Global annual methane emissions and sinks 2008-2017, by source

Based on estimated annual averages from 2008 to 2017, human-made and natural fluxes in emissions release between 576 and 737 megatons (million tons) of methane into the atmosphere each year, while chemical reactions in the atmosphere and sequestration into the soil absorbs between 556 and 625 megatons of methane, meaning that there is a surplus of methane emitted into our atmosphere each year. Precise figures for this surplus are difficult to quantify, as both the bottom-up and top-down estimates for each source are the mid-values of estimate ranges, however the Global Carbon Project gave a bottom-up estimate of over 100 megatons per year, and a top down estimate of around 13 megatons per year.

Comparison with carbon dioxide

While the figures for methane are well below the volume of excess carbon dioxide (CO₂) released into the atmosphere, - around 5,100 megatons (or 5.1 gigatons) per year in the 2010s - methane has a much higher impact on climate change when both quantities are the same. Based on their global warming potential (GWP), which assesses greenhouses gases on their ability to trap heat in the atmosphere compared to CO₂, methane has a GWP of 70-80 over a 20 year period, meaning that one ton of methane in the atmosphere would trap the same amount of heat as 70-80 tons of CO₂ over a 20 year period.
Methane's GWP falls to around 25-30 over a 100 year period, due to variations in the length of time each greenhouse remains in the atmosphere, however the immediacy of the threat posed by climate change means that methane emissions should not be ignored. For example, if the upper estimate of 100 megatons of surplus methane is correct, then this has the potential to trap the same amount of heat as 80,000 megatons of CO₂ over a 20 year period, which is over 15 times higher than the actual figure.