Cerrado wetlands: the hidden carbon time bomb for the global climate

When people think of climate protection in South America, their minds almost automatically turn to the rainforest. Yet alongside the well-known Amazon region, there is a second, quieter giant: the Cerrado, an immense savannah landscape with hidden peatlands and wetlands. New research now shows that these waterlogged soils in particular lock away a remarkable quantity of carbon – and that further drainage could turn them into a ticking time bomb for the global climate.

An overlooked hotspot for stored carbon

The Cerrado covers roughly a quarter of Brazil, spanning more than two million square kilometres. For a long time, it was viewed chiefly as an agricultural frontier: soya, cattle and sugar cane. In scientific terms, it remained overshadowed by tropical rainforests. A study published in March 2026 now corrects that perception.

Researchers from Brazil and the United States collected deep soil samples from seven sites, in some cases reaching depths of four metres. Rather than focusing only on the upper layers of soil, as many earlier studies had done, the team examined the depths where organic material has accumulated over millennia.

“Some Cerrado wetlands contain up to 1,200 tonnes of carbon per hectare – around six times the above-ground biomass of many Amazon forests.”

When extrapolated, these scattered wetlands could hold about one fifth of the total carbon stock of the Amazon region. This is far more than an academic figure: international climate models rely on such data to determine how much CO₂ humanity can still emit. If underground carbon stores are underestimated, those calculations become unreliable.

Why the Cerrado savannah stores so much carbon

For many people, savannah suggests dry grass, bushfires and relatively poor soils. However, a different picture emerges beneath the surface in the Cerrado. Wet hollows, spring-fed areas and slow-moving streams – known as veredas – run through its drier expanses.

These areas support specialised plant species, often with deep roots and dense root mats. Each year, plant material is deposited and remains waterlogged instead of decomposing completely. Over very long periods, this creates peat-like, organic soils with exceptionally high carbon content.

• deep, water-saturated soils
• little oxygen and slow decomposition
• a continuous supply of plant remains
• layer-by-layer accumulation over thousands of years

The result can appear unremarkable: a marshy depression, palms and grasses. Beneath it, however, lies an archive of stored carbon, some of it dating back to prehistoric times.

How water levels and oxygen shape the climate

The key process behind this carbon store lies in the relationship between water and oxygen. As long as soils remain saturated for much of the year, microorganisms lack the oxygen needed to break down dead plant material quickly. Decomposition slows dramatically, leaving carbon locked in the ground.

Once water levels fall, however, the system can tip. If a wetland dries out or is deliberately drained, air penetrates deeper soil layers. Microorganisms become more active, decomposition accelerates, and CO₂ – as well as, in some cases, methane – escapes into the atmosphere.

“What was stored over thousands of years can be released again within just a few decades – and once the process has begun, it is difficult to stop.”

Measurements by the research teams indicate that around 70 per cent of greenhouse-gas emissions from these soils occur during the dry season. As global warming makes drought periods longer and more intense, the danger of a domino effect increases. The Cerrado could shift from a climate shield to an accelerator of climate change.

Veredas: lifelines and climate buffers

The Cerrado’s characteristic wetlands, the veredas, extend through the landscape like veins. They occur alongside small rivers or in depressions where groundwater reaches the surface. Dense stands of palms, grasses and shrubs are typical, continually adding organic material.

Alongside their role as carbon sinks, they fulfil several functions at once:

• headwaters for major river systems in Brazil
• filters for nutrients and pollutants in water
• habitats for specialised and, in some cases, threatened species
• buffers against droughts and floods in neighbouring regions

If these wetlands are lost, it is not only the carbon store that suffers. Water availability in faraway regions also begins to decline, including parts of the Amazon region that depend on water from the Cerrado.

More than a savannah: South America’s climate factor and “water tower”

The Cerrado is estimated to feed the headwaters of two thirds of Brazil’s major rivers. This makes it the water tower of an entire continent. Major urban areas, reservoirs supplying drinking water and energy, and industrial zones all depend on this system.

“Anyone who sacrifices the Cerrado is not only sawing through their own water supply, but also undermining the stability of the Amazon region.”

At the same time, the region is among the world’s most species-rich types of savannah. More than 12,000 plant species have been recorded, many of which occur nowhere else. Numerous animals – from giant anteaters and rare birds to reptiles – are adapted to the mosaic of dry and wet habitats.

This combination of water regulation, carbon storage and biodiversity makes the Cerrado an ecosystem of global importance that has so far been greatly undervalued in international debate.

Agriculture is spreading into wetlands – with consequences for the climate

Despite this role, the Cerrado has for decades been treated as a “biological buffer”: activities considered too sensitive in the Amazon, such as clearance and large-scale development, are moved into the savannah. Vast areas have consequently been converted into soya fields, maize crops and pasture. The effects on wetlands are direct.

To make fields and grazing land easier to manage, farmers dig drainage ditches, lower the water table and divert water. This drainage destroys the very mechanism that has kept these soils wet for thousands of years and protected their carbon.

“The region functions as a sacrificed buffer for agriculture – yet in doing so, Brazil is putting at risk the water source that also supports the rainforest.”

The research demonstrates how closely all these elements are connected: less water in the Cerrado means less moisture in air flows towards the Amazon. If stored carbon escapes at the same time, the climate warms further and droughts intensify – creating a feedback loop that is hard to halt.

Is protection on paper enough?

Protected areas and legal requirements for certain wetland habitats do exist. In practice, however, they remain incomplete and often focus only on land that is directly wet.

What is crucial is protecting the entire catchment area: the landscape from which a wetland receives its water. If surrounding forests are cleared, soils compacted or rivers diverted, even an apparently protected peatland will gradually dry out.

Problem	Consequence for wetlands
Drainage ditches	Faster water run-off, falling groundwater levels
Monocultures and soil compaction	Less infiltration, greater surface run-off
Overgrazing	Destruction of vegetation cover, erosion
Climate warming and longer dry periods	Longer periods with oxygen in the soil, greater CO₂ release

What could be done – and what is at stake

The study provides not only figures, but also arguments for specific action. Three priorities stand out:

• Protecting the water system: Protected areas must include headwater zones, tributaries and aquifers; otherwise, veredas can dry out unnoticed.
• Adapting agricultural policy: Support schemes that promote intensive soya production without accounting for water and carbon stores create hidden climate costs.
• Including soils in climate models: National and international CO₂ accounts should include these soils so that the global carbon budget is not artificially made to look better than it is.

For Europe, this is not a distant marginal issue. Large quantities of soya from the Cerrado ultimately end up in animal feed for German and other European farms. Consumer choices and trade agreements therefore directly influence the future of these wet savannahs.

Key terms and risks explained

When people refer to “carbon storage in soils”, they are mainly referring to organic matter: dead roots, leaves and woody debris. Flooded with water and poorly supplied with oxygen, these materials decompose extremely slowly, forming a dark layer resembling humus or peat. Every centimetre of this layer contains measurable amounts of carbon.

The situation becomes critical when land use and the climate change:

• Permanent drainage turns soil into a CO₂ source.
• Fires smouldering in dried-out peat soils release additional vast quantities of carbon.
• Combined effects – drought, agriculture and fire – drive the process further and make a return to the original state almost impossible.

It is precisely this combination that makes the Cerrado so vulnerable. Decisions made today about land use, agricultural subsidies or trade agreements also indirectly affect this underground carbon archive – and determine how much room for manoeuvre remains in global climate policy.