It’s possible that I shall make an ass of myself. But in that case one can always get out of it with a little dialectic. I have, of course, so worded my proposition as to be right either way (K.Marx, Letter to F.Engels on the Indian Mutiny)
Tuesday, October 03, 2023
Improving air quality forecasting with daily update of emission inventory
In the realm of air quality forecasting, the precision of predictions largely hinges on the accuracy of emission inventory data. Traditional methods, which often update only once a year or less, face challenges in keeping pace with the dynamic nature of air pollutant emissions. This issue is particularly significant in China, where rapid changes in atmospheric pollutants demand a more agile approach.
Addressing this challenge, a recent study by the Institute of Atmospheric Physics, published in Environmental Science & Technology Letters and featured as a supplementary cover of the journal, has proposed an innovative emission update scheme tailored for air quality forecasting.
According to the first author Dr. Huangjian Wu, the strength in the new approach lies in that, in contrast to conventional methodologies, the new approach significantly reduces computational demands by an impressive 84%, making ensemble-based emission inversion cost-effective and practical for operational air quality forecasting.
Co-author Prof. Xiao Tang explained the essence of the approach, "Our methodology builds upon the ChemDAS data assimilation system and takes a significant step forward by decoupling ensemble simulations and forecasts required for emission inversion. This enables the daily estimation of emissions for major pollutants in urban areas."
This is echoed by Dr. Lei Kong, another contributor to the study, "Our technique estimates emissions for key pollutants like CO, SO2, NOx, VOCs, and PM2.5 and PM10 precursors by assimilating observed concentrations of CO, SO2, NO2, O3, PM2.5, and PM10, respectively."
The innovative method has already been successfully implemented at the China National Environmental Monitoring Centre (CNEMC), where it facilitates online inversion and updates of emission inventories for operational forecasting. "Our approach not only enhances forecast accuracy but also enables timely assessments of changes in atmospheric pollutant emissions," emphasized Prof. Zifa Wang, the corresponding author of the study.
In testing conducted between January and February 2022, the new method led to a notable 7.1% reduction in root mean square errors in 7-day PM2.5 forecasts and significantly improved predictions for pollutants like O3. Moreover, the updated emission data revealed significant reductions in nitrogen oxide emissions during the 2022 Beijing Winter Olympics, with Beijing experiencing a 53.5% reduction, Zhangjiakou a 42.7% reduction, and Hebei Province a 48.6% reduction.
This approach could advance air quality forecasting by providing timely, accurate, and cost-effective emission updates, contributing to the goal of healthier air for all.
More information: Huangjian Wu et al, Air Quality Forecasting with Inversely Updated Emissions for China, Environmental Science & Technology Letters (2023). DOI: 10.1021/acs.estlett.3c00266
by Ben Langford, James Ryalls and Robbie Girling, The Conversation
Honeybee (Apis mellifera) landing on a milk thistle flower (Silybum marianum). Credit: Fir0002/Flagstaffotos/ Wikipedia/GFDL v1.2
Whether you love them or loathe them, we all depend on bugs. Insects help to pollinate three-quarters of the world's crop varieties, making them a treasured resource.
But we're making the lives of insects tough—and not just by swatting them away with a newspaper. Insect populations worldwide are in sharp decline as they battle against climate change, habitat loss and pesticides.
Now, we can add air pollution to the list of threats. Our research from 2022 revealed that when exposed to two common air pollutants at concentrations within EU air quality limits, the visits of pollinating insects to flowers plummeted by as much as 90%.
Over a span of two years, we artificially elevated the levels of either ozone or diesel exhaust fumes around plots of flowering black mustard plants, all within fields of non-flowering wheat. We carefully monitored and controlled the release of pollutants using rings constructed around each plot.
This method allowed us to monitor the number of pollinating insects visiting the flowers in polluted plots and draw comparisons with plots devoid of pollutants.
We were surprised by what we found. In the rings where we released ozone or diesel exhaust fumes, the number of pollinating insects decreased by 70% and overall pollination success rates decreased by up to 31%.
It wasn't just bees and butterflies that were affected. Ground-dwelling insects suffered too, with exposure to these pollutants causing their numbers to decrease by as much as 36%.
Like Pavlov’s dogs, bees can be trained to respond to a dinner bell – or in their case, the scent of a flower.
Why air pollution makes life so hard
Many insects rely on their sense of smell to locate flowers. When they feed on nectar, they quickly connect the flower's scent with its sugary reward. Consequently, when they come across the same scent later on, they track its trail in pursuit of another tasty treat.
Thus, flowers serve a dual purpose. They are not just pretty to look at but also function as beacons that release a specific blend of fragrant chemicals designed to attract pollinators.
But these signals are under threat. Air pollutants like ozone are highly reactive and can degrade the signals by destroying the chemicals that make up a flower's scent.
In our more recent research, we simulated a floral scent in a 20-meter long wind tunnel and then mapped out how the levels of each of the chemicals that made up the scent changed in response to increasing ozone pollution. We found that ozone quickly ate away at the edges of the plume, reducing both its width and length.
Essentially, the chemical signal could travel only a shorter distance, which limited the number of insects it could reach.
Adding ozone also changes the smell of each of the chemicals that make up a flower's scent. By observing these changes in a wind tunnel, we could measure the speed at which these chemical changes occur.
Some chemicals degraded within seconds, whereas others were not affected at all. How far away you are from the scent's source appears to change how the scent smells.
Pavlov's Bees
To understand how changes to the floral scent might affect pollinators, we taught honeybees to recognize the same floral scent that we released into the wind tunnel. Much like Pavlov's dogs drooling at the sound of a dinner bell, bees stick out their proboscis (tube-like tongue) when they sniff an odor they have learned to associate with a sugary reward. This allowed us to see how many bees could still recognize the floral scent once it had been exposed to ozone pollution.
We first tested the honeybees with scent blends replicating those observed at the plume center when ozone levels were elevated. At a distance of six meters from the flower, 52% of bees recognized the scent. This fell to only 38% at a distance of 12 meters.
We then tested the response of honeybees to the more degraded plume edges. Only 32% of the bees responded at six meters, falling to just 10% at 12 meters.
These results help to explain the significant decline in the number and diversity of insect visits and pollination rates observed in our field trials. Put simply, ozone pollution limits the reach of chemical signals and changes their meaning, leaving insects confused.
But this is unlikely to be the full story. Although we replicated the effects of ozone pollution on floral scents, we never exposed the bees directly to ozone. Separate research carried out in France suggests that direct exposure to ozone might also impair the ability of bees to detect floral scents.
The full extent to which air pollution is impacting the insects we all depend on is only just beginning to be revealed. So, the next time you lift your newspaper to swat a bug, take a second and ask yourself—don't they have it tough enough already?
Climate change has made extreme weather events more frequent and intense worldwide. Some examples of climate-related disasters in recent years include the serious flooding in Venice, Italy in 2019, the terrible heat waves and wildfires in Australia in 2020, and the widespread flooding in Central Europe in 2021.
Although our understanding of climate extremes and their impacts continues to improve, events that overwhelm the coping capacity of social and environmental systems often take us by surprise. This is partly because current climate and impact modeling efforts are very limited in their ability to model compound events, making it difficult to plan for appropriate ways to adapt.
The COST Action Understanding and modeling compound climate and weather events (DAMOCLES) has succeeded in changing this situation. The Action has raised awareness of the importance of compound events and their impacts across different scientific fields. A recent study based on work from COST Action DAMOCLES has been published in iScience.
It has also created a new community bringing together experts in climate science, climate impact research, hydrology, and statistics. Bart van den Hurk of Deltares Institute, NL, and the vice-Chair of the Action, talks about the successes and challenges of DAMOCLES.
What are compound events?
Many major hydrometeorological disasters are often the result of compound events. These extreme events have a complex structure because they are caused by several factors or have multiple effects. For example, a coastal flood may become extreme due to a combination of a strong storm surge and heavy rainfall in the coastal area. A better understanding of these events can improve early warning, help design more effective defense infrastructure, and provide valuable information about the risks people face.
High-impact compound events come in many forms, such as droughts, heat waves, wildfires, and air pollution, where interactions between temperature, humidity, and precipitation play an important role. In addition, interactions between extreme precipitation, river discharge, and storm surge link coastal storm processes with fluvial/pluvial and ocean dynamics. Clustering of major storm events resulting in spatial and/or temporal dependence, is another example.
A notable example of a compound event occurred in Portugal in October 2017. Wildfires ravaged nearly 200,000 hectares of land in just 24 hours, resulting in 50 deaths. Several compounding factors contributed to this disaster, including long-term vegetation stress, the influence of Hurricane Ophelia, which brought hot and dry air masses to the region, and human negligence related to agricultural practices.
Another example is Russia in 2010, where a lack of rainfall combined with an atmospheric blocking event over western Russia led to an exceptionally hot and dry summer. This, in turn, led to widespread wildfires and air pollution, resulting in over 50,000 deaths, and destroying a quarter of Russia's crops.
Practical applications of DAMOCLES
When DAMOCLES started, the idea of compound weather and climate events was new and not widely understood. Only a few specialists, mostly coastal hydrologists, had expert knowledge of the underlying principles. DAMOCLES has played a crucial role in creating a framework for defining and managing compound events. It has also focused on showing how this framework can be applied in practice.
Van den Hurk, the vice-Chair of DAMOCLES, shared his personal experience with a client who was faced with a flood caused by a combination of different flooding factors. The client wanted to ensure that their analysis of the event would provide accurate inputs for the associated quantitative risk assessment associated with it. By demonstrating the physical connection between the various drivers, DAMOCLES enabled the client to adjust the risk calculations. This adjustment helped the client make an informed decision to invest in flood infrastructure, albeit a costly investment.
DAMOCLES success and impact
The Action has been very successful in defining and analyzing compound weather and climate events and has created a new category of specialists in this field. It has achieved very high visibility in the research community. DAMOCLES has published highly influential research papers that are expected to shape our thinking about compound events for years to come.
DAMOCLES scientific results are a key reference for studying and assessing compound events and associated risks that pose the most serious challenges to modern society from ongoing climate changes.
Van den Hurk states, "One of the major achievements of DAMOCLES has been the development of a typology for categorizing compound events. This typology helped to structure the extreme diversity of different event types, leading to improved methods for understanding compound events. The original paper presenting the typology, titled 'A typology of compound weather and climate events' was published in Nature Reviews Earth & Environment in 2020. It has already been cited more than 400 times according to Google Scholar.
"The typology has been used as a basis for follow-up activities of DAMOCLES, to provide Guidelines for Studying Diverse Types of Compound Weather and Climate Events and to link compound event thinking to the disaster risk reduction cycle (Consideration of compound drivers and impacts in the disaster risk reduction cycle).
"Another excellent outcome has been the inclusion of compound events in The Intergovernmental Panel on Climate Change IPCC. As the preeminent authority on climate change, the IPCC synthesizes the latest knowledge in the field and serves diverse audiences including policy makers, NGOs, scientists, industry, and the general public.
"These scientific findings are, and will continue to be, a key reference for studying and assessing compound events and associated risks that pose the most serious challenges to modern society from ongoing climate changes," concludes Van den Hurk.
More information: Bart J.J.M. van den Hurk et al, Consideration of compound drivers and impacts in the disaster risk reduction cycle, iScience (2023). DOI: 10.1016/j.isci.2023.106030
European Pied Flycatcher in Sweden. Credit: Wikipedia
One result of climate change is that spring is arriving earlier. However, migratory birds are not keeping up with these developments and arrive too late for the peak in food availability when it is time for breeding. By getting the birds to fly a little further north, researchers in Lund, Sweden, and the Netherlands have observed that these birds can give their chicks a better start in life.
Global warming is causing problems for birds in Sweden and elsewhere. Warmer springs mean that caterpillars hatch, grow and pupate earlier compared with just a few decades ago. This has consequences for birds that cannot eat caterpillars that have entered the pupal stage.
Therefore, when the food supply runs out at an ever earlier time in the spring, more and more chicks starve during the breeding season. This is a big problem for migratory birds that spend winters in Africa, as they do not know how early spring arrives in Sweden. Could the problem be solved if the migratory birds simply came home and started breeding earlier?
"It seems that our non-migratory birds are doing this to a certain extent. But, of course, they are present and can feel how early spring will come. We thought that perhaps the migratory birds could fly further north until they find a place with suitable well-developed caterpillars," says Jan-Åke Nilsson, biology researcher at Lund University in Sweden.
To test this in practice, the researchers decided to help some pied flycatchers along the way. The research is published in the journal Nature Ecology & Evolution.
The biologists caught pied flycatchers that had arrived prior to breeding in the Netherlands. The birds were then driven during the night to Vombs Fure, an area of pine forest outside Lund in Skåne, where they were released. The peak of caterpillar availability in Skåne is about two weeks later than in the Netherlands—a distance of around 600 kilometers that a pied flycatcher could cover in just two nights.
"The birds that were given a lift from the Netherlands to Skåne synchronized very well with the food peak. As they started to breed about 10 days earlier the 'Swedish' pied flycatchers they had a dramatically better breeding success than the Swedish ones as well as a better success than the pied flycatchers that remained in the Netherlands," says Jan-Åke Nilsson.
In addition, it was shown that the chicks of the Dutch pied flycatchers that had received migration assistance did not stop in the Netherlands when they returned after their first spring migration. Instead, they continued on to the area of pine forest outside Lund where they were born.
Furthermore, they arrived earlier than the Swedish pied flycatchers and thereby had more well-fed chicks at Vombs Fure the year after the researchers gave the pied flycatchers a helping hand to find Skåne.
"The number of small birds, particularly migratory birds, has decreased drastically throughout Europe. By flying a little further north, these birds, at least in principle, could synchronize with their food resources and there is hope that robust populations of small birds can be maintained, even though springs are arriving ever earlier," concludes Jan-Åke Nilsson.
More information: Koosje P. Lamers et al, Adaptation to climate change through dispersal and inherited timing in an avian migrant, Nature Ecology & Evolution (2023). DOI: 10.1038/s41559-023-02191-w
Clothes that are produced quickly and just as quickly go out of style and into the trash bin can have dire effects on the environment, polluting the air with carbon and choking landfills with chemicals that can seep into the water supply.
A Penn State Smeal College of Business-led team of researchers found a new business model may address the issue of overconsumption without burdening companies operating within the fiercely competitive fashion industry.
The researchers found that consumers are willing to pay more money for clothes they can customize and keep the items longer. The findings, published in the Journal of Operations Management, suggest that clothing companies that adopt a mass customization model can remain profitable while decreasing the fashion industry's environmental impacts.
"What we were asking is: How do we find a way to provide product variety while not suffering significant cost on initial manufacturing expenses?" said corresponding author Dan Guide, Smeal Chaired Professor of Operations and Supply Chain Management. "The big idea is that we'd like for people to stop disposing of stuff as fast as they do."
Aydin Alptekinoglu, professor of operations and supply chain management and Robert G. Schwartz University Endowed Fellow in Business Administration, served as first author on the paper.
"We hypothesized and showed that providing customization to cater for individual consumer tastes but at a mass scale—the idea of mass customization applied to fashion—might help delay the eventual disposal," Alptekinoglu said. "In fact, we think mass customization can be the basis for a new business model in fashion that is more sustainable and more profitable."
According to Guide, fast fashion refers to how the fashion industry often produces clothes made of inexpensive, plastic-based synthetic materials called polymers. Because the clothes are cheap and tend to wear out quickly, consumers are more likely to throw them out and buy new instead of attempting to repair them. The clothes typically end up in landfills and the chemicals that make up these cheap polymers can infiltrate the water supply.
"The big problem with these artificial fibers is that they are a complex blend of polymers," Guide said. "They're really many different types of plastic, which we tend to do a lousy job of sorting, so these polymers become too complicated to recycle and the plastics can, for example, end up seeping into the water supply."
Recycling is often not an option either because the polymers are often too complex to efficiently recover, added Guide.
Making business sense
According to Guide, by proving people will pay more for their personalized clothes, businesses can compensate by selling fewer clothes for more money, rather than selling more units of disposable clothing for less money.
No business will adopt a practice that will hurt its ability to compete, or hurt their investors, said Guide.
"Our business school and, in particular, my supply chain department does a lot of work with companies," Guide said. "So, when we talk to managers and engineers, I would feel very comfortable going into those businesses and those plants and telling them this is a way that you can make money while still doing good. I love that message for companies."
According to the researchers, the solution is also practical because the technology currently exists to allow many people to personalize their products online. For example, customers can upload their pictures to a website to review different sunglass styles, or virtually try on clothes.
Equally important, flexible manufacturing technologies exist to support such product customization at a mass scale. For example, 3D printing and various other automation technologies make one-of-a-kind, serial production possible. Alptekinoglu said he expects that the economics of such technologies, which are constantly improving, will naturally point the fashion industry toward mass customization.
Studies
To test the business model, the researchers conducted a pre-test, followed by two studies to investigate consumers' reactions to varying degrees of the mass customization of T-shirts.
In the first study, 237 undergraduate students were randomly assigned to participate in person, where the team examined the effects of four customers' involvement points—design, fabrication and use—on their willingness to pay for and hold onto the T-shirts. The customers could opt for ready-made T-shirts produced by the firm, or what the researchers termed "use."
Alternatively, they could personalize their T-shirt by selecting from a range of existing colors and images provided by the firm, or "assembly." For more extensive customization, customers could create their own custom color and select from the firm's library of pre-existing images, or "fabrication." For the ultimate level of personalization, called "design," customers had the freedom to design a completely unique T-shirt by crafting their own custom color and image.
In the second study, the focus shifted to exploring different approaches to a single point of customer involvement in mass customization. The team recruited 501 U.S. participants, randomly assigning them to five different groups representing distinct customization conditions. The researchers specifically investigated the influence of providing sample images in the design condition on how much the participants would pay for and how long they would keep the customized products.
By randomly assigning participants to one of these conditions, the researchers were able to test how different aspects of customer involvement affect the overall mass customization experience and its consequences.
Future work
According to the researchers, there is still more work to be done.
"While the basic idea is applicable to many other industries with significant interest in mass customization, like auto and furniture, the current supply chain structures and consumer behavioral dynamics in those industries can be vastly different," Alptekinoglu said. "So, expanding to other product categories while respecting those differences might be very useful."
One of the limitations of the study is that the researchers recruited mostly students from western cultures, so a next research step would be to investigate if there are similar customer behaviors in other countries and cultures.
Guide said another action step would be more outreach to move this research from the laboratory and into real life.
"I'm used to taking what I'm doing and bringing it to a company to get them to tell me what they think about the concept," Guide said. "I'd like to see us make an effort to get this information out to these managers."
Guide said that the research team's unique interdisciplinary approach—in this case, joining supply chain with marketing scientists together—will be helpful in investigating solutions to fast fashion's environmental impact.
"We have a team who are used to working with each other," Guide said. "And each member knows an area—such as behavioral marketing and analytical modeling—and that interdisciplinary approach helps us look at the question of sustainability that is solution-based, that businesses will be willing to adopt."
More information: Aydin Alptekinoglu et al, Can mass customization slow fast fashion down? The impact on time‐to‐disposal and willingness‐to‐pay, Journal of Operations Management (2023). DOI: 10.1002/joom.1255
Charged ions interacting with the Earth’s magnetic field often create auroras near the planet’s poles. The aurora australis or the “southern lights,” are captured here by a NASA satellite. Credit: NASA Earth Observatory.
The iron atoms that make up the Earth's solid inner core are tightly jammed together by astronomically high pressures—the highest on the planet.
But even here, there's space for wiggle room, researchers have found.
A study led by The University of Texas at Austin and collaborators in China found that certain groupings of iron atoms in the Earth's inner core are able to move about rapidly, changing their places in a split second while maintaining the underlying metallic structure of the iron—a type of movement known as "collective motion" that's akin to dinner guests changing seats at a table.
The results, which were informed by laboratory experiments and theoretical models, indicate that atoms in the inner core move around much more than previously thought.
The results could help explain numerous intriguing properties of the inner core that have long vexed scientists, as well as help shed light on the role the inner core plays in powering Earth's geodynamo—the elusive process that generates the planet's magnetic field.
"Now, we know about the fundamental mechanism that will help us with understanding the dynamic processes and evolution of the Earth's inner core," said Jung-Fu Lin, a professor at the UT Jackson School of Geosciences and one of the study's lead authors.
It's impossible for scientists to directly sample the Earth's inner core because of its extremely high temperatures and pressures. So, Lin and collaborators re-created it in miniature in the lab by taking a small iron plate and shooting it with a fast-moving projectile. The temperature, pressure and velocity data collected during the experiment was then put into a machine-learning computer model of atoms in the inner core.
Scientists think that iron atoms in the inner core are arranged in a repeating hexagonal configuration. According to Lin, most computer models portraying the lattice dynamics of iron in the inner core show only a small number of atoms—usually fewer than a hundred. But using an AI algorithm, the researchers were able to significantly beef up the atomic environment, creating a "supercell" of about 30,000 atoms to more reliably predict iron's properties.
At this supercell scale, the scientists observed groups of atoms moving about, changing places while still maintaining the overall hexagonal structure.
The researchers said that the atomic movement could explain why seismic measurements of the inner core show an environment that's much softer and malleable than would be expected at such pressures, said co-lead author Youjun Zhang, a professor at Sichuan University.
A model of iron atoms on the move in Earth's inner core. Credit: Youjun Zhang et al.
"Seismologists have found that the center of the Earth, called the inner core, is surprisingly soft, kind of like how butter is soft in your kitchen," he said. "The big discovery that we've found is that solid iron becomes surprisingly soft deep inside the Earth because its atoms can move much more than we ever imagined. This increased movement makes the inner core less rigid, weaker against shear forces."
The researchers said that searching for an answer to explain the "surprisingly soft" physical properties reflected in the seismic data is what motivated their research.
About half of the geodynamo energy that generates the Earth's magnetic field can be attributed to the inner core, according to the researchers, with the outer core making up the rest. The new insight on inner core activity at the atomic scale can help inform future research on how energy and heat are generated in the inner core, how it relates to the dynamics of the outer core, and how they work together to generate the planet's magnetic field that is a key ingredient for a habitable planet.
More information: Youjun Zhang et al, Collective motion in hcp-Fe at Earth's inner core conditions, Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2309952120
The CAS-ESM team discussed the simulation results of fully coupled atmospheric CO2seasonal variations while examining visualizations on the suspended dome screen at the Earth System Numerical Simulation Facility (EarthLab). Credit: Guoqiang Li
The Chinese Academy of Sciences Earth System Model (CAS-ESM2.0), a sophisticated Earth modeling tool, has achieved a major breakthrough in fully coupled atmospheric CO2 simulation, as revealed in Advances in Atmospheric Sciences.
The study was conducted by researchers from the Institute of Atmospheric Physics of the Chinese Academy of Sciences, Beijing Normal University and Stony Brook University.
Their findings highlight CAS-ESM2.0's exceptional capability in two-way coupling of terrestrial and marine carbon cycles, along with atmospheric CO2, enabling accurate spatiotemporal assessments of atmospheric CO2 changes.
Atmospheric CO2, a pivotal greenhouse gas, has surged since the Industrial Revolution, significantly affecting both the global climate, leading to warming through the greenhouse effect, and ecosystems by enhancing plant photosynthesis. It remains central to worldwide climate and environmental research.
Earth system models play a vital role in studying atmospheric CO2 concentration changes and their complex interactions with climate across different spatiotemporal scales. Achieving full coupling of atmospheric CO2 in these models has long been a challenge, particularly in emissions-driven simulations, where CO2 interacts with land and ocean carbon cycles. This complexity presents numerous challenges and uncertainties.
CAS-ESM2 is capable of reasonably simulating the increasing trend of atmospheric CO2 from 1850 to 2014, as well as the response of land and ocean net carbon fluxes. Credit: Jiawen Zhu and GPVis Visualization Team
Over several decades, CAS-ESM has undergone continuous development, culminating in the release of CAS-ESM2.0. This latest version has completed the sixth phase of the Coupled Model Intercomparison Project (CMIP6) Diagnosis, Evaluation, and Characterization of Klima (DECK) simulations (concentration-driven runs) and submitted the results to CMIP6.
The team's subsequent efforts focused on enhancing CAS-ESM2.0 to achieve two-way coupling among atmospheric CO2, the physical climate system, and the carbon cycle in land and ocean. This breakthrough empowers CAS-ESM2.0 to simulate CO2-carbon-climate interactions and autonomously calculate atmospheric CO2 concentrations.
Leveraging CAS-ESM2.0's capabilities, the researchers conducted a coupled carbon-climate simulation in alignment with CMIP6's historical emissions-driven experiment proposal. The results are remarkable, with CAS-ESM2.0 demonstrating excellent agreement with observations, accurately reproducing the rising trend of annual CO2 levels from 1850 to 2014 and capturing the seasonal CO2 cycle.
CAS-ESM's potential applications, given its ability to simulate CO2-carbon-climate interactions, are manifold. It offers a valuable tool for investigating scientific issues related to carbon-climate interactions, enabling quantification of model biases associated with specific processes, such as fire and vegetation dynamics, and revealing the underlying mechanisms.
Furthermore, CAS-ESM holds promise in supporting China's goal of carbon neutrality. By employing CAS-ESM to assess net carbon fluxes at each stage of the carbon-neutrality journey, policymakers can receive invaluable insights to refine strategies on carbon neutrality.
More information: Jiawen Zhu et al, CAS-ESM2.0 Successfully Reproduces Historical Atmospheric CO2 in a Coupled Carbon-Climate Simulation, Advances in Atmospheric Sciences (2023). DOI: 10.1007/s00376-023-3172-9
With the help of advanced sonar, the researchers can observe the water column and, in this case, the gas bubbles rising from the ocean floor to the surface. The sonar also penetrates the bottom sediments, which provides important information about the properties of the seabed and, for example, whether there is gas hidden in the sediments. Credit: Christian Stranne
During a research expedition led by Linnaeus University and Stockholm University to the deepest parts of the Baltic Sea in the Landsort Deep researchers recently discovered an area with extensive emissions of the powerful greenhouse gas methane from the bottom sediments.
The area where the methane leak was discovered is located in the Landsort Deep (Landsortsdjupet), about 30 kilometers southeast of the coastal town Nynäshamn. Christian Stranne, associate professor of marine geophysics at Stockholm University, is surprised by the discovery.
"We know that methane gas can bubble out from shallow coastal seabeds in the Baltic Sea, but I have never seen such an intense bubble release before and definitely not from such a deep area," says Christian Stranne.
A poorly understood phenomenon
The research project aims to expand knowledge about methane and its sources and sinks in the oxygen-free environments in the deeper parts of the Baltic Sea. The project is led by Marcelo Ketzer, professor of environmental science at Linnaeus University.
"Knowledge about the factors that control how much methane is produced in these deeper areas and where the methane goes is limited. How does the system react to, for example, eutrophication or a warmer climate? I knew from one of my previous projects that the methane levels in the sediments in this area are higher than elsewhere in the Baltic Sea, but I never expected methane to bubble out into the sea in this way," says Marcelo Ketzer.
The researchers determined the area's extent to be about 20 square kilometers (equivalent to almost 4,000 football pitches) and it lies at a depth of around 400 meters. During the expedition, a large number of sediment cores and water samples were collected, and now the researchers hope that further analyses will be able to provide answers to why so much methane gas is released from this specific area.
"We already have a pretty good idea of why it looks the way it does. The size of the sediment grains in the area and the form of the seafloorgive us an indication. It seems like deep ocean currents are causing sediments to accumulate in this particular area, but we need to do more detailed analyses before we can say anything definitive," says Marcelo Ketzer.
The bubbles rise to the surface of the sea
Another interesting discovery made during the expedition concerns how high up through the water column the methane bubbles rise.
"At the depths we are working with here, you can expect the methane bubbles to reach at most perhaps 150–200 meters from the seabed. The methane in the bubbles dissolves in the ocean and therefore they usually gradually decrease in size as they rise towards the sea surface," says Christian Stranne.
"It is actually quite a complicated balance between pressure effects and diffusion of gases that together determine how size and gas composition develop in a bubble, but the net effect for smaller bubbles is that they lose both size and rise velocity with increased distance from the bottom."
To the researchers' great surprise, they could see some bubbles rising to 370 meters from the ocean floor.
"Bubbles from deep-sea sediments (around a thousand meters and deeper) can rise significantly higher due to a coating of 'frozen methane' that forms around the bubble," says Stranne.
"This summer I participated in a French expedition to the Amazon outlet where we observed bubbles rising up to 700 meters above the seabed. But I don't know of any study where such persistent bubbles have been observed at these depths—it could be a new world record, and it could force us to re-evaluate the role of deep basins in the Baltic Sea, in terms of contribution to the surface water methane content."
Oxygen-free bottoms mighty be the explanation
The researchers have so far not been able to find out exactly how high the bubbles reach. From the sonar, they can see bubbles to at least 40 meters from the sea surface, but it may well be that some bubbles reach significantly higher than that. One of the explanations may be that the bubbles are unusually large, but the researchers have an alternative explanation that they consider more likely.
"Rather, we believe that it is linked to the oxygen-free conditions in the deep water of the Baltic Sea. If there is no oxygen, the levels of dissolved methane in the ocean can be relatively high, which in turn leads to the bubbles not losing methane as quickly. The bubbles are thus kept more intact in this environment, which means that methane transport towards the sea surface becomes more efficient," says Stranne.
"It is a hypothesis that we are currently investigating and if it proves to be correct, it could have consequences—if the oxygen conditions in the Baltic Sea deteriorate further, it would probably lead to a greater transport of methane from the deeper parts of the Baltic Sea, but it remains to be investigated how much may leak into the atmosphere."
Marcelo Ketzer and Christian Stranne believe that methane gas emissions similar to those discovered in the Landsort Deep may also occur in other places in the Baltic Sea.
"Now we know what to look for and we look forward to testing this model in other areas of the Baltic Sea with similar geological conditions. There are potentially another half dozen places to explore," Marcelo Ketzer adds.
