Short answers, pulled from the story.
By 2019, global atmospheric methane concentration reached 1,866 parts per billion (ppb), up from 722 ppb in pre-industrial times around 1750. That is an increase of approximately 160 percent and the highest level in at least 800,000 years. As of 2022, the average global concentration had risen further to 1,911.8 ppb.
Methane has a global warming potential 84 times greater than CO2 over a 20-year time frame. Over a 100-year time frame that figure drops to approximately 28 times greater than CO2, because methane breaks down faster than carbon dioxide does.
The main sources are microbial methanogenesis in aquatic ecosystems, ruminant animals, fossil fuels, and agricultural and waste processes such as landfills and manure management. Thawing Arctic permafrost also releases methane. All known major sources are located near the Earth's surface.
About 90 percent of atmospheric methane is destroyed by hydroxyl radicals (OH) in the troposphere through a chemical oxidation process that produces water vapor and carbon dioxide. Methanotrophic bacteria in soils and underwater sediments provide a second significant natural sink.
Researchers analyze gas bubbles trapped in Antarctic ice cores. From 1996 to 2004, the European Project for Ice Coring in Antarctica (EPICA) drilled and studied cores that allowed scientists to reconstruct greenhouse gas concentrations across the past 800,000 years.
Cavity ring-down spectroscopy became the most widely used infrared absorption technique for detecting methane by 2011. It is a form of laser absorption spectroscopy that can determine mole fraction to the order of parts per trillion.