he Bakken, which spans North Dakota and Montana and extends into Canada, is pumping around 226,000 tonnes of fugitive ethane emissions into the atmosphere per annum, around 2% of the global total.

"Two percent might not sound like a lot, but the emissions we observed in this single region are 10 to 100 times larger than reported in inventories,” the report’s co-author and UM assistant professor of climate and space sciences and engineering Eric Kort said.

“They directly impact air quality across North America.

“And they're sufficient to explain much of the global shift in ethane concentrations."

Kort’s study, which was published in Geophysical Research Letters, solves a scientific mystery from 2010 when a mountaintop sensor in Europe registered an ethane uptick after levels had reduced between 1984 and 2009.

Scientists attributed its declining levels since the 1980s to less venting and flaring of gas from oil fields and less leakage from production and distribution systems, but the advent of fraccing and the North Dakota oil boom appears to have been responsible for the explosion in ethane readings.

Bakken oil production jumped by a factor of 3500 and its gas production by 180 times between 2005 and 2014, although it has recently plateaued since the oil price collapsed.

To gather their data, the researchers flew over the Bakken formation for two weeks in 2014 and measured the field's ethane emissions of 0.23 teragrams per year, or roughly 226,000t, effectively cancelling out half of the global decline rate.

Ethane emissions from other US fields, especially the Eagle Ford Shale in Texas, are likely to have contributed to emissions as well, the research team says.

The findings illustrate the key role of shale oil and gas production in rising ethane levels.

"These findings not only solve an atmospheric mystery – where that extra ethane was coming from–they also help us understand how regional activities sometimes have global impacts," co-author Colm Sweeney, a scientist with the Cooperative Institute for Research in Environmental Sciences at the University of Colorado Boulder, said.

"We did not expect a single oil field to affect global levels of this gas."

Ethane, which is the second most abundant atmospheric hydrocarbon can damage air quality and impact climate and can combine with sunlight and other molecules in the atmosphere to form ozone, which at the surface can cause respiratory problems, eye irritation and other ailments and damage crops.

Exposure over time can be harmful.

Worse, it is the third-largest contributor to human-caused global warming after carbon dioxide and methane.