Peatlands store an enormous amount of carbon. Covering only 3% of the land surface, they store more than 450 gigatonnes of carbon - more than stored by forests (which cover 30% of the land surface). Drained peatlands cause numerous negative environmental impacts such as greenhouse gas emission, nutrient leaching, subsidence and loss of biodiversity. Although only 0.3% of all peatlands are drained, peatland drainage is estimated to be responsible for 6% of all human greenhouse gas emission. By making soils waterlogged when re-wetting peatlands, decomposition of organic matter (~50% carbon) will almost cease, and hence carbon will no longer escape into the atmosphere as carbon dioxide. Peatland rewetting can significantly reduce environmental impacts caused by drainage by restoring hydrological buffering  and reducing the water table's sensitivity to atmospheric evaporative demand. Due to the drainage of soils for agriculture in many areas, the peat soil depth and water quality has dropped significantly over the years. These problems are mitigated by re-wetting peatlands. As such, they can also make installations against rising sea levels (levees, pumps) unnecessary. Wet bogs act as nitrogen sinks, whereas mineralisation and fertilisation from agriculture on drained bogs produces nitrogen run-off into nearby waters.