Cerrado wetlands: the hidden carbon bomb beneath South America’s savannah

When people think about climate protection in South America, the rainforest is almost always the first place that comes to mind. Yet alongside the celebrated Amazon region, there is another, quieter giant: the Cerrado, an immense savannah landscape containing concealed peatlands and wetlands. New research now indicates that these waterlogged soils lock away a remarkable quantity of carbon - and that continued drainage could turn them into a ticking 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 regarded chiefly as an agricultural frontier for soya, cattle and sugar cane. In scientific terms, it remained overshadowed by tropical rainforests. A study published in March 2026 now corrects that picture.

Researchers from Brazil and the United States collected deep soil samples at seven sites, in some cases reaching depths of four metres. Rather than limiting their work to the upper soil layers, as many earlier studies had done, the team investigated the depths where organic matter 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.”

Extrapolated across the landscape, these scattered wetlands could hold about one fifth of the Amazon region’s total carbon stock. This is more than an academic statistic: international climate models rely on such figures to determine how much CO₂ humanity can still emit. If carbon stored in soils has been underestimated, those calculations become unstable.

Why this savannah stores so much carbon

For many people, savannah evokes dry grass, bushfires and relatively poor soils. The Cerrado presents a different picture once the ground beneath the surface is considered. Moist depressions, spring-fed areas and slow-moving streams - known as veredas - run between its drier parts.

These areas support specialised plant species, often with deep roots and dense root mats. Each year, they add plant material that remains waterlogged rather than decomposing completely. Over extremely long periods, this forms 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 visible landscape may seem unremarkable: a marshy hollow, palms and grasses. Beneath it, however, lies an archive of locked-up carbon, in some cases dating back to prehistoric times.

How water levels and oxygen influence the climate

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

Once water levels fall, the system shifts. If a wetland dries out or is deliberately drained, air penetrates deeper layers of soil. Microorganisms become more active, decomposition speeds up, and CO₂ - along with methane in some cases - is released into the atmosphere.

“What has been stored over thousands of years can be released again within just a few decades - and once this process begins, it is difficult to stop.”

Measurements by the research teams show that around 70 per cent of greenhouse-gas emissions from these soils occur during the dry season. As droughts become longer and more intense with global warming, the danger of a domino effect grows. The Cerrado could shift from a climate safeguard to an amplifier of climate change.

Veredas: lifelines and climate buffers

The Cerrado’s characteristic wetlands, the veredas, run through the landscape like veins. They occur along small rivers and in hollows where groundwater reaches the surface. Dense stands of palms, grasses and shrubs are typical, continually supplying organic material.

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

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

Losing these wetlands would damage more than the carbon store. Water availability in distant areas would also come under pressure, 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 regions 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 one of the most biodiverse savannah types on Earth. More than 12,000 plant species have been documented, many of which occur nowhere else. Numerous animal species - from giant anteaters and rare birds to reptiles - are adapted to its mosaic of dry and wet zones.

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

Agriculture is pushing 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 projects, are transferred to the savannah. Vast areas have consequently been converted into soya fields, maize farms and pasture. The effects on wetlands are immediate.

To manage fields and grazing land more easily, farmers dig ditches, lower groundwater levels and divert water. This drainage directly destroys the process that has kept the soils wet for thousands of years and protected their carbon.

“The region acts as a sacrificed buffer for agriculture - yet in doing so, Brazil is putting at risk the very water source that also sustains the rainforest.”

The research demonstrates how closely linked all these elements are: less water in the Cerrado means less moisture in air currents moving 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 protected status on paper enough?

Protected areas and legal requirements for certain wetland habitats do exist. In practice, however, they remain incomplete and often concentrate only on the areas that are immediately wet.

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

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 springs, tributaries and groundwater aquifers; otherwise, veredas can dry out unnoticed.
• Adjusting agricultural policy: Support schemes that promote intensive soya cultivation without accounting for water and carbon stores create hidden climate costs.
• Including soils in climate models: National and international CO₂ accounts should incorporate these soils so that the global carbon budget is not 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 used by German and other European farms. Consumer choices and trade agreements therefore directly affect the future of these wet savannahs.

Key terms and risks explained

When referring to “carbon stored in soil”, this mainly means organic matter: dead roots, leaves and wood residues. Held back by water and poorly supplied with oxygen, these materials decompose extremely slowly, building up 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 the 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 sensitive. Decisions made today about land use, agricultural subsidies or trade agreements also indirectly affect this underground carbon archive - and influence how much room for manoeuvre the world has left in climate policy.