Final answer:
Methane is currently increasing at the fastest rate among greenhouse gases, partly due to activities such as the burning of fossil fuels and melting of clathrates. Carbon dioxide has the highest concentration overall, but the rate of increase for methane is greater at the moment.
Step-by-step explanation:
Fastest Increasing Greenhouse Gas
The concentration of methane (CH4) is currently increasing at the fastest rate among the key greenhouse gases. Despite being in smaller quantities compared to carbon dioxide, methane is approximately 21 times as effective per molecule at trapping heat within our atmosphere. About 64% of today's methane emissions are anthropogenic, meaning they are the result of human activities. The major sources of these emissions include the burning of fossil fuels, fermentation in the gastrointestinal tracts of ruminant animals like cattle, and the decomposition of organic matter in landfills.
It is important to note that while carbon dioxide (CO₂) has the highest overall concentration and is a significant contributor to global warming, the rate of increase in atmospheric methane is currently higher. Methane levels have seen a dramatic rise, increasing 2.5 times since the pre-industrial era. This rapid increase is further fueled by the melting of clathrates due to rising ocean temperatures, adding to the existing emissions from agricultural production, waste management, and energy use.