Global emissions of methane, a potent greenhouse gas, have reached the highest levels on record, new studies released Tuesday said.
The primary sources of the methane are fossil fuels and agriculture, the research said.
"Emissions from cattle and other ruminants are almost as large as those from the fossil fuel industry for methane," Stanford University scientist Rob Jackson said in a statement. "People joke about burping cows without realizing how big the source really is."
The findings are outlined in two papers published in Earth System Science Data and Environmental Research Letters by researchers with the Global Carbon Project, a project led by Jackson.
Methane is also the main ingredient in natural gas and is the second-largest contributor to global warming, after carbon dioxide.
In fact, the colorless, odorless gas is 28 times more powerful than carbon dioxide at trapping heat over a 100-year span.
More than half of all methane emissions now come from human activities, according to the research. Annual methane emissions are up 9%, or 50 million tons per year, from the early 2000s, when methane concentrations in the atmosphere were relatively stable.
Jackson said that adding this much extra methane to the atmosphere since 2000 is like putting 350 million more cars on the world's roads or doubling the total emissions of Germany or France. "We still haven't turned the corner on methane," he said in the statement.
Between 2000 and 2017, levels of methane soared toward pathways that climate models suggest will lead to up to 4 degrees Celsius of warming before 2100.
"This is a dangerous temperature threshold at which scientists warn that natural disasters, including wildfires, droughts and floods, and social disruptions such as famines and mass migrations become almost commonplace," the Global Carbon Project said.
Around the world, methane emissions rose most in Africa and the Middle East; China; and South Asia and Oceania, which includes Australia and many Pacific islands.
The U.S. followed close behind, the research found, increasing methane emissions by 4.5 million tons, mainly due to more natural gas drilling, distribution and consumption.
"Natural gas use is rising quickly here in the U.S. and globally," Jackson said. "It's offsetting coal in the electricity sector and reducing carbon-dioxide emissions, but increasing methane emissions in that sector." The U.S. and Canada are also producing more natural gas.
"As a result, we're emitting more methane from oil and gas wells and leaky pipelines," said Jackson.
This article originally appeared on USA TODAY: Methane emissions soar to record levels worldwide