Roughly two-thirds of all emissions of atmospheric methane — a highly potent greenhouse gas that is warming planet Earth — come from microbes that live in oxygen-free environments like wetlands, rice fields, landfills and the guts of cows.
Tracking atmospheric methane to its specific sources and quantifying their importance remains a challenge, however. Scientists are pretty good at tracing the sources of the main greenhouse gas, carbon dioxide, to focus on mitigating these emissions. But to trace methane’s origins, scientists often have to measure the isotopic composition of methane’s component atoms, carbon and hydrogen, to use as a fingerprint of various environmental sources.
A new paper by researchers at the UC Berkeley, reveals how the activity of one of the main microbial enzymes involved in producing methane affects this isotope composition and complicates efforts to pinpoint environmental sources. The finding could change how scientists calculate the contributions of different environmental sources to Earth’s total methane budget and lead to a more accurate picture of where exactly atmospheric methane is coming from.
“When we integrate all the sources and sinks of carbon dioxide into the atmosphere, we kind of get the number that we’re expecting from direct measurement in the atmosphere. But for methane, large uncertainties exist — within tens of percents for some sources — that challenge our ability to precisely quantify the relative importance and changes in time of the sources,” said UC Berkeley postdoctoral fellow Jonathan Gropp, who is first author of the paper. “To quantify the actual sources of methane, you need to really understand the isotopic processes involved in producing the methane.”
Gropp teamed up with a molecular biologist and a geochemist at UC Berkeley to, for the first time, employ CRISPR to manipulate the activity of this key enzyme to reveal how methane-producing microbes — methanogens — interact with their food supply to produce methane.