024 and 2025 editions.
How do the 2024 and 2025 reports differ?
The two editions cover different ground. The 2024 report included a dedicated chapter on terrestrial carbon cycling and was written with research from more than 97 scientists in 11 countries. The 2025 report, summarized by the WMO, was written by 112 scientists from 13 countries and ranges across the whole Arctic system, with the rusting rivers and tundra greenness among its findings. Because the warming figures come from different reports, they use different baselines: up to four times the global rate in one, more than double the global rate since 2006 in the other. They should not be treated as a contradiction or merged into one number.
What should readers keep in mind?
Three cautions apply. First, the carbon finding depends on counting wildfire emissions, so it describes a year with heavy fire and not a permanent state. Second, greening and carbon loss can happen together, so one trend does not cancel the other. Third, the rusting rivers finding concerns more than 200 watersheds in Arctic Alaska, which is a regional result and should not be read as a statement about every Arctic river.
What is permafrost?
Permafrost is soil, rock or sediment that remains frozen for at least two consecutive years. In the Arctic it underlies large areas of tundra. When it thaws, material locked in the ground, including carbon and metals, can be released. The Arctic Report Card tracks permafrost temperatures because warming ground is a leading sign of this change.
What did the 2024 report find about carbon?
The 2024 Arctic Report Card included a chapter titled Arctic Terrestrial Carbon Cycling. According to a summary from Woodwell Climate Research Center, the report found that when wildfire emissions are included, the Arctic tundra shifted from storing carbon to being a source of carbon emissions to the atmosphere. The Arctic had acted as a carbon sink for thousands of years. The chapter links increased regional emissions to thawing permafrost, wildfires, and changes in plants and microbes. The finding bears on the carbon sink role that northern ecosystems have long played.
How warm was the ground in 2024?
Alaska recorded its second-warmest average yearly permafrost temperatures on record in 2024. It was also the second-highest year for wildfire emissions north of the Arctic Circle. Lead author Sue Natali said the Arctic is warming at a rate up to four times the global rate. The assessment drew on research from more than 97 scientists in 11 countries.
What are rusting rivers?
The 2025 report, as summarized by the World Meteorological Organization, describes rivers and streams turning orange as permafrost thaws. More than 200 Arctic Alaska watersheds have been affected over the past decade. Rusting rivers have higher acidity and toxic metal levels, which degrade water quality and harm aquatic habitats. The orange color is a visible warning that something in the ground has changed.
Why does thawing release metals?
The sources describe the outcome and not the chemistry. The general idea is that thaw exposes minerals in the ground to water and air, and the reaction releases acid and metals into streams. We keep to the report’s findings: higher acidity and toxic metal levels in affected waters.
Is the Arctic getting greener?
Yes, in a sense. The greening of the Arctic was first detected in the late 1990s. In 2025, maximum Arctic tundra greenness was the third highest in the 26-year satellite record. More plant growth might seem like a benefit, but the report treats greening as part of a system that affects habitats, permafrost and the carbon cycle, so the net effect on carbon is not simple. The 2024 finding that tundra became a net source when wildfire is included shows that plant growth alone does not decide the balance.
How do wildfires change the picture?
Wildfire emissions are included in the 2024 tundra finding. The report notes that 2024 was the second-highest year for wildfire emissions north of the Arctic Circle. Fires release stored carbon quickly, and they can also speed up thaw by removing the insulating vegetation and soil layers. The second effect is a general mechanism and is not stated in the pages we consulted.
What does this mean for climate?
If the Arctic adds carbon to the air instead of removing it, the world has an additional source to account for alongside human emissions. The researchers describe measuring these emissions at scale as a step needed to inform mitigation and adaptation. For the human side of the ledger, see our report on global CO2 emissions, and for the wider trend, see climate change.
Frequently asked questions
Is the Arctic tundra now a carbon source?
When wildfire emissions are included, the 2024 Arctic Report Card found it shifted from storing carbon to being a source.
What causes rusting rivers?
Thawing permafrost, according to the 2025 report. The rivers have higher acidity and toxic metal levels.
How fast is the Arctic warming?
Up to four times the global rate according to the 2024 report’s lead author, and more than double the global rate since 2006 according to the 2025 summary.
Do the two reports disagree on warming?
No. They report different measures: up to four times the global rate in the 2024 report, and more than double the global rate since 2006 in the 2025 summary.
Is Arctic greening a good sign?
It is a change that affects habitats, permafrost and the carbon cycle, so its overall effect is not simple.