Methane emissions are at their highest level ever, with agriculture and fossil fuels the biggest drivers, according to new research.

Climate models suggest that continued increases in methane levels could see global temperatures increase by 3-4 degrees Celsius by 2100, researchers from the Global Carbon Project said in a statement published Wednesday.

Researchers looked at methane emissions from 2000 to 2017, the last year for which complete global data are available, and warn that the current path leads toward a "dangerous temperature threshold," according to the statement.

Both natural disasters, such as wildfires, floods and droughts, and social disruptions, including mass migrations and famines, would become "almost commonplace," it said.

Methane is 28 times more effective than carbon dioxide at trapping heat over 100 years, the team said, and human activity accounts for more than half of methane emissions.

Annual emissions of the greenhouse gas have risen by 9% since 2000, which has the same effect on warming as adding 350 million cars to our roads.

The team, led by Rob Jackson, a professor of Earth system science in Stanford University's School of Earth, Energy & Environmental Sciences, published two papers in the journals Earth System Science Data and Environmental Research Letters on Wednesday.

The research showed that cattle ranching is the main reason for increased methane levels.

"Emissions from cattle and other ruminants are almost as large as those from the fossil fuel industry for methane," Jackson said. "People joke about burping cows without realizing how big the source really is."

Agriculture as a whole produces two-thirds of total emissions, with rice cultivation and biomass burning also significant contributors, according to the researchers.

Fossil fuels account for most of the remaining third, and the two sources have contributed almost equally to the recent increases.

While carbon emissions fell significantly during the coronavirus lockdown, as manufacturing and transport activity fell off a cliff, that's not the case for methane, according to Jackson.

"We're still heating our homes and buildings, and agriculture keeps growing," he said.

Africa and the Middle East, China, and South Asia and Oceania saw the sharpest rises in methane emissions, with the US close behind.

In the US, the increase has been driven by increasing use of natural gas. This reduces CO2 emissions by offsetting the use of coal, but it releases more methane.

Europe is the only region where methane emissions have fallen, thanks in part in greater efficiency in agriculture and reduced emissions from chemical manufacturing.

"Policies and better management have reduced emissions from landfills, manure and other sources here in Europe. People are also eating less beef and more poultry and fish," said Marielle Saunois of the Université de Versailles Saint-Quentin in France, lead author of the paper in Earth System Science Data.

The biggest rises in emissions were seen in tropical and temperate regions.

Researchers say it is hard to work out where natural methane emissions are coming from, compared with human-driven emissions.

In order to reduce methane emissions we need to cut the use of fossil fuels and control emissions from leaky pipelines and wells, the researchers said, with Jackson optimistic that drones, satellites and aircraft monitoring wells will lead to major progress in the field in the next five years.

We also need to implement new ways of growing and eating food, the team said, for example by supplementing cattle feed with algae that can reduce the amount of methane burped out by cows.

On Tuesday, fast food chain Burger King announced a plan to improve its cows' diet by adding lemongrass to their feed.

This change in diet will reduce the cows' methane emissions by 33% a day, the company said.

text by Jack Guy, CNN