"We should be more concerned about methane released from human activities".
Earlier estimates were based on intermittent, bottom-up monitoring of oil and gas companies and comparisons with geological evidence from the end of the Pleistocene epoch, about 11,600 years ago.
Researchers at the University of Rochester in NY studied methane emissions from a period in Earth's history which bears many similarities to our current climate, examining ice cores taken from the last period of deglaciation some 8,000 to 15,000 years ago.
Researchers at the University of Rochester drilled and collected ice cores from Taylor Glacier in Antarctica.
Even so, Petrenko says, "anthropogenic methane emissions now are larger than wetland emissions by a factor of about two, and our data shows we don't need to be as concerned about large methane releases from large carbon reservoirs in response to future warming; we should be more concerned about methane released from human activities".
In the case of methane hydrates, if the methane is released in the deep ocean, most of it is dissolved and oxidized by ocean microbes before it ever reaches the atmosphere. Unlike CO2 (which ranks first), methane breaks down quickly - nine years on average, while CO2 can last for up to a century.
Accidents are also underreported.
But methane - the main component in natural gas and an even more effective heat-trapping gas - is a close second.
Fracking also appears to have worsened the problem.
By drilling and collecting ice cores in Greenland, Petrenko and his colleagues were able to use this isotope as a sort of time capsule for past atmospheres, ranging from roughly 1750 to 2013.
Growing calls for tighter controls will be strengthened by the new study. Because both types lack carbon-14, the scientists compared levels of carbon-14-depleted methane from the 1870s with levels from when the fossil fuel era was in full swing-in the decades leading up to the 1940s. The gas can arise from many sources, such as the fertilizer industry, agriculture, fossil fuels and the production of oil and gas, and new analysis from an worldwide team of researchers indicates we have been emitting far more than we thought.
This missing chunk could be part of the reason why we are now underestimating methane emissions so much.
"This indicates that the fossil fuel sector has a much more polluting impact beyond being responsible for the overwhelming majority of carbon dioxide emissions. This is worrying and overall bad news", said Dr Joeri Rogelj, a climate change lecturer at the Grantham Institute.
However, the good news is that methane leaves the atmosphere far more rapidly than carbon dioxide. But would this methane actually make it to the atmosphere? "This allows us to set climate policy priorities right". Researchers distinguish between the two by looking at the nature of the carbon isotopes this molecule contains - carbon-14 for fossil methane (which was locked in fossil fuel deposits) and "regular" carbon-13 for biological methane.
The data also shows that methane emissions from wetlands increased in response to climate change during the last deglaciation, and it is likely wetland emissions will increase as the world continues to warm today. "Add to that all the carbon dioxide that is then emitted when the fossil fuels are burned, and you need look no further for the seat of the climate emergency fire".