Ice Cores Indicate Even Higher Methane Emissions Than Previously Believed

Ice Cores Indicate Even Higher Methane Emissions Than Previously Believed
Vasilii Petrenko loading an ice core into the melting chamber for extraction of trapped ancient air.
(Xavier Fain/U. Rochester)

Humans are probably contributing more methane to the atmosphere through fossil fuel use and extraction than scientists previously believed, report researchers.

They also find that the risk that warming will trigger methane release from large natural reservoirs of ancient carbon seems to be low.

In 2011 a team of researchers led by Vasilii Petrenko, an assistant professor of earth and environmental sciences at the University of Rochester, spent seven weeks in Antarctica collecting and studying 2,000-pound samples of glacial ice cores that date back nearly 12,000 years.

The ancient air trapped within the ice revealed surprising new data about methane that may help inform policymakers as they consider ways to reduce global warming.

“…anthropogenic (human-made) fossil fuel methane emissions are even larger than previously thought…”

The researchers report their findings in Nature.

“Our results are suggesting that anthropogenic (human-made) fossil fuel methane emissions are even larger than previously thought,” Petrenko says. “This means we have even more leverage to fight global warming by curbing methane emissions from our fossil fuel use.”

Today’s atmosphere contains methane that is emitted naturally—from wetlands, wildfires, or ocean and land seeps—and methane emitted from human activities like fossil fuel extraction and use, raising livestock, and generating landfills, with human-emitted methane accounting for 60 percent or more of the total.

Scientists are able to accurately measure the total methane level in the atmosphere and how this has changed over the last few decades.

The challenge? Breaking down this total into the specific sources.

“We know rather little about how much methane comes from different sources and how these have been changing in response to industrial and agricultural activities or because of climate events like droughts,” says Hinrich Schaefer, an atmospheric scientist at the National Institute of Water and Atmospheric Research (NIWA) in New Zealand, where a key part of the sample processing took place.

“That makes it hard to understand which sources we should target specifically to reduce methane levels,” says Schaefer.

Scientists can use measurements of different isotopes of methane (methane molecules with atoms of slightly different mass) to fingerprint some of the sources. But even this approach doesn’t always work because the isotope “signatures” of some sources can be very similar.

For instance, fossil methane is methane emitted from ancient hydrocarbon deposits, typically found at sites rich in fossil fuels. Fossil methane that leaks naturally from these sites—”geologic methane”—has an isotope signature that is identical to fossil methane emitted when humans drill gas wells.

Separating the natural and anthropogenic sources and estimating how much humans emit has therefore proven difficult.

In order to better understand the natural and anthropogenic components of fossil methane, Petrenko and his team turned to the past.

Petrenko’s lab is dedicated to understanding how both natural and human-made greenhouse gases respond to climate change. They analyze how past climate changes have affected greenhouse gases over time and the ways in which these gases might respond to future warming temperatures.

In this case, Petrenko and collaborators, studied past atmospheric records using ice cores extracted from Taylor Glacier in Antarctica. These cores date back nearly 12,000 years.

Every year that it snows in Antarctica, the current snow layer weighs on the previous layer, compacting over hundreds or thousands of years to eventually form layers of ice. These ice layers contain air bubbles, which are like tiny time capsules; using vacuum pumps and melting chambers, researchers are able to extract the ancient air contained within these bubbles and study the chemical compositions of the ancient atmosphere.

“Going back before any anthropogenic activities—before the Industrial Revolution—simplifies the picture…”

Humans did not begin using fossil fuels as a primary energy source until the Industrial Revolution in the 18th century. Because of this, 12,000-year-old ice cores contain no fossil methane originating from human activities; fossil methane levels are based solely on methane emitted from natural sources.

Natural geologic methane emissions of the past are thought to be comparable to natural emissions today, so studying ice cores allows researchers to very accurately measure these levels, separate from their anthropogenic counterparts.

“Going back before any anthropogenic activities—before the Industrial Revolution—simplifies the picture and allows us to estimate natural geologic sources very accurately,” Petrenko says.

The natural geologic methane levels the research team measured were three to four times lower than previously estimated numbers. If the natural geologic methane emissions are lower than expected, the anthropogenic fossil methane emissions must be higher than expected—Petrenko estimates by 25 percent or more.

The study also suggests that the risk of methane release from natural ancient carbon reservoirs is lower than previously thought. Scientists have raised the possibility that global warming could release methane from very large ancient carbon reservoirs such as permafrost and gas hydrates—ice-like forms of methane in the sediments at the bottom of the ocean. These become less stable as temperatures increase.

If climate change from burning fossil fuels were to trigger large emissions of methane to the atmosphere from these old carbon reservoirs, this would lead to even more warming.

“The ancient air samples reveal that these kinds of scenarios regarding natural methane emissions are not as important to take into account for future planning,” Petrenko says.

“In contrast, anthropogenic fossil fuel emissions seem to be even larger than we previously thought so reducing these levels has more leverage to mitigate global warming,” he says.

The National Science Foundation supported the research.

Source: University of Rochester

Related Books:

enafarzh-CNzh-TWnltlfrdehiiditjakomsfaptruesswsvthtrurvi

LATEST VIDEOS

Blue Ocean Event : Game Over?
by Just Have a Think
A Blue Ocean Event, or Ice-Free Arctic, is the source of almost fever pitch speculation in the climate science world.…
Climate Change - The Facts by Sir David Attenborough
by David Attenborough, BBC
After one of the hottest years on record, Sir David Attenborough looks at the science of climate change and potential…
Why it’s time to think about human extinction
by Kerwin Rae
After listening to this ep with Dr David Suzuki, you’ll never be the same again. The environmentalist, activist,…
Record Temperatures 20-25C Above Norm in far North
by Paul Beckwith
The Northwest Territories of Canada had March temperatures above 20C for the first time (hit 21.6C or 71F); breaking…
Why New CO₂ Capture Technology Is Not The Magic Bullet Against Climate Change
Why New CO₂ Capture Technology Is Not The Magic Bullet Against Climate Change
by Chris Hawes
According to a recent major UN report, if we are to limit temperature rise to 1.5 °C and prevent the most catastrophic…
Why Climate Change Will Dull Autumn Leaf Displays
Why Climate Change Will Dull Autumn Leaf Displays
by Matthew Brookhouse
Every autumn we are treated to one of nature’s finest seasonal annual transitions: leaf colour change and fall.
Climate denial isn’t stopping climate action.
by David Wallace-Wells
Climate change denial draws headlines. But is it actually an obstacle to climate action? A great majority of Americans…
Energy Storage: How to store renewable energy?
by Total
Under your bed, in the attic even on your mobile phone, it seems there's never enough storage. It turns out it's also…

LATEST ARTICLES

Crops at risk from changing climate
Crops at risk from changing climate
by Tim Radford
Global warming could bring yet more challenges to a hungry world. New studies have identified precise ways in which a…
Seeing The Planet Break Down In Climate Crisis Is Depressing – How To Turn Your Pain Into Action
Seeing The Planet In Climate Crisis Is Depressing – Turn Your Pain Into Action
by Cameron Brick
Environmentalism can feel like a drag. People trying to reduce their environmental impact often feel stressed and…
Global Inequality Is 25% Higher Than It Would Have Been In A Climate-stable World
by Nicholas Beuret
Those least responsible for global warming will suffer the most. Poorer countries – those that have contributed far…
Jason Kenney's Victory Means We'll All Pay The Price For Fossil Fuel Emissions
Jason Kenney's Victory In Alberta Means We'll All Pay The Price For Fossil Fuel Emissions
by D.T. Cochrane
Jason Kenney has led the United Conservative Party to victory in Alberta. There were manyobjectionablecomponents to the…
How Can Trees Really Cool Our Cities Down?
How Can Trees Really Cool Our Cities Down?
by Roland Ennos, University of Hull
In cities around the world, trees are often planted to help control temperatures and mitigate the effects of the “urban…
Beto O’Rourke Releases $5 Trillion Climate Change Proposal
Beto O’Rourke Releases $5 Trillion Climate Change Proposal
by Global Warming & Climate Change
But Varshini Prakash, executive director of the Sunrise Movement, a youth-led activist group that has advocated for the…
Should The Sahara Desert Be Turned Into A Huge Solar Farm?
Should The Sahara Desert Be Turned Into A Huge Solar Farm?
by Amin Al-Habaibeh
Whenever I visit the Sahara I am struck by how sunny and hot it is and how clear the sky can be.
How Retreating From The Sea Level Rise Will Affect Our Health?
How Retreating From The Sea Level Rise Will Affect Our Health?
by Jackson Holtz
Managed retreat in the face of sea level rise will be a mixed bag, researchers predict.