Born to modulate: Researchers reveal origins of climate-controlling particles
Ephemeral and mysterious, aerosol particles burden climate projections with uncertainty. New particle formation pathways developed by PNNL scientists lift the veil.
DOE/Pacific Northwest National Laboratory
Aerosol particles are tiny. Swirling suspended in the air around us, most are smaller than the smallest bug, thinner than the thinnest hair on your head, gossamer specks practically invisible to the naked eye. Newly formed ones are nano-sized. Yet their influence is gargantuan.
They determine the color of sunsets. They inflict over three million premature deaths each year. And the power they hold over our climate is massive.
Despite their outsized effect, aerosols are shrouded in mystery. How do new aerosol particles come to be? Where are they born, and under what conditions? Such questions have troubled climate scientists for decades and imbued climate models with lingering uncertainty.
In new work, a team led by scientists at the Department of Energy’s Pacific Northwest National Laboratory have finally answered some of the most fundamental questions about how new aerosol particles come to exist. By accounting for molecular-level interactions between substances that make up these tiny particles in an Earth system model, the team, whose work is carried out under the project named EAGLES (Enabling Aerosol-cloud interactions at GLobal convection-permitting scalES), achieved three major milestones.
They integrated 11 new pathways by which new aerosol particles form into a global climate model, identified where in the world those pathways are unfolding, and assessed their potential impacts on Earth’s climate.
“Properly representing new particle formation has been a thorn in our sides for quite some time,” said Earth scientist and the principal investigator of EAGLES, Po-Lun Ma. “Now that we’ve identified these new mechanisms, our results stand to do two important things: substantially dial down what has been the largest source of uncertainty in aerosol-climate science to date and improve our ability to predict how the Earth system could change.”
Their results were recently published in Nature. The work represents a collaborative effort across many institutions.
Ephemeral and mysterious, aerosol particles burden climate projections with uncertainty. New particle formation pathways developed by PNNL scientists lift the veil.
DOE/Pacific Northwest National Laboratory
Aerosol particles are tiny. Swirling suspended in the air around us, most are smaller than the smallest bug, thinner than the thinnest hair on your head, gossamer specks practically invisible to the naked eye. Newly formed ones are nano-sized. Yet their influence is gargantuan.
They determine the color of sunsets. They inflict over three million premature deaths each year. And the power they hold over our climate is massive.
Despite their outsized effect, aerosols are shrouded in mystery. How do new aerosol particles come to be? Where are they born, and under what conditions? Such questions have troubled climate scientists for decades and imbued climate models with lingering uncertainty.
In new work, a team led by scientists at the Department of Energy’s Pacific Northwest National Laboratory have finally answered some of the most fundamental questions about how new aerosol particles come to exist. By accounting for molecular-level interactions between substances that make up these tiny particles in an Earth system model, the team, whose work is carried out under the project named EAGLES (Enabling Aerosol-cloud interactions at GLobal convection-permitting scalES), achieved three major milestones.
They integrated 11 new pathways by which new aerosol particles form into a global climate model, identified where in the world those pathways are unfolding, and assessed their potential impacts on Earth’s climate.
“Properly representing new particle formation has been a thorn in our sides for quite some time,” said Earth scientist and the principal investigator of EAGLES, Po-Lun Ma. “Now that we’ve identified these new mechanisms, our results stand to do two important things: substantially dial down what has been the largest source of uncertainty in aerosol-climate science to date and improve our ability to predict how the Earth system could change.”
Their results were recently published in Nature. The work represents a collaborative effort across many institutions.
Particle hotspots
Aerosol particles come about in different ways. Some, known as primary aerosols, are ejected straight into the atmosphere, like dust from a desert or ash from a volcano. Others are born in the sky, products of gases that intermingle in the atmospheric milieu—these are the particles that claim the EAGLES team’s attention.
New particles aren’t born just anywhere; there are hotspots. Much of the action happens above forests, like the rainforests of the Central Amazon and Southeast Asia.
There, “clean” air free of primary aerosols allows for the right kind of chemical intermingling that gives way to new particles. Scientists have detected huge concentrations of new particles above these forests.
But climate models today are partly blind to these big particle peaks. When pressed to estimate how many particles are present or where in the atmosphere they show up, even the best models greatly underestimate their abundance or misidentify at which altitudes they appear.
Thanks to the new pathways put together by the EAGLES team, however, this blind spot is now being made clear. When the team plugged the pathways into DOE’s Earth system model, E3SM, the particle peaks matched what they had seen in real-world observations.
Not only did the revised model correctly simulate the quantity of these particles, it also matched where researchers had found them during field campaigns, correctly identifying that many of the new particles show up in the upper troposphere. The team found similar success in matching model predictions to real-world measurements in other hotspots, like above oceans and cities.
When they took a worldwide view, the team found the average global concentration of these particles was nearly triple the amount estimated using traditional methods.
Aerosol particles come about in different ways. Some, known as primary aerosols, are ejected straight into the atmosphere, like dust from a desert or ash from a volcano. Others are born in the sky, products of gases that intermingle in the atmospheric milieu—these are the particles that claim the EAGLES team’s attention.
New particles aren’t born just anywhere; there are hotspots. Much of the action happens above forests, like the rainforests of the Central Amazon and Southeast Asia.
There, “clean” air free of primary aerosols allows for the right kind of chemical intermingling that gives way to new particles. Scientists have detected huge concentrations of new particles above these forests.
But climate models today are partly blind to these big particle peaks. When pressed to estimate how many particles are present or where in the atmosphere they show up, even the best models greatly underestimate their abundance or misidentify at which altitudes they appear.
Thanks to the new pathways put together by the EAGLES team, however, this blind spot is now being made clear. When the team plugged the pathways into DOE’s Earth system model, E3SM, the particle peaks matched what they had seen in real-world observations.
Not only did the revised model correctly simulate the quantity of these particles, it also matched where researchers had found them during field campaigns, correctly identifying that many of the new particles show up in the upper troposphere. The team found similar success in matching model predictions to real-world measurements in other hotspots, like above oceans and cities.
When they took a worldwide view, the team found the average global concentration of these particles was nearly triple the amount estimated using traditional methods.
Climate-controlling clouds
Aerosols and clouds have a close-knit relationship. Aerosol particles are the seeds of clouds. Atmospheric moisture condenses on aerosol particle surfaces, one water molecule clotting after another like strands of cotton candy layering atop a cone.
A particle’s properties—its chemical composition, its size and structure—shape the traits of the resulting cloud that forms around it. One particle type might make its corresponding cloud more or less likely to rain. Another might determine whether a cloud reflects more or less sunlight, in turn determining whether the Earth’s atmosphere warms more or less.
In this way, clouds and aerosol particles control much of our weather and climate. They can warm, cool or even alter the structure and flow of the Earth’s atmosphere.
Many scientists believe that new particles—the kind the EAGLES team is trying to understand—make up roughly half the world’s seeds that later become clouds. In the new work, however, the team shows that these particles could, in some regions, be responsible for even more.
Over the tropical and mid-latitude oceans, locally generated new particles could account for up to 80 percent of the material upon which clouds condense. Over Europe and the Eastern United States, they could account for 65 percent of the seed material for clouds.
Aerosols and clouds have a close-knit relationship. Aerosol particles are the seeds of clouds. Atmospheric moisture condenses on aerosol particle surfaces, one water molecule clotting after another like strands of cotton candy layering atop a cone.
A particle’s properties—its chemical composition, its size and structure—shape the traits of the resulting cloud that forms around it. One particle type might make its corresponding cloud more or less likely to rain. Another might determine whether a cloud reflects more or less sunlight, in turn determining whether the Earth’s atmosphere warms more or less.
In this way, clouds and aerosol particles control much of our weather and climate. They can warm, cool or even alter the structure and flow of the Earth’s atmosphere.
Many scientists believe that new particles—the kind the EAGLES team is trying to understand—make up roughly half the world’s seeds that later become clouds. In the new work, however, the team shows that these particles could, in some regions, be responsible for even more.
Over the tropical and mid-latitude oceans, locally generated new particles could account for up to 80 percent of the material upon which clouds condense. Over Europe and the Eastern United States, they could account for 65 percent of the seed material for clouds.
The role particles play in the climate response
Understanding how aerosols influence Earth’s climate is a key part of forecasting how our world will change. As nations seek to curb global warming by reducing emissions, the climate will respond in turn. And improving climate models to closely mirror the complexity of the Earth system, said Ma, is imperative in predicting the climate response.
“Our overarching goal is to create increasingly realistic representations of the climate system,” said Ma. “And aerosols have been a major hurdle in our path toward that goal. We rely so much on Earth system models—to test emissions scenarios and predict climate responses. The more closely they mirror reality, the more confident we can be in our predictions.”
Although much mystery remains around aerosol particles, said Earth scientist Hailong Wang, a coauthor of the new work, researchers are continually chipping away at that uncertainty.
“We can’t confidently say what the full impact of their presence or absence will be until we have a solid, mechanistic understanding of aerosol particles,” said Wang. “And this research marks a significant step toward that understanding.”
This work, “Global variability in atmospheric new particle formation mechanisms,” was supported by DOE’s Biological and Environmental Research program within the Office of Science. Resources for modeling were obtained from the National Energy Research Scientific Computing Center, which is supported by DOE’s Advanced Scientific Computing program.
In addition to Ma and Wang, PNNL coauthors include Kai Zhang, Manish Shrivastava, Shuaiqi Tang, Jerome Fast, and Balwinder Singh. The findings represent a collaborative effort across multiple institutions, including Tsinghua University, the National Center for Atmospheric Research, Carnegie Mellon University, the California Institute of Technology, the Ocean University of China, Nanjing University, Xiamen University, and Fudan University.
Understanding how aerosols influence Earth’s climate is a key part of forecasting how our world will change. As nations seek to curb global warming by reducing emissions, the climate will respond in turn. And improving climate models to closely mirror the complexity of the Earth system, said Ma, is imperative in predicting the climate response.
“Our overarching goal is to create increasingly realistic representations of the climate system,” said Ma. “And aerosols have been a major hurdle in our path toward that goal. We rely so much on Earth system models—to test emissions scenarios and predict climate responses. The more closely they mirror reality, the more confident we can be in our predictions.”
Although much mystery remains around aerosol particles, said Earth scientist Hailong Wang, a coauthor of the new work, researchers are continually chipping away at that uncertainty.
“We can’t confidently say what the full impact of their presence or absence will be until we have a solid, mechanistic understanding of aerosol particles,” said Wang. “And this research marks a significant step toward that understanding.”
This work, “Global variability in atmospheric new particle formation mechanisms,” was supported by DOE’s Biological and Environmental Research program within the Office of Science. Resources for modeling were obtained from the National Energy Research Scientific Computing Center, which is supported by DOE’s Advanced Scientific Computing program.
In addition to Ma and Wang, PNNL coauthors include Kai Zhang, Manish Shrivastava, Shuaiqi Tang, Jerome Fast, and Balwinder Singh. The findings represent a collaborative effort across multiple institutions, including Tsinghua University, the National Center for Atmospheric Research, Carnegie Mellon University, the California Institute of Technology, the Ocean University of China, Nanjing University, Xiamen University, and Fudan University.
Journal
Nature
Nature
DOI
Article Title
Global variability in atmospheric new particle formation mechanisms
Global variability in atmospheric new particle formation mechanisms
Not the day after tomorrow: Why we can't predict the timing of climate tipping points
A new study published in Science Advances reveals that uncertainties are currently too large to accurately predict exact tipping times for critical Earth system components like the Atlantic Meridional Overturning Circulation (AMOC), polar ice sheets, or tropical rainforests. These tipping events, which might unfold in response to human-caused global warming, are characterized by rapid, irreversible climate changes with potentially catastrophic consequences. However, as the new study shows, predicting when these events will occur is more difficult than previously thought.
Climate scientists from the Technical University of Munich (TUM) and the Potsdam Institute for Climate Impact Research (PIK) have identified three primary sources of uncertainty. First, predictions rely on assumptions regarding the underlying physical mechanisms, as well as regarding future human actions to extrapolate past data into the future. These assumptions can be overly simplistic and lead to significant errors. Second, long-term, direct observations of the climate system are rare and the Earth system components in question may not be suitably represented by the data. Third, historical climate data is incomplete. Huge data gaps, especially for the longer past, and the methods used to fill these gaps can introduce errors in the statistics used to predict possible tipping times.
To illustrate their findings, the authors examined the AMOC, a crucial ocean current system. Previous predictions from historical data suggested a collapse could occur between 2025 and 2095. However, the new study revealed that the uncertainties are so large that these predictions are not reliable. Using different fingerprints and data sets, predicted tipping times for the AMOC ranged from 2050 to 8065 even if the underlying mechanistic assumptions were true. Knowing that the AMOC might tip somewhere within a 6000-year window isn't practically useful, and this large range highlights the complexity and uncertainty involved in such predictions.
The researchers conclude that while the idea of predicting climate tipping points is appealing, the reality is fraught with uncertainties. The current methods and data are not up to the task. “Our research is both a wake-up call and a cautionary tale,” says lead author Maya Ben-Yami. “There are things we still can’t predict, and we need to invest in better data and a more in-depth understanding of the systems in question. The stakes are too high to rely on shaky predictions.”
While the study by Ben-Yami and colleagues shows that we cannot reliably predict tipping events, the possibility of such events cannot be ruled out either. The authors also stress that statistical methods are still very good at telling us which parts of the climate have become more unstable. This includes not only the AMOC, but also the Amazon rainforest and ice sheets. “The large uncertainties imply that we need to be even more cautious than if we were able to precisely estimate a tipping time. We still need to do everything we can to reduce our impact on the climate, first and foremost by cutting greenhouse gas emissions. Even if we can’t predict tipping times, the probability for key Earth system components to tip still increases with every tenth of a degree of warming,” concludes co-author Niklas Boers.
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This research is part of the ClimTip project, which aims to enhance our understanding of climate tipping points.
For additional information or to schedule an interview with the researchers, please contact Niklas Boers at boers@pik-potsdam.de.
More details, including a copy of the paper, can be found online at the Science Advances press package at https://www.eurekalert.org/press/vancepak/. You will need your user ID and password to access this information.
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Reference:
M. Ben-Yami, A. Morr, S. Bathiany, N. Boers: Uncertainties too large to predict tipping times of major Earth system components from historical data, Science Advances (2024).
The article will be made available at https://www.science.org/doi/10.1126/sciadv.adl4841 once it is published.
Journal
Science Advances
Method of Research
Data/statistical analysis
Article Title
Uncertainties too large to predict tipping times of major Earth system components from historical data
Article Publication Date
2-Aug-2024
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