Hidden Roots of a Warming Arctic: How Tundra Plants Could Decide the Climate Future

From space, the Arctic story looks simple. Satellites see the tundra turning greener as shrubs spread, trees push north, and the growing season lengthens. It looks like a landscape coming to life. But a major new review says the most important part of that story is the part satellites cannot see at all: what is happening underground, where plant roots meet frozen soil.

The review, published in Nature Reviews Earth & Environment and led by Rebecca Hewitt of Amherst College, with Gesche Blume-Werry of Umeå University and Thomas Parker of The James Hutton Institute, brings together researchers from eleven organisations. Its message is both clear and unsettling. Roots and the thin zone of soil around them — the rhizosphere — may help decide whether the Arctic becomes a net source of greenhouse gases or a place that still stores carbon, even as it warms. That question matters far beyond the far north, because the carbon locked in Arctic soils is enormous.

A frozen carbon bank twice the size of the atmosphere

Permafrost is ground that has stayed frozen for at least two years, and in much of the Arctic for thousands of years. Over that long time, dead plants, animals and microbes have built up in its soils instead of fully decomposing. The result is a frozen carbon bank.

The review repeats the widely used estimate: northern permafrost soils hold about 1,460 to 1,600 billion tonnes of organic carbon. That is roughly twice as much carbon as is currently in the atmosphere, and more than 40 percent of all the carbon stored in the world's terrestrial soils. Most of it sits in the top few metres, but significant amounts lie deeper.

That scale is why scientists talk about a feedback loop: thaw lets microbes break down old organic matter, releasing carbon dioxide and methane, which warms the climate and thaws more permafrost. The question is how much, how fast, and whether new plant growth can offset it. The review argues roots sit at the centre of that balance.

Understanding this feedback is easier when the basic warming process is clear. Our earlier explainer on the greenhouse effect and how it warms the planet sets out why extra carbon dioxide and methane in the air trap more heat, and why even small-sounding changes in a huge carbon store can have global effects.

Greening above ground, change below ground

Arctic greening is real, but it is only half the picture. As temperatures rise, shrubs grow taller, spread into new areas, and push their roots deeper. Trees advance at the treeline. The growing season shifts, with plants starting earlier or growing for longer in some places. All of this changes what happens below the surface.

In Arctic ecosystems, a surprisingly large share of plant biomass is underground. Roots take up water and nutrients, die and add organic matter to the soil, and release compounds into the soil while alive. The review finds warming and thaw are already changing root productivity, depth, seasonal growth and plant-soil interactions.

That matters because deeper roots can reach soil layers previously frozen and untouched by living plants. As the active layer — the top layer that thaws each summer — deepens, roots follow it down into ground that has stored carbon for millennia, bringing fresh energy, water and microbes with them.

The rhizosphere: a tiny zone with an outsized effect

The rhizosphere is the narrow zone of soil directly influenced by a root, often only a few millimetres wide. It sounds too small to matter to the global climate. In practice, it is one of the busiest places in the soil.

Living roots release sugars, organic acids and amino acids, collectively called rhizodeposits. These feed microbes, and can stimulate them to break down older soil organic matter faster than they otherwise would — a process called rhizosphere priming.

The review highlights priming as a key mechanism, and also as a warning against simple predictions. Experiments cited in the review show that plant-derived compounds can speed up the decomposition of organic matter in Arctic permafrost soils. Yet the effect is not the same everywhere. Peat soils in parts of the circumpolar Arctic, for example, appear to resist priming by plant compounds, suggesting that water, minerals and soil chemistry strongly shape the outcome. A root in one kind of soil may unlock old carbon; a similar root in another may have little such effect.

Roots also work with fungi. Many Arctic plants form partnerships with mycorrhizal fungi, trading carbon from photosynthesis for nutrients gathered by fungal threads. Those partnerships affect how much carbon stays in plant and fungal biomass, how much reaches the soil, and how nutrients cycle. The review notes these trade-offs are poorly captured in many large-scale models, even though they can change the direction of the carbon balance locally.

Roots can both store carbon and release it

This dual role is the heart of the review, and the reason it resists a simple headline. Roots can help lock carbon away. More plant growth means more leaves and stems that fall to the ground, more roots that die and become soil organic matter, and more living biomass that holds carbon for a time. In a warming Arctic, that extra growth is real and visible.

At the same time, roots can speed carbon loss. By feeding microbes, changing soil moisture and chemistry, and reaching newly thawed layers, they can accelerate the breakdown of old carbon into carbon dioxide and methane. Methane is especially important here. It is released in wet, oxygen-poor soils, and over shorter timescales it traps far more heat per tonne than carbon dioxide. A landscape that looks greener and healthier from above can therefore still be losing carbon below.

Which effect wins depends on the plant species, the soil type, how wet or dry the ground is, how deep the thaw goes, and how long the process runs. Shrub expansion in a dry upland site will not behave like sedge growth in a wet lowland, and neither will behave like a forest advancing into tundra. The review's central argument is that without understanding those local, belowground differences, global estimates will remain uncertain — and may even get the sign wrong, calling a source a sink or vice versa.

That uncertainty connects directly to wider climate monitoring. The latest global climate report on Earth's vital signs shows many indicators moving in the wrong direction at once, from temperature to ice loss. The Arctic root story helps explain why one region's carbon balance is so hard to pin down, even when the overall warming trend is clear.

Why climate models have missed the roots

If roots are so important, why have they received so little attention? The review points to a practical problem: roots are hard to measure. Satellites can track leaf area and greenness across the whole Arctic, but they cannot see root depth, root turnover or microbial activity a metre underground. Fieldwork in the Arctic is expensive, seasonal and often limited to the short summer. Digging up roots disturbs the very system being studied.

As a result, Arctic root traits are poorly represented in global plant trait databases, the review finds. Rooting depth distributions influence modelled carbon emissions, but they cannot be reliably inferred from aboveground vegetation type alone. Two plant communities that look similar from a drone or satellite may have very different root systems, and therefore very different effects on soil carbon.

Models have also tended to treat thaw as gradual and top-down. Real thaw is messier: ice-rich ground can collapse suddenly, forming thaw ponds and slumps that expose deep carbon quickly.

What thaw means for Arctic communities and the wider world

The stakes are not abstract. For Indigenous and northern communities, permafrost thaw already damages homes, roads, runways and water systems as the ground subsides and shifts. Thaw changes hunting and travel routes, alters wetlands and lakes, and reshapes the plants and animals people depend on. A review focused on roots may sound academic, but its findings feed into forecasts that communities, planners and governments use to prepare for those changes.

For the rest of the world, permafrost release adds to warming over decades and centuries. Every additional tonne of carbon dioxide and methane from thaw makes stabilising the climate harder — which is why a story about roots belongs in a general environment section, not only in specialist journals.

It also connects to patterns closer to home for many readers. When cities trap heat, for example, the local warming feedback works differently but follows a similar logic: a landscape change alters heat and moisture, which then reinforces the change. Our guide to urban heat islands and why cities run hotter than surrounding countryside explains that local feedback in detail, and shows why small-scale surface processes can have outsized effects on the climate people actually experience.

What scientists want to study next

The review team was assembled through the International Arctic Science Committee ahead of the 5th International Polar Year in 2032–2033, a major international research effort. The authors use the review as a call to action: put belowground processes at the centre of Arctic research in the run-up to that year, rather than treating them as an afterthought to aboveground greening.

In practice, that means more year-round measurements, including winter, when much Arctic carbon loss occurs but fieldwork is hardest. It means standardised root measurements across sites, so results can be compared. It means experiments that warm soils, add or remove roots, and track microbes and gases over several years, not just one season. And it means bringing root traits, mycorrhizal partnerships and priming into Earth system models in a testable way, so modellers can show whether the new detail actually improves predictions.

What to watch — and what not to overclaim

Readers following this story should watch for three developments. First, new field studies that measure roots and soil gases together through winter and summer, rather than inferring one from the other. Second, model updates that explicitly include root depth and priming, with clear statements about whether they change the projected Arctic carbon balance. Third, results from the International Polar Year programme, which should bring far more coordinated belowground data than any single team could gather alone.

The most honest summary is also the most useful. The Arctic is warming fast, its frozen soils hold roughly twice as much carbon as the atmosphere, and its plants are growing and rooting deeper into ground that is thawing. Those roots can build soil carbon and can also help microbes release it. Until we measure that underground balance properly, our picture of the future climate will remain incomplete — not because the science is failing, but because we have been looking mostly at the leaves while the decisive action happens in the soil.

Sources and further reading

Hewitt, R. E. et al., "The Arctic carbon cycle response to changing root and rhizosphere processes amid greening and permafrost thaw," Nature Reviews Earth & Environment (2026). DOI: 10.1038/s43017-026-00832-9.

Phys.org, "Arctic plant roots may play key role in climate change," 2 November 2026.

The James Hutton Institute, "Review reveals importance of hidden Arctic roots for climate change," 30 October 2026.