Pre-industrial rise in methane gas was a consequence of both human activities and natural causes, researchers of a new study found.
For decades now, scientists have debated about whether human activities or natural causes were to blame for the pre-industrial rise in methane gas. Now, through a new study, they finally have their answer. Both factors were to blame for this occurrence, rather than just one of them, according to a press release.
Although many papers in the past have concluded that humans might have caused a rise in greenhouse gases, this alone doesn't fully explain the rising levels of atmospheric methane during the past 5,000 years. Instead, it's very likely that human-caused methane was supplemented by environmental factors.
In order to determine methane levels in the past, the researchers examined ice cores from Polar regions. Gas bubbles containing ancient air trapped within the ice can be analyzed and correlated with chronological data. This can then tell scientists what the atmosphere was like over a series of decades. The researchers then used previous models that hypothesized reasons for the methane increase that began 5,000 years ago. They then compared these models to the ice core data.
They found that ice cores from Greenland had higher methane levels that those from Antarctica. This is because there is greater methane gas emission in the Northern hemisphere. The difference in methane levels, called the Inter-Polar Difference, though, did not change appreciably over time.
"If the methane increase was solely natural or solely anthropogenic, it likely would have tilted the Inter-Polar Difference out of its pattern of relative stability over time," said Logan Mitchell, one of the researchers, in the news release.
The findings reveal that it's likely that both the environment and humans played a role in the increasing methane levels during this time period.
"We think that both played a role," said Mitchell in a news release. "The increase in methane emissions during the late Holocene came primarily from the tropics, with some contribution from the extratropical Northern Hemisphere. Neither modeled natural emissions alone, nor hypothesized anthropogenic emissions alone, are able to account for the full increase in methane concentrations. Combined, however, they could account for the full increase."
