Natural methane fluctuations are primarily caused by variations in microbial activity in wetlands, changes in wetland extent, and environmental factors such as temperature and precipitation. Key natural sources include wetlands, thawing permafrost, ecosystem fires, and geological emissions. Main causes of natural methane fluctuations:

• Wetlands: Microbial decomposition of organic matter in wetlands produces methane. Changes in wetland area and productivity strongly influence methane emissions. Wetland methane emissions are closely tied to net primary productivity (NPP), which itself depends on atmospheric CO2 levels, temperature, and rainfall patterns. As wetlands expand or contract, especially shifting toward higher latitudes with warming, methane emissions fluctuate accordingly

• Temperature and precipitation: Warmer temperatures and increased rainfall enhance microbial activity in wetlands, increasing methane production. For example, tropical wetlands have seen increased methane emissions due to wetter and warmer conditions over recent decades. Similarly, anomalously warm years and heavy rains can enlarge wetlands, boosting methane release

• Permafrost thawing: In Arctic regions, warming can thaw permafrost, releasing methane previously trapped in frozen soils. This can cause episodic spikes in methane emissions, although such spikes may not be persistent year-to-year

• Other natural sources: Ecosystem fires, decay of organic matter, seeps from oceans and freshwater lakes, and geological sources also contribute to natural methane emissions, though wetlands dominate the natural budget

• Atmospheric chemistry: Fluctuations in methane removal processes, such as changes in atmospheric oxidants (e.g., hydroxyl radicals), can indirectly affect methane concentrations

In summary, natural methane fluctuations arise mainly from dynamic wetland ecosystems influenced by climate variables like temperature and precipitation, as well as permafrost thaw and other natural processes. These fluctuations can be amplified by climate change, creating feedback loops that may increase methane emissions further