Energy think tank Ember used satellite imagery to calculate methane emissions from a string of Australian coal mines.

These mines in 2020 belched 40 percent more methane gas than was reported in Australian government estimates, Ember researchers said.

"Satellite estimates, including the one generated for this report, all point to the same finding -- there is a significant gap between reported emissions and satellite-based estimates," said Ember analyst Sarah Shannon.

Methane collects in underground coal deposits before leaking out when miners dig up the ground.

Coal mines are a major global source of methane emissions, according to the International Energy Agency.

But scientists have highlighted significant discrepancies between global greenhouse gas estimates and what is actually emitted.

"Given methane's high global warming potential, improving reporting is essential for identifying and implementing effective mitigation strategies," Shannon said.

Australia has in recent years tried to overhaul how it calculates methane emissions to get a more accurate picture.

"Australia's coal mine methane emissions remain under a cloud of international scrutiny," said Ember climate adviser Christopher Wright.

"These findings highlight that if we don't improve reporting, not only could our own emissions accounting be inaccurate, but our international customers can't know for certain what the scale of emissions lie embedded in their supply chains."

Atmospheric concentrations of methane have doubled in 200 years, according to NASA, driving up to 30 percent of global temperature rise.

While far less abundant in the atmosphere than carbon dioxide, methane is about 80 times more potent over a 20-year timescale at warming the planet.