A peat bog is a wetland where waterlogged conditions keep dead plant material from fully decomposing. Because the ground is saturated, there’s very little oxygen, and the microbes that normally break down plants can’t work efficiently. Over thousands of years, the partly decayed moss, sedges, and other vegetation piles up as peat, a dense, brown, spongy material. Peat accumulates very slowly, usually about a millimeter per year, so a bog several meters deep can be many thousands of years old.
Bogs are often fed mainly by rainfall rather than groundwater, which makes them low in nutrients and acidic. That favors specialized plants like sphagnum moss (the main peat builder), cranberries, and carnivorous plants such as sundews and pitcher plants.
Why they matter for the planet
- Carbon storage: Peatlands cover only about 3% of Earth’s land surface but store roughly twice as much carbon as all the world’s forests combined. This is one of the largest natural carbon stores on land.
- Climate risk when damaged: When peatlands are drained for farming, forestry, or peat extraction, the peat dries out and decomposes or burns, releasing stored carbon as CO₂. Drained and degraded peatlands are estimated to produce several percent of global human-caused emissions. Peat fires can smolder underground for months and are very hard to put out.
- Water regulation: Peat acts like a giant sponge, absorbing rainfall and releasing it slowly. This helps reduce flooding downstream and maintain water flow in dry periods. Many peatland catchments also supply clean drinking water.
- Biodiversity: Bogs support rare and specialized species, including migratory birds, insects, and plants found almost nowhere else.
- Historical archives: The acidic, oxygen-poor conditions preserve things remarkably well. Pollen layers reveal past climates and vegetation, and bogs have preserved ancient wooden structures and even human remains like Tollund Man in Denmark.
A nuance on methane
Natural peatlands do emit some methane, a potent greenhouse gas. But over long timescales, the carbon they lock away outweighs this, so intact peatlands are generally considered a net climate benefit. Protecting them and rewetting drained ones is widely seen as a cost-effective climate strategy.
Peatlands are found worldwide, with major concentrations in Canada, Russia, Indonesia, northern Europe, and the Congo Basin, which has one of the largest tropical peatlands.
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