A peatland is a type of wetland where the soil is made mostly of decayed plant material, forming layers called peat. These wetlands form when plant matter does not fully break down because the soil is wet and lacks oxygen. Peatlands are unique landforms shaped mostly by living things rather than physical forces, and they often have distinct shapes and patterns on the surface.

The way peatlands form is mainly influenced by climate factors like rainfall and temperature. However, the shape of the land also plays a big role because wet areas are more common on flat ground and in low-lying areas. Peat can begin to form in different ways, such as when wetland conditions develop in forest soils, when lakes turn into land, or when peat forms on bare soil in areas once covered by glaciers. A peatland that is currently creating peat is called a mire. All mires have the same main feature: they are wet for at least part of the year, have peat forming, and support their own ecosystems.

Peatlands are the largest natural storage of carbon on land. They cover about 3 million square kilometers worldwide and absorb 0.37 gigatons (Gt) of carbon dioxide (CO₂) each year. Peat soils hold more than 600 Gt of carbon, which is more than all other plant types combined, including forests. In their natural state, peatlands help protect against floods and soil erosion, clean water, and help control the climate.

Peatlands are at risk due to human activities like harvesting peat for commercial use, draining wetlands, converting them into farmland (especially for palm oil in tropical regions), and fires. These fires are expected to happen more often as the climate changes. When peatlands are destroyed, the stored carbon is released into the atmosphere as greenhouse gases, making climate change worse.

Types

Scientists use the term "peatland" to describe any area where peat, a type of soil made from partially decayed plant material, covers the ground to a depth of at least 30 cm (12 in), even if the area is completely dry. A peatland that can still create new peat is called a mire. However, if a peatland has been drained and no longer forms new peat, it is not considered a mire.

There are two main types of mire: bog and fen. A bog is a type of mire that sits higher than the surrounding land and receives all its water only from rain (called ombrotrophic). A fen is a mire that is located on a slope, flat ground, or in a low area and gets most of its water from nearby soil or groundwater (called minerotrophic). Because of this, bogs are always acidic and have very few nutrients, while fens can be slightly acidic, neutral, or even slightly alkaline, and may have more or fewer nutrients. All mires start as fens when peat first forms, and some may later become bogs if the peat layer grows high enough to rise above the surrounding land.

A quagmire is a type of wetland that floats or feels soft and shaky underfoot, such as a floating mat of plants. It can be part of a stage in the development of a wetland. If a quagmire receives water only from rain, it may be called a quaking bog. If it gets water from groundwater or soil, it might be called a quagfen.

Some swamps can also be peatlands, such as peat swamp forests. Marshes, however, are not usually considered peatlands. Swamps are wetlands with tall, dense vegetation like trees or papyrus, and often have a forest canopy. Like fens, swamps typically have more nutrients and a higher pH level than bogs. Some bogs and fens may support small shrubs or trees growing on raised areas of peat. A marsh is a wetland where plants grow in soil that is not peat.

Global distribution

Peatlands are found all over the world. They are most common in high latitude areas of the Northern Hemisphere. Peatlands cover about 3% of Earth's surface, but it is hard to measure their exact size because different countries use different methods for land surveys. Mires form in places where water keeps organic material wet for long periods. The places where mires form depend on land shape, weather, soil type, living things, and time. The type of mire—bog, fen, marsh, or swamp—also depends on these factors.

The largest mire areas cover about 64% of Earth's peatlands. These are found in temperate, boreal, and subarctic regions of the Northern Hemisphere. In polar regions, mires are usually shallow because organic material builds up slowly, and they often include permafrost and palsas. Large areas of Canada, northern Europe, and northern Russia have boreal mires. In temperate regions, mires are often scattered due to past drainage and peat harvesting, but they can still cover large areas. One example is blanket bog, which forms in areas with very high rainfall, such as coastal regions of the north-east and south Pacific, and the north-west and north-east Atlantic. In sub-tropical areas, mires are rare and only found in the wettest places.

Mires can also be found in tropical regions, often under tropical rainforests, such as in Kalimantan, the Congo Basin, and the Amazon Basin. Tropical peat forms in coastal mangroves and high-altitude areas. Tropical mires form where heavy rainfall combines with poor drainage. These mires make up about 11% of Earth's peatlands, with more than half located in Southeast Asia. They are most common at low altitudes but can also be found in mountainous areas, such as in South America, Africa, and Papua New Guinea. Indonesia, especially on the islands of Sumatra, Kalimantan, and Papua, has one of the world's largest peatlands, covering about 24 million hectares. These areas store large amounts of carbon and support high levels of biodiversity. However, they face threats from deforestation and fires. In the early 2000s, the largest tropical mire was discovered in the Central Congo Basin, covering 145,500 square kilometers and storing up to 10 kilograms of carbon per square meter.

The total area of mires has decreased worldwide because of drainage for farming, logging, and peat harvesting. For example, more than 50% of Europe's original mire area—over 300,000 square kilometers—has been lost. Major losses have occurred in Russia, Finland, the Netherlands, the United Kingdom, Poland, and Belarus. A collection of peat research at the University of Minnesota Duluth includes references to studies on peat and peatlands worldwide.

Biochemical processes

Peatlands have special chemical properties that affect the life forms living there and the water that flows out. Peat holds many minerals because it has a lot of organic material. Minerals like calcium are often pulled into the peat, replacing hydrogen ions. As water moves through peat, it loses nutrients and becomes more acidic. Because of this, mires are usually low in nutrients and acidic unless groundwater adds more minerals.

Peat forms when more carbon enters the soil from dead plants than is lost through decay. This happens because waterlogged peat has little oxygen, which slows decay. Plants that grow in peatlands are often hard to break down because they have high levels of lignin and low nutrients. Over time, peat builds up, raising the ground above its original level. In temperate areas, peat can be more than 10 meters deep, while in tropical areas, it can be over 25 meters deep. A mire stops growing in height when the rate of peat decay matches the rate of new peat forming.

Although peatlands cover only 3% of Earth's land, they store a large amount of carbon—between 500 and 700 billion tons. This is more than half the carbon in the atmosphere. Peatlands exchange gases like carbon dioxide, methane, and nitrous oxide with the air. They can be harmed by too much nitrogen from farming or rain. Carbon is stored through photosynthesis, while carbon is lost through respiration by plants and decomposing material. Naturally, peatlands take in more carbon dioxide than they release, but they often release more methane and nitrous oxide. Over thousands of years, the carbon stored in peatlands has helped cool the atmosphere because carbon dioxide stays in the air longer than methane or nitrous oxide.

The water level in a peatland controls how much carbon is released. When heavy rain raises the water level, peat and its microbes are underwater, reducing oxygen and slowing carbon dioxide release. When the water level drops, like during a drought, more oxygen reaches microbes, speeding up decay and increasing carbon dioxide release. Methane levels also depend on water levels and temperature. When the water level is near the surface, anaerobic microbes thrive, producing methane. Methane is made by microbes in oxygen-free conditions below the water, while other microbes above the water break some methane down. Changes in water levels affect how much methane is made or destroyed. Warmer temperatures also increase methane release. A study in Alaska found methane levels can change by up to 300% seasonally due to wetter and warmer conditions from climate change.

Peatlands are valuable for studying past climates because they record environmental changes. They contain information about isotopes, pollutants, ancient plant parts, metals, and pollen. For example, carbon-14 dating can show how old peat is. Destroying peatlands releases carbon dioxide that could reveal important climate history. Many microbes live in peatlands because of the water supply and plant life. These include methane-producing microbes, algae, bacteria, and small aquatic animals, with Sphagnum moss being the most common.

Peat has a lot of organic material, with humic acid being the main type. Humic materials hold water, which helps create conditions without oxygen, increasing carbon storage. If peatlands dry from farming or use, the water level drops, allowing more oxygen and releasing carbon. If they dry completely, the ecosystem may change, becoming less diverse and barren. Humic acid forms when plant and animal matter breaks down. The organic material in humic acid can become a source of coal. Exposing peat to air too early causes organic matter to turn into carbon dioxide, which is released into the atmosphere.

Use by humans

Peatlands can hold records of past human activities and environments. These records may include human-made objects, as well as information about ancient environments and chemical data.

In modern times, humans use peatlands for many purposes, with agriculture and forestry being the most common. These activities cover about a quarter of the world’s peatland area. This often involves digging ditches to lower the water level, which helps increase the productivity of forests or make the land suitable for farming or grazing. In some areas, people use plants from peatlands for hay or grazing, or grow crops on land that has been changed. In Northern European countries like Russia, Sweden, Finland, Ireland, and the Baltic states, peat is also mined for energy.

Tropical peatlands cover 0.25% of Earth’s land but store 3% of all soil and forest carbon. Human activities, such as draining and cutting down tropical peat forests, release large amounts of carbon dioxide into the air. Fires that occur on dried peatlands release even more carbon dioxide. In the past, the economic value of tropical peatlands came from materials like wood, bark, resin, and latex, which were extracted without causing large carbon emissions. In Southeast Asia, peatlands are drained and cleared for uses such as producing palm oil and timber for export in developing countries. This releases stored carbon dioxide and stops the land from absorbing carbon again.

Tropical peatlands

Tropical peatlands are found mainly in Southeast Asia. Over the past few decades, more land has been used for farming, especially for growing palm oil and other crops. Large areas of these peatlands have been cleared and drained, which can cause the ground to sink, flooding, fires, and poor soil quality. Smaller-scale farming activities are also common in these areas and are often linked to poverty. These activities harm the peatlands and their environment.

The soil, water, and shape of Southeast Asian peatlands depend on the plants that grow there. These plants create conditions that support their own growth. This system is fragile and can be harmed by changes in water levels or the types of plants present. Most of these peatlands are in developing countries with growing populations. These areas are targeted for logging, paper production, and farming, which involve cutting down trees, draining land, and burning. Draining peatlands changes water levels, making them more likely to catch fire and lose soil. These changes harm plants and forests, reducing biodiversity in the short term and destroying habitats in the long term. People often do not understand how sensitive these peatlands are, which leads to failed farming projects and more pressure on remaining peatlands.

The plants in tropical peatlands vary based on climate and location. Mangrove woodlands grow in coastal areas with saltwater. Further inland, swamp forests are found, which include tall trees and plants like ferns. In the center of large peatlands, shrubs and thin trees called "padang" grow. Tropical peatlands have more types of trees and shrubs than other peatlands. Unlike peatlands in colder regions, which have moss, tropical peatlands are made mostly of tree and shrub material. The top layer is thick with leaves that have not fully broken down. Farming in these areas causes drainage and releases large amounts of carbon because it reduces the amount of plant material and speeds up decay. Unlike temperate wetlands, tropical peatlands support many fish species, some of which are found only in these areas and are at risk of disappearing.

Tropical peatlands cover only 0.2% of Earth’s land but release about 2 gigatonnes of CO₂ each year, which is 7% of global emissions from burning fossil fuels. These emissions increase when peatlands are drained or burned. A severe fire can release up to 4,000 tonnes of CO₂ per hectare. Fires in these areas are becoming more common due to land clearing and drainage. Over the past ten years, more than 2 million hectares of peatland in Southeast Asia alone were burned. These fires often last 1–3 months and release large amounts of CO₂.

Indonesia is heavily affected by peatland fires, especially during droughts linked to El Niño events. These droughts have become more frequent since 1982 because of increased farming and land use. During the 1997–1998 El Niño event, over 24,400 square kilometers of peatland in Indonesia were lost to fires, with 10,000 square kilometers burned in Kalimantan and Sumatra. CO₂ emissions from these fires were estimated at 0.81–2.57 gigatonnes, which is 13–40% of global fossil fuel emissions that year. Indonesia is now the third-largest source of global CO₂ emissions, mainly due to these fires. The 2015 El Niño event worsened conditions, as wildfires burned about 3 million hectares of forests and peatlands in Sumatra and Kalimantan, releasing 11.3 teragrams of CO₂ each day in September and October.

As the climate warms, fires are expected to become more frequent and severe. This is partly because of large-scale rice farming projects, like the Mega Rice Project in Indonesia, which started in the 1990s. This project drained 1 million hectares of peatland to grow rice. However, drought and soil acidification led to poor harvests, and the project was abandoned in 1999. Similar projects in China have also caused the loss of tropical wetlands.

Draining peatlands increases the risk of fires and can release an additional 30–100 tonnes of CO₂ per hectare each year if the water level drops by just 1 meter. Draining is the most significant and long-term threat to peatlands worldwide, especially in tropical regions.

Peatlands also release methane, a powerful greenhouse gas. However, subtropical wetlands may absorb more CO₂ than they release methane, which can help reduce global warming. Tropical peatlands are estimated to hold about 100 gigatonnes of carbon, which is more than half of the carbon in the atmosphere as CO₂. Over the past 1,000 years, these peatlands have accumulated carbon at a rate of about 40 grams per square meter each year.

Northern peatlands

Northern peatlands are found in cold climates like boreal and subarctic regions. These peatlands formed mainly during the Holocene period after glaciers from the Pleistocene era melted and moved away. In contrast, tropical peatlands are much older. Scientists estimate that northern peatlands hold about 1,055 gigatons of carbon.

Among all northern countries, Russia has the largest area of peatlands and is home to the world’s largest peatland, called The Great Vasyugan Mire. The Nakaikemi Wetland in southwest Honshu, Japan, is over 50,000 years old and has a depth of 45 meters. The Philippi Peatland in Greece likely has one of the deepest peat layers, reaching 190 meters.

Impacts on global climate

According to the IPCC Sixth Assessment Report, protecting and restoring wetlands and peatlands can help reduce greenhouse gas emissions. These actions offer benefits for both reducing emissions and helping communities adapt to climate changes, as well as supporting biodiversity.

Wetlands are areas where organic carbon is stored in living and dead plants, as well as in peat. This carbon can also be turned into carbon dioxide and methane. Three main factors help wetlands store carbon: high plant growth, high water levels, and slow breakdown of organic matter. Wetlands need enough water to function properly. When wetland soil is fully saturated with water, it creates conditions without oxygen, which helps store carbon but also releases methane.

Wetlands cover about 5 to 8 percent of Earth's land, but they hold 20 to 30 percent of the planet's soil carbon. Peatlands, a type of wetland, store the most soil organic carbon of all wetland types. However, wetlands can become sources of carbon instead of storing it, as decomposition within the ecosystem releases methane. Natural peatlands may not always cool the climate quickly because the cooling effect of storing carbon is sometimes balanced by methane emissions. Methane, though a strong greenhouse gas, stays in the atmosphere for only about 12 years. Over 300 years, the carbon stored in wetlands usually outweighs methane emissions, making wetlands net carbon and radiative sinks. Peatlands, therefore, help cool Earth's climate over long periods because methane is removed from the air quickly, while carbon dioxide is continuously absorbed. During the Holocene (the past 12,000 years), peatlands have been major carbon storage areas, absorbing between 5.6 and 38 grams of carbon per square meter each year. On average, northern peatlands today store about 20 to 30 grams of carbon per square meter annually.

Peatlands help protect permafrost in subarctic regions by slowing summer thawing and encouraging permafrost formation. As global temperatures rise, wetlands may become major sources of carbon because higher temperatures increase carbon dioxide emissions.

Compared to untilled cropland, wetlands can store about twice as much carbon. Carbon storage happens in both natural and constructed wetlands. Studies show that natural wetlands release less greenhouse gases than man-made wetlands, but man-made wetlands store more carbon. Restoring and protecting wetlands can improve their carbon storage abilities, though it takes many years for restored wetlands to match the carbon storage of peatlands and other natural wetlands.

The exchange of carbon between peatlands and the atmosphere is a major focus in ecology and biogeochemical studies. Draining peatlands for agriculture and forestry releases large amounts of greenhouse gases, especially carbon dioxide and methane. Drainage allows oxygen to enter peat, disrupting the balance between peat growth and breakdown. This causes peat to break down and release carbon into the atmosphere. Draining peatlands for farming changes them from carbon storage areas to carbon emitters. While methane emissions from peatlands may decrease after drainage, the overall emissions from drained peatlands are often higher because peat accumulates slowly. Peatland carbon is described as "irrecoverable," meaning that if lost due to drainage, it cannot be recovered within timeframes relevant to climate goals.

If managed in ways that preserve the water conditions of wetlands, human use of these areas can avoid significant greenhouse gas emissions. However, continued drainage increases carbon release, contributing to global warming. By 2016, drained peatlands were estimated to account for about 10 percent of all greenhouse gas emissions from agriculture and forestry.

Palm oil has become one of the world's largest crops. Compared to other crops, palm oil is considered highly efficient for producing vegetable oil and biofuel, requiring only 0.26 hectares of land to produce 1 ton of oil. This efficiency has made palm oil a popular crop in low-income countries, providing economic opportunities for communities. In countries like Indonesia and Malaysia, where palm oil is a major export, many small farmers have gained economic success through palm oil plantations. However, the land used for plantations is often rich in carbon and supports biodiverse ecosystems.

Palm oil plantations have replaced much of the forested peatlands in Southeast Asia. By 2006, about 47 percent of peatlands in the region had been deforested. In their natural state, peatlands are waterlogged with high water levels, making the soil inefficient for farming. To create usable soil for plantations, peatlands in tropical regions like Indonesia and Malaysia are drained and cleared.

Peatland forests used for palm oil production store large amounts of carbon both above and below ground, holding at least 42,069 million metric tonnes of soil carbon. Exploiting this land raises environmental concerns, including increased greenhouse gas emissions, fire risks, and reduced biodiversity. Greenhouse gas emissions from palm oil grown on peatlands are estimated to range between 12.4 (best case) and 76.6 tons of carbon dioxide per hectare (worst case). Tropical peatlands converted to palm oil plantations can remain a net source of carbon to the atmosphere for up to 12 years.

In their natural state, peatlands are resistant to fire. However, draining peatlands for plantations creates a dry layer of flammable peat. Because peat is rich in carbon, fires in drained peatlands release large amounts of carbon dioxide and toxic smoke into the air. These fires increase greenhouse gas emissions and cause thousands of deaths each year.

Deforestation and drainage reduce biodiversity, making ecosystems less resilient to changes. Ecosystems that are not diverse are more vulnerable to extreme weather and less likely to recover from fires.

Some peatlands are drying due to

Management and rehabilitation

The United Nations Convention on Biological Diversity emphasizes the importance of peatlands as ecosystems that must be kept safe and protected. This agreement asks governments at all levels to create plans for protecting and managing wetland areas. Wetlands are also protected by the 1971 Ramsar Convention.

Restoration efforts often involve closing drainage channels in peatlands and letting natural plants grow again. In North America and Europe, projects usually focus on adding water back to peatlands and planting native species. This helps reduce carbon emissions quickly, and over time, new plant growth adds organic material that supports peat formation. UNEP is helping restore peatlands in Indonesia.

Peat extraction is not allowed in Chile since April 2024.

The Global Peatlands Initiative was started in 2016 by 13 groups at the UNFCCC COP in Marrakech, Morocco. Its goal is to protect peatlands, which hold the largest amount of organic carbon on land, and stop this carbon from entering the atmosphere.

Members of the Initiative work together using their knowledge to improve the protection, restoration, and management of peatlands. This effort helps achieve several Sustainable Development Goals (SDGs), including keeping carbon stored in the ground (SDG 13), reducing health risks from air pollution caused by burning drained peatlands (SDG 3), protecting water ecosystems and improving water quality (SDG 6), and conserving ecosystems and threatened species to protect life on land (SDG 15).