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Causes for change:
- Natural: wetlands (72%)
- Natural: termites (12.5%)
- Natural: ocean (6%)
- Natural: other (9.5%)
- Natural: recent global warming also releases methane in the tundra that has been "locked" in frozen ground (positive climate feedback)
- Natural: potential release of large amounts of gas hydrates from submarine icy lenses could happen, if current warming persists (at which point this actually happens is currently unknown)
- Natural: a natural gas seep off-shore Santa Barbara releases significant amounts though most may be dissolved in water, unless it is transported very quickly to the sea surface
- Human: coal mining, natural gas, petroleum industry (27%)
- Human: rice paddies (16%)
- Human: cattle farming (enteric fermentation, animal wastes)(29%)
- Human: waste disposal sites (sewage, landfill, biomass burning) (28%)
NB: anthropogenic release is currently estimated to be 2.5 times larger than natural release.
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