New ice core data provides insight into climate ‘tipping points’ during the last Ice Age

Oregon State University

CORVALLIS, Ore. – A changing climate triggers a sudden shift in ocean circulation, creating weather havoc and plunging Earth into an abrupt new Ice Age.

It sounds like the basis for a Hollywood blockbuster - the 2004 science fiction disaster film “The Day After Tomorrow,” has similar plot lines – but it’s actually a scenario that played out multiple times during the last Ice Age, which ended more than 11,000 years ago.

Just published research from multiple ice cores collected across Greenland with data spanning up to 120,000 years provides new understanding of these abrupt events, how they unfold and what that might mean for the future.

The events, known as Dansgaard-Oeschger events, represent “tipping points” in Earth’s climate – situations in which the climate crosses a threshold that leads to sudden and large-scale change, said the study’s lead author, Christo Buizert, an associate professor in the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University.

“It is really important to understand such tipping points in the climate, because they may result in catastrophic and irreversible change,” he said.

The findings were just published in the Proceedings of the National Academy of Sciences.

The Dansgaard-Oeschger cycle, which occurred more than 25 times during the last Ice Age, according to previous research, is caused by rapid on-off switching of the Atlantic Meridional Overturning Circulation, or AMOC, which circulates water throughout the Atlantic Ocean. The powerful Gulf Stream, which carries warm tropical waters to the North Atlantic, is part of the AMOC.

“The AMOC is fundamentally unstable, and when it collapses, big things happen across the globe. There is significant cooling in Europe and around the North Atlantic, and the Indian and Asian monsoons fail,” Buizert said. “That instability was frequent during the last Ice Age. It is cause for concern for the future because climate models suggest the AMOC will likely weaken again under global warming, potentially impacting billions of people.”

Buizert is a paleoclimatologist who uses ice cores to reconstruct and understand past climate change. Scientists drill and collect ice cores in Greenland and Antarctica to analyze the water, dust and tiny air bubbles that have been trapped in the ice over time. Data from ice cores provides important records of Earth’s atmospheric changes over hundreds of thousands of years and have served as pillars for scientists’ understanding of past climate events.

Buizert and his colleague analyzed ice cores from across Greenland, including cores from south and coastal east Greenland that had not previously been studied in detail, to better understand the climate impact of Dansgaard-Oeschger events across the continent.

The new data, coupled with new climate modeling, suggests interactions between the AMOC and wintertime sea ice play a key role in the Dansgaard-Oeschger events. Scientists previously thought sea ice from the Nordic Seas north of Iceland was involved in these events, but the researchers’ new analysis suggests that winter sea ice would have extended much farther south, to 40 degrees latitude. This means the sea ice would have reached modern day France and New York City, where the action also took place in the film, “The Day After Tomorrow.”

“The model shows that the Nordic Seas alone wouldn’t be big enough to drive a climate change event of this size,” Buizert said. “It just doesn’t pack enough of a punch.”

The AMOC has been well-behaved over the last 11,700 years, but current climate conditions and climate modeling suggest it will likely weaken again in the future, though for different reasons than occurred in the last Ice Age, Buizert said.

“We know the AMOC will weaken, but will it collapse? That is the big question. The weakening is likely gradual for the time being, but it could cross a tipping point and become a catalyst for abrupt climate change events like we saw in the past,” he said. “The climate does not behave in linear patterns; it can change quickly and irreversibly.”

The research was supported by the National Science Foundation and done in collaboration with scientists from five countries. Drilling of the Renland ice core in eastern Greenland was led by the University of Copenhagen, Denmark.

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2402637121 

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

The Greenland spatial fingerprint of Dansgaard–Oeschger events in observations and models

Article Publication Date

21-Oct-2024

 

A blueprint for mapping melting ice sheets

Stanford University

 

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In Svalbard, researchers launch a device with an ice-penetrating radar system built around the Open Radar Code Architecture (ORCA), an open-source tool that allows scientists to build radars more cheaply and efficiently. (Image credit: Eliza Dawson)

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Credit: (Image credit: Eliza Dawson)

Researchers in the Stanford Radio Glaciology lab use radio waves to understand rapidly changing ice sheets and their contributions to global sea-level rise. This technique has revealed groundwater beneath Greenland, the long-term impacts of extreme melt, a process that could accelerate ice sheet mass loss in Antarctica, the potential instability of an ice sheet that could raise sea levels by 10 feet, and more. 

Now, PhD students within the group have created an open-source tool that others can use to make ice-penetrating radar systems, core instruments in the field of glaciology. The Open Radar Code Architecture (ORCA) offers scientists a cheaper, easier, and more efficient way to build both airborne and ground-based radars, even if they lack a technical engineering background. Ice-penetrating radars can cost tens or hundreds of thousands of dollars, while the lowest-cost version of the team’s open-source radar costs only $1,500.

“We’re enabling groups to build exactly the right instrument for what they’re trying to do,” said PhD student Thomas Teisberg, who developed the system along with Anna Broome, PhD ’24. 

Whereas previous radar systems were built with specific hardware components specialized for each use case, the new model’s hardware is generic and more easily reconfigured depending on the task at hand. Broome likens the design to a kitchen mixer, with a variety of attachments available depending on what you’re planning to make. By standardizing the basic building blocks of what that radar looks like, Broome and Teisberg have also created a uniform format to store data so glaciologists can effectively reuse each other’s data.

“I think we’re going to see some really exciting and first-of-their kind experiments enabled by this system,” said Principal Investigator Dustin Schroeder, an associate professor of geophysics at the Stanford Doerr School of Sustainability. Teisberg and Broome recently co-authored a study along with Schroeder in IEEE Transactions on Geoscience and Remote Sensing that offers a blueprint for building the tool. 

Seeing beyond the ice

The ice sheets and glaciers atop Greenland and Antarctica are critically important, providing habitats to wildlife, storing more than half of the planet’s freshwater, and contributing to the evolution of the climate. They’re a major contributor to the sea-level rise that threatens the 680 million people who live in low-lying coastal zones – yet the uncertainty of projections may be underestimating that threat. Earth’s ice sheets represent the largest contribution to uncertainty in average sea-level rise by 2100, according to Intergovernmental Panel on Climate Change (IPCC) models.

In order to grasp current ice loss and make projections into the future, scientists need to understand the land underneath the ice and how it impacts flows and stability. “If you want to understand how ice is going to melt and change, you need to know what the bottom of the ice sheet looks like,” said Teisberg.

Building a toolkit

Currently, scientists use a wide range of radar instruments to gather data that is subsequently analyzed and interpreted to understand how glaciers and ice sheets work. For a scientist trying to break into the field, or for those without an engineering background, it can be challenging to figure out what radar system is best suited to an intended use case. The ORCA platform is built from software-defined radio – a type of hardware that is reconfigurable using software – democratizing the ability to design customized instruments. 

“If the community embraces this new tool, I think we’ll see a lot more scientists collecting their own radar data and re-using the innards of those radar systems to study really varied parts of the ice sheet that currently you would need multiple different types of radars to observe,” said Broome, who is now an R&D electrical engineer at Sandia National Laboratories.

Ice-penetrating radar is a foundational tool for glaciologists, but until now, most systems have been built by electrical engineers, not glaciologists, explained Robert Hawley, a physical glaciologist and professor of Earth sciences at Dartmouth College whose research group uses ice-penetrating radar and builds instrumentation for the frozen components of the Earth’s system. The learning curve for building hardware is very steep, he said. “By releasing their work as open-source software, Thomas and Anna have enabled a new generation of researchers to access and build ice-penetrating radars, which will spur a resurgence in this kind of research. This enables the scientists, asking the science questions, to get involved in a way that was not previously possible.”

Collecting better data

The idea for the open-source platform arose when Broome and Teisberg were separately developing plans for radar systems that map the land underneath ice sheets. 

“At some point we realized, wait a minute, we could team up and build the instruments on a common core, adapt them to our needs, and save a lot of work that way,” said Teisberg. 

Ice-penetrating radar acts like other radar: It sends out electromagnetic waves and records the timing of their reflections to determine an object’s distance. Ice-penetrating radar uses lower frequencies than most other radar systems and aims those waves straight down to penetrate through the ice and provide reflections off the ice surface, as well as the bedrock or sediment sitting underneath the ice.

While the tool is straightforward, flying a crewed aircraft in Greenland is no small feat – it costs a lot of money and requires a complicated set of logistics. “Our hope is that by standardizing the core of the radar, we can still allow people to build their customizations, and we can make it much easier for people to reuse data that’s been collected. By doing that, we can extract a lot more value out of every piece of data that gets collected,” Teisberg said.

The new study includes blueprints for building the two specific instruments that Broome and Teisberg engineered for their own PhD research. Teisberg is the first to admit that they have not built a new instrument. “We are standing on the shoulders of many, many people who’ve done a lot of incredible work in this field before. We’re just making an existing type of instrument much more accessible.” 

To test their prototypes, Broome and Teisberg traveled to Iceland, Svalbard, and most recently to Summit Station, the National Science Foundation-run research station at the top of the Greenland ice sheet. They confirmed their functionality by comparing results with previously acquired data from those areas – and they hope their research is just the beginning. Schroeder said the open-source tool is like a gift to the glaciology community.

“I would have loved if ORCA would have been around when I was a student,” Schroeder said. “I’m really excited about the opportunities it presents for students in my own group and for glaciology students around the world.”

Schroeder is also an associate professor of electrical engineering and a senior fellow at the Woods Institute for the Environment. Teisberg is a PhD candidate in electrical engineering in the School of Engineering. This research was supported by NASA, the NSF, NDSEG, and the Heising-Simons Foundation. Additional support was provided by the TomKat Center for Sustainable Energy, Stanford University Human-Centered Artificial Intelligence (HAI), and the Stanford Data Science industrial affiliates program. Stanford industrial affiliates programs are funded by membership fees from companies. View current members of Stanford Data Science.

In Svalbard, Thomas Teisberg reviews a flight plan for the Peregrine UAV before launch. (Image credit: Eliza Dawson)

Credit

(Image credit: Eliza Dawson)

Anna Broome pulling the radar/radiometer she built using ORCA behind a snowmobile near Summit Station in Greenland. (Image credit: Thomas Teisberg)

Researchers download data after a flight of the Peregrine UAV in Svalbard. The Peregrine system’s payload is a miniaturized ice-penetrating radar built around ORCA. (Image credit: Thomas Teisberg)

 

Credit

(Image credit: Thomas Teisberg)

Journal

IEEE Transactions on Geoscience and Remote Sensing

DOI

10.1109/TGRS.2024.3446368 

Article Title

Open Radar Code Architecture (ORCA): A Platform for Software-Defined Coherent Chirped Radar Systems

 

Rapidly increasing industrial activities in the Arctic

Sustainable development and conservation

University of Zurich

 

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Pan-Arctic light-emitting human activity map showing unlit areas versus lit areas with significantly increasing or decreasing light-emitting human activity from 1992 to 2013.

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Credit: Cengiz Akandil, University of Zurich; Natural Earth

The Arctic is threatened by strong climate change: the average temperature has risen by about 3°C since 1979 – almost four times faster than the global average. The region around the North Pole is home to some of the world’s most fragile ecosystems, and has experienced low anthropogenic disturbance for decades. Warming has increased the accessibility of land in the Arctic, encouraging industrial and urban development. Understanding where and what kind of human activities take place is key to ensuring sustainable development in the region – for both people and the environment. Until now, a comprehensive assessment of this part of the world has been lacking.

More than 5% of the Arctic show signs of human activity

An international research team led by Gabriela Schaepman-Strub from the Department of Evolutionary Biology and Environmental Studies at the University of Zurich (UZH) has now shed light on this question. Together with US colleagues from NASA and the University of Wisconsin-Madison, the UZH researchers used data of nighttime artificial light observed from satellites to quantify the hotspots and evolution of human activity across the Arctic from 1992 to 2013. “More than 800,000 km2 were affected by light pollution, corresponding to 5.1% of the 16.4 million km2 analyzed, with an annual increase of 4.8%,” says Schaepman-Strub. With the new, standardized approach the researchers were able to spatially assess human industrial activity across the Arctic, independent of economic data.

The European Arctic and the oil and gas extraction regions of Alaska, USA, and Russia were hotspots of human activity, with up to one-third of the land area illuminated. Compared to these regions, the Canadian Arctic was largely dark at night. “We found that, on average, only 15% of the lit area in the Arctic contained human settlements, which means that most of the artificial light is due to industrial activities rather than urban development. And this major source of light pollution is increasing in both area and intensity every year,” says first author Cengiz Akandil, a doctoral student in Schaepman-Strub’s team.

Effects on terrestrial ecosystems and regional sustainability

According to the researchers, these data provide an essential basis for future studies on the impact of industrial development on Arctic ecosystems. “In the vulnerable permafrost landscape and tundra ecosystem, even just repeated trampling by humans, and certainly tracks left by tundra vehicles, can have long-term environmental effects that extend well beyond the illuminated area detected by satellites,” says Akandil.

The negative impacts of industrial activities and light pollution are absolutely critical for the Arctic biodiversity. For example, artificial light at night reduces the ability of Arctic reindeer to adapt their eyes to the extreme blue color of winter twilight, which allows them to find food and escape predators. It also delays leaf coloration and breaking leaf buds, which is critical for the Arctic species where the growing season is limited. Furthermore, human activities foster the expansion of invasive species in the Arctic, and oil and gas extraction frequently lead to environmental pollution – as does the mining industry, which is also expanding.

Documenting industrial activity is crucial for sustainable development

The effects of rapid climate change in the Arctic require local communities to adapt quickly, and the industrial development might further increase the need for adaptation – and enhance the costs on society and the environment. The direct impacts that human activity has on Arctic ecosystems could exceed or at least exacerbate the effects of climate change in the coming decades, the researchers estimate. If the growth rate of industrial development between 1940–1990 is maintained, 50–80% of the Arctic may reach critical levels of anthropogenic disturbance by 2050.

“Our analyses on the spatial variability and hotspots of industrial development are critical to support monitoring and planning of industrial development in the Arctic. This new information may support Indigenous Peoples, governments and stakeholders to align their decision-making with the Sustainable Development Goals in the Arctic,” concludes Gabriela Schaepman-Strub.

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2322269121 

Method of Research

Data/statistical analysis

Subject of Research

Not applicable

Article Title

Artificial light at night reveals hotspots and rapid development of industrial activity in the Arctic

Article Publication Date

21-Oct-2024

 

Towards better solar cells: Exploring an anomalous phenomenon of electricity generation

Researchers explore the bulk photovoltaic effect in a promising material for next-generation solar harvesting technologies

Peer-Reviewed Publication

Shinshu University

 

image: 

In this study, researchers demonstrated that α-In2Se3 exhibits a peculiar way of generating electricity from light called the bulk photovoltaic effect. Based on their experimental results, α-In2Se3-based devices could achieve remarkable performance in solar cells, paving the way for reliable renewable energy generation to achieve carbon neutrality.

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Credit: zakzak 7 at Openverse ( https://openverse.org/image/46233968-b662-4fb5-bfcd-64d5c2795410)

The bulk photovoltaic (BPV) effect is an uncommon phenomenon that may enable certain materials to outperform the conventional p–n junctions used in solar cells. In a recent study, researchers from Japan have experimentally demonstrated the BPV effect in alpha-phase indium selenide (α-In2Se3) for the first time along the out-of-plane direction, validating previous theoretical predictions. The remarkable conversion efficiency recorded in their α-In2Se3 device signals a promising advancement for future solar cell technologies and photosensors.

A firm understanding of the photovoltaic effect, by which light can be converted into useful electrical energy, lies at the core of solar cell design and development. Today, most solar cells employ p–n junctions, leveraging the photovoltaic effect that occurs at the interface of different materials. However, such designs are constrained by the Shockley–Queisser limit, which puts a hard cap on their theoretical maximum solar conversion efficiency and imposes a tradeoff between the voltage and current that can be produced via the photovoltaic effect.

However, certain crystalline materials exhibit an intriguing phenomenon known as the bulk photovoltaic (BPV) effect. In materials lacking internal symmetry, electrons excited by light can move coherently in a specific direction instead of returning to their original positions. This results in what is known as “shift currents,” leading to the generation of the BPV effect. Although experts have predicted alpha-phase indium selenide (α-In2Se3) to be a possible candidate to demonstrate this phenomenon, it hasn’t yet been experimentally investigated.

To fill this knowledge gap, a research team from Japan led by Associate Professor Noriyuki Urakami from Shinshu University set out to explore the BPV effect in α-In2Se3. Their findings were published in Volume 125, Issue 7 of Applied Physics Letters on August 12, 2024 and made available online on August 14, 2024.

“This material has recently become a hot topic in the field of condensed matter physics, as it might be able to generate a shift current. Our study is the first to experimentally demonstrate this prediction,” shares Prof. Urakami.

First, the researchers produced a layered device composed of a thin α-In2Se3 layer sandwiched between two transparent graphite layers. These graphite layers served as electrodes and were connected to a voltage source and an ammeter to measure any generated currents upon light irradiation. Notably, the team employed this specific arrangement of layers because they focused on the shift currents occurring in the out-of-plane direction in the α-In2Se3 layer.

After testing with different external voltages and incident light of various frequencies, the researchers verified the existence of shift currents in the out-of-plane direction, confirming the abovementioned predictions. The BPV effect occurred throughout a wide range of light frequencies.

Most importantly, the researchers gauged the potential of the BPV effect in α-In2Se3 and compared it to that in other materials. “Our α-In2Se3 device demonstrated a quantum efficiency several orders of magnitude higher than other ferroelectric materials, and a comparable one to that of low-dimensional materials with enhanced electric polarization,” remarks Prof. Urakami. He further adds, “This discovery will guide material selection for the development of functional photovoltaic devices in the near future.”

The research team is hopeful that their efforts will eventually have a positive environmental impact by contributing to the field of renewable energy generation. “Our findings have the potential to further accelerate the spread of solar cells, one of the key technologies for environmental energy harvesting and a promising avenue towards a carbon neutral society,” concludes a hopeful Prof. Urakami.

We hope that this study paves the way for further studies to harness the BVP effect and vastly improve the performance of solar cells, as well as enhance the design of sensitive photodetectors.

 

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About Shinshu University

Shinshu University is a national university founded in 1949 and located nestling under the Japanese Alps in Nagano known for its stunning natural landscapes. Our motto, "Powered by Nature - strengthening our network with society and applying nature to create innovative solutions for a better tomorrow" reflects the mission of fostering promising creative professionals and deepening the collaborative relationship with local communities, which leads to our contribution to regional development by innovation in various fields. We’re working on providing solutions for building a sustainable society through interdisciplinary research fields: material science (carbon, fiber and composites), biomedical science (for intractable diseases and preventive medicine) and mountain science, and aiming to boost research and innovation capability through collaborative projects with distinguished researchers from the world. For more information visit https://www.shinshu-u.ac.jp/english/ or follow us on X (Twitter) @ShinshuUni for our latest news.

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Journal

Applied Physics Letters

DOI

10.1063/5.0222926 

Method of Research

Experimental study

Subject of Research

Not applicable

Article Title

Bulk photovoltaic effect of an alpha-phase indium selenide(α-In2Se3) crystal along the out-of-plane direction

 

Evolution in action: How ethnic Tibetan women thrive in thin oxygen at high altitudes

New study from Case Western Reserve University reveals link between oxygen delivery and reproductive success among women living on the high Tibetan Plateau

Case Western Reserve University

 

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View of a Tibetan village from the Himalayas. 

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Credit: Photo courtesy of James Yu

Breathing thin air at extreme altitudes presents a significant challenge—there’s simply less oxygen with every lungful. Yet, for more than 10,000 years, Tibetan women living on the high Tibetan Plateau have not only survived but thrived in that environment.

A new study led by Cynthia Beall, Distinguished University Professor Emerita at Case Western Reserve University, answers some of those questions. The new research, recently published in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS), reveals how the Tibetan women’s physiological traits enhance their ability to reproduce  in such an oxygen-scarce environment.

The findings, Beall said, not only underscore the remarkable resilience of Tibetan women but also provide valuable insights into the ways humans can adapt in extreme environments. Such research also offers clues about human development, how we might respond to future environmental challenges, and the pathobiology of people with illnesses associated with hypoxia at all altitudes.

“Understanding how populations like these adapt,” Beall said, “gives us a better grasp of the processes of human evolution.”

The study

Beall and her team research studied 417 Tibetan women age 46 to 86 who live between 12,000 and 14,000 feet above sea level in location in Upper Mustang, Nepal on the southern edge of the Tibetan Plateau.

They collected data on the women’s reproductive histories, physiological measurements, DNA samples and social factors. They wanted to understand how oxygen delivery traits in the face of high-altitude hypoxia (low levels of oxygen in the air and the blood) influence the number of live births—a key measure of evolutionary fitness.

Adaptation into thin air

They discovered that the women who had the most children had a unique set of blood and heart traits that helped their bodies deliver oxygen. Women reporting the most live births, had levels of hemoglobin, the molecule that carries oxygen, near the sample’s average, but their oxygen saturation was higher, allowing more efficient oxygen delivery to cells without increasing blood viscosity; the thicker the blood, the more strain on the heart.

“This is a case of ongoing natural selection,” said Beall, also the university’s Sarah Idell Pyle Professor of Anthropology. “Tibetan women have evolved in a way that balances the body’s oxygen needs without overworking the heart."

A window into human evolution

Beall’s interdisciplinary research team, which included longtime collaborators Brian Hoit and Kingman Strohl, from the Case Western Reserve School of Medicine, and other U.S. and international researchers, conducted fieldwork in 2019. The team worked closely with local communities in the Nepal Himalayas, hiring local women as research assistants and collaborating with community leaders.

One genetic trait they studied likely originated from the Denisovans who lived In Siberia about 50,000 years ago;  their descendants later migrated onto the Tibetan Plateau.  The trait is a variant of the EPAS1 gene that is unique to populations indigenous to the Tibetan Plateau and regulates hemoglobin concentration. Other traits, such as increased blood-flow to the lungs and wider heart ventricles, further enhanced oxygen delivery. These traits contributed to greater reproductive success, offering insight into how humans adapt to lifelong levels of low oxygen in the air and their bodies. 

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2403309121 

Method of Research

Randomized controlled/clinical trial

Subject of Research

People

Article Title

Higher oxygen content and transport characterize high-altitude ethnic Tibetan women with the highest lifetime reproductive success

Article Publication Date

21-Oct-2024

COW FARTS 💩

Microbes drove methane growth between 2020 and 2022, not fossil fuels, study shows

University of Colorado at Boulder

Microbes in the environment, not fossil fuels, have been driving the recent surge in methane emissions globally, according to a new, detailed analysis published Oct 21 in the Proceedings of the National Academy of Sciences by CU Boulder researchers and collaborators.

“Understanding where the methane is coming from helps us guide effective mitigation strategies,” said Sylvia Michel, a senior research assistant at the Institute of Arctic and Alpine Research(INSTAAR) and a doctoral student in the Department of Atmospheric and Oceanic Sciences at CU Boulder. “We need to know more about those emissions to understand what kind of climate future to expect.”

Methane is a potent greenhouse gas responsible for about a third of the planet’s warming since industrialization. Although the atmosphere contains less methane than carbon dioxide, methane traps about 30 times more heat than carbon dioxide over a 100-year time frame, making it a critical target for addressing climate change. 

“Methane concentrations in the air have almost tripled since the 1700s,” said co-author Jianghanyang (Ben) Li, an assistant professor in the Department of Atmospheric and Oceanic Sciences and INSTAAR. 

But unlike CO2, which can stay in the atmosphere for thousands of years, methane degrades within a decade. As a result, addressing methane emissions can have an immediate and powerful impact in slowing the rate of warming, making it a “low-hanging fruit,” Li said.

While the finding suggests microbes have been emitting more methane than fossil fuels in recent years, reducing fossil fuel consumption remains key to addressing climate change, the team said. Cutting down food waste and consuming less red meat can also help lower one’s methane footprint.

ID the source

Previous research suggests fossil fuel production is responsible for about 30% of global methane emissions. 

But microbial sources—such as wetlands, cattle and landfills— are an even more significant source of methane, accounting for more than half of global emissions. Archaea, a type of microorganism living in soil and the guts of cows, produce methane as a byproduct of breaking down organic matter. 

Michel and Li have been working with Boulder’s Global Monitoring Laboratory (GML) at the National Oceanic and Atmospheric Administration (NOAA) over the past years. 

The lab receives air samples from 22 sites around the world every week or two. Researchers then isolate different components of the air—such as CO2 or methane—for analysis. By examining the types of carbon atoms, or isotopes, that the methane sample contains, Michel, Li and the team can identify its source. For example, methane from fossil fuels has more carbon-13 isotope than methane in the air, and methane from microbial sources contains even less carbon-13. The lab has been measuring isotopes of methane since 1998.

Scientists have observed a rapid increase in atmospheric methane levels since 2007, following a period of stabilization in the early 21st century. In 2020, NOAA reported the highest growth rate of methane since it began collecting data in 1983, and that record was shattered again in 2021.

At the same time, Michel noticed a surprising decrease in the carbon-13 isotope over the past 17 years. She and the team set out to understand what was driving it.

The culprit

Using computer simulations, Michel and her team modeled three different emissions scenarios to see which one would leave an isotopic signature similar to the one observed. 

They found that between 2020 and 2022, the drastic increase in atmospheric methane was driven almost entirely by microbial sources. Since 2007, scientists have observed microbes playing a significant role in methane emissions, but their contribution has surged to over 90% starting in 2020.

“Some prior studies have suggested that human activities, especially fossil fuels, were the primary source of methane growth in recent years,” said Xin (Lindsay) Lan, a scientist at the Cooperative Institute for Research in Environmental Sciences (CIRES) at CU Boulder and NOAA. She leads the reporting on NOAA’s global greenhouse gas trends at the GML. “These studies failed to look at the isotope profile of methane, which could lead to a different conclusion and an incomplete picture of global methane emissions.”

It remains unclear whether the increased microbial emissions came from natural sources like wetlands or human-driven sources, such as landfills and agriculture. The team plans to delve deeper to identify the exact source of methane.  

“In a warming world, it wouldn't be surprising if any of these sources emitted more methane,” said Michel, who explained that microbes, like humans, tend to have higher metabolism when it’s warm. “Consequently, more methane could stay in the atmosphere to accelerate global warming. So we need to address the climate crisis, and that really means addressing CO2 emissions.”

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Journal

Proceedings of the National Academy of Sciences

DOI

10.1073/pnas.2411212121 

Article Title

Rapid shift in methane carbon isotopes suggests microbial emissions drove record high atmospheric methane growth in 2020–2022

Article Publication Date

21-Oct-2024