“Up till now, the magnitude of past fire activity, and thus the amount of smoke in the preindustrial atmosphere, has not been well characterized,” said Pengfei Liu, a former graduate student and postdoctoral fellow at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and first author of the paper. “These results have importance for understanding the evolution of climate change from the 1750s until today, and for predicting future climate.”

One of the biggest uncertainties when it comes to predicting the future impacts of climate change is how fast surface temperatures will rise in response to increases in greenhouse gases. Predicting these temperatures is complicated since it involves the calculation of competing warming and cooling effects in the atmosphere. Greenhouse gases trap heat and warm the planet’s surface while aerosol particles in the atmosphere from volcanoes, fires and other combustion cool the planet by blocking sunlight or seeding cloud cover. Understanding how sensitive surface temperature is to each of these effects and how they interact is critical to predicting the future impact of climate change.

Many of today’s climate models rely on past levels of greenhouse gasses and aerosols to validate their predictions for the future. But there’s a problem: While pre-industrial levels of greenhouse gasses are well documented, the amount of smoke aerosols in the preindustrial atmosphere is not.

To model smoke in the pre-industrial Southern Hemisphere, the research team looked to Antarctica, where the ice trapped smoke particles emitted from fires in Australia, Africa and South America. Ice core scientists and co-authors of the study, Joseph McConnell and Nathan Chellman from the Desert Research Institute in Nevada, measured soot, a key component of smoke, deposited in an array of 14 ice cores from across the continent, many provided by international collaborators.

“Soot deposited in glacier ice directly reflects past atmospheric concentrations so well-dated ice cores provide the most reliable long-term records,” said McConnell.

What they found was unexpected.

“While most studies have assumed less fire took place in the preindustrial era, the ice cores suggested a much fierier past, at least in the Southern Hemisphere,” said Loretta Mickley, Senior Research Fellow in Chemistry-Climate Interactions at SEAS and senior author of the paper.

To account for these levels of smoke, the researchers ran computer simulations that account for both wildfires and the burning practices of indigenous people.

“The computer simulations of fire show that the atmosphere of the Southern Hemisphere could have been very smoky in the century before the Industrial Revolution. Soot concentrations in the atmosphere were up to four times greater than previous studies suggested. Most of this was caused by widespread and regular burning practiced by indigenous peoples in the pre-colonial period,” said Jed Kaplan, Associate Professor at the University of Hong Kong and co-author of the study.

This result agrees with the ice core records that also show that soot was abundant before the start of the industrial era and has remained relatively constant through the 20th century. The modelling suggests that as land use changes decreased fire activity, emissions from industry increased.

What does this finding mean for future surface temperatures?

By underestimating the cooling effect of smoke particles in the pre-industrial world, climate models might have over-estimated the warming effect of carbon dioxide and other greenhouse gasses in order to account for the observed increases in surface temperatures.

“Climate scientists have known that the most recent generation of climate models have been over-estimating surface temperature sensitivity to greenhouse gasses, but we haven’t known why or by how much,” said Liu. “This research offers a possible explanation.”

“Clearly the world is warming but the key question is how fast will it warm as greenhouse gas emissions continue to rise. This research allows us to refine our predictions moving forward,” said Mickley.

The research was co-authored by Yang Li, Monica Arienzo, John Kodros, Jeffrey Pierce, Michael Sigl, Johannes Freitag, Robert Mulvaney and Mark Curran.

It was funded by the National Science Foundation’s Geosciences Directorate under grants AGS-1702814 and 1702830, with additional support from 0538416, 0538427, and 0839093.

The authors studied the vast, rural Loreto department of the Peruvian Amazon, where most of the 800,000 inhabitants eat fish at least once a day, or an average of about 52 kilograms (115 pounds) per year. This is their primary source not only of protein, but fatty acids and essential trace minerals including iron, zinc and calcium. Unfortunately, it is not enough; a quarter of all children are malnourished or stunted, and more than a fifth of women of child-bearing age are iron deficient.

Threats to Amazon fisheries, long a mainstay for both indigenous people and modern development, are legion: new hydropower dams that pen in big migratory fish (some travel thousands of miles from Andes headwaters to the Atlantic estuary and back); soil erosion into rivers from deforestation; toxic runoff from gold mines; and over-exploitation by fishermen themselves, who are struggling to feed fast-growing populations. In Loreto, catch tonnages are stagnating; some large migratory species are already on the decline, and others may be on the way. It is the same elsewhere; globally, a third of freshwater fish species are threatened with extinction, and 80 are already known to be extinct, according to the World Wildlife Fund.

Different species of animals and plants contain different ratios of nutrients, so biodiversity is key to adequate human nutrition, say the researchers. “If fish decline, the quality of the diet will decline,” said the study’s senior coauthor, Shahid Naeem, director of Columbia University’s Earth Institute Center for Environmental Sustainability. “Things are definitely declining now, and they could be on the path to crashing eventually.”

To study the region’s fish, the study’s lead author, then-Columbia PhD. student Sebastian Heilpern, made numerous shopping trips to the bustling Belén retail market in the provincial capital of Iquitos. He also visited the city’s Amazon River docks, where wholesale commerce begins at 3:30 in the morning. He and another student bought multiple specimens of as many different species as they could find, and ended up with 56 of the region’s 60-some main food species. These included modest-size scale fish known locally as ractacara and yulilla; saucer-shaped palometa (related to piranha); and giant catfish extending six feet or more. (The researchers settled for chunks of the biggest ones.)

The fish were flown on ice to a government lab in Lima, where each species was analyzed for protein, fatty acids and trace minerals. The researchers then plotted the nutritional value of each species against its probability of surviving various kinds of ongoing environmental degradation. From this, they drew up multiple scenarios of how people’s future diet would be affected as various species dropped out of the mix.

Overall, the biomass of fish caught has remained stable in recent years. However, large migratory species, the most vulnerable to human activities, comprise a shrinking portion, and as they disappear, they are being replaced by smaller local species. Most fish contain about the same amount of protein, so this has not affected the protein supply. And, the researchers found, many smaller fish in fact contain higher levels of omega-3 fatty acids, so their takeover may actually increase those supplies. On the other hand, as species compositions lean more to smaller fish, supplies of iron, zinc are already going down, and will continue to decline, they say.

“Like any other complex system, you see a tradeoff,” said Heilpern. “Some things are going up while other things are going down. But that only lasts up to a point.” Exactly which species will fill the gaps left when others decline is difficult to predict — but the researchers project that the overall nutritional value of the catch will nosedive around the point where 40 of the 60 food species become scarce or extinct. “You have a tipping point, where the species that remain can be really lousy,” said Heilpern.

One potential solution: in many places around the world where wild foods including fish and bush meat (such as monkeys and lizards) are declining, people are turning increasingly to farm-raised chicken and aquaculture — a trend encouraged by the World Bank and other powerful organizations. This is increasingly the case in Loreto. But in a separate study published in March, Heilpern, Naeem and their colleagues show that this, too, is undermining human nutrition.

The researchers observed that chicken production in the region grew by about three quarters from 2010 to 2016, and aquaculture nearly doubled. But in analyzing the farmed animals’ nutritional values, they found that they typically offer poorer nutrition than a diverse mix of wild fish. In particular, the move to chicken and aquaculture will probably exacerbate the region’s already serious iron deficiencies, and limit supplies of essential fatty acids, they say. “Because no single species can offer all key nutrients, a diversity of species is needed to sustain nutritionally adequate diets,” they write.

Besides this, chicken farming and aquaculture exert far more pressure on the environment than fishing. In addition to encouraging clearing of forests to produce feed for the animals, animal farming produces more more greenhouse gases, and introduces fertilizers and other pollutants into nearby waters, says Heilpern.

“Inland fish are fundamental for nutrition in many low-income and food-deficit countries, and of course landlocked countries,” said John Valbo Jørgensen, a Rome-based expert on inland fisheries with the UN Food and Agriculture Organization. “Many significant inland fisheries, including those of Peru, take place in remote areas with poor infrastructure and limited inputs. It will not be feasible to replace those fisheries with farmed animals including fish.”

Heilpern is now working with the Wildlife Conservation Society to produce an illustrated guide to the region’s fish, including their nutritional values, in hopes of promoting a better understanding of their value among both fishermen and consumers.

The other authors of the new study are Ruth deFries and Maria Uriarte of the Earth Institute; and Kathryn Fiorella, Alexander Flecker and Suresh Sethi of Cornell University.

The team, led by Hong Chen, assistant professor of biomedical engineering in the McKelvey School of Engineering and of radiation oncology at the School of Medicine, is the first to provide direct evidence showing noninvasive, cell-type-specific activation of neurons in the brain of mammal by combining ultrasound-induced heating effect and genetics, which they have named sonothermogenetics. It is also the first work to show that the ultrasound- genetics combination can robustly control behavior by stimulating a specific target deep in the brain.

Results of the three years of research, which was funded in part by the National Institutes of Health’s BRAIN Initiative, were published online in Brain Stimulation May 11, 2021.

The senior research team included experts from both the McKelvey School of Engineering and the School of Medicine, including Jianmin Cui, professor of biomedical engineering; Joseph P. Culver, professor of radiology, of physics and of biomedical engineering; Mark J. Miller, associate professor of medicine in the Division of Infectious Diseases in the Department of Medicine; and Michael Bruchas, formerly of Washington University, now professor of anesthesiology and pharmacology at the University of Washington.

“Our work provided evidence that sonothermogenetics evokes behavioral responses in freely moving mice while targeting a deep brain site,” Chen said. “Sonothermogenetics has the potential to transform our approaches for neuroscience research and uncover new methods to understand and treat human brain disorders.”

Using a mouse model, Chen and the team delivered a viral construct containing TRPV1 ion channels to genetically-selected neurons. Then, they delivered small burst of heat via low-intensity focused ultrasound to the select neurons in the brain via a wearable device. The heat, only a few degrees warmer than body temperature, activated the TRPV1 ion channel, which acted as a switch to turn the neurons on or off.

“We can move the ultrasound device worn on the head of free-moving mice around to target different locations in the whole brain,” said Yaoheng Yang, first author of the paper and a graduate student in biomedical engineering. “Because it is noninvasive, this technique has the potential to be scaled up to large animals and potentially humans in the future.”

The work builds on research conducted in Cui’s lab that was published in Scientific Reports in 2016. Cui and his team found for the first time that ultrasound alone can influence ion channel activity and could lead to new and noninvasive ways to control the activity of specific cells. In their work, they found that focused ultrasound modulated the currents flowing through the ion channels on average by up to 23%, depending on channel and stimulus intensity. Following this work, researchers found close to 10 ion channels with this capability, but all of them are mechanosensitive, not thermosensitive.

The work also builds on the concept of optogenetics, the combination of the targeted expression of light-sensitive ion channels and the precise delivery of light to stimulate neurons deep in the brain. While optogenetics has increased discovery of new neural circuits, it is limited in penetration depth due to light scattering and requires surgical implantation of optical fibers.

Sonothermogenetics has the promise to target any location in the mouse brain with millimeter-scale resolution without causing any damage to the brain, Chen said. She and the team continue to optimize the technique and further validate their findings.

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The research provides series of dynamic variations of conversion factors depending on possible trajectories of global warming to lessen the economic cost while maintaining some stability to anticipate the implementation of policies. They took into consideration different scenarios, one in which we reach the Paris Agreement’s objectives of stabilization at 2°C and 1.5°C and others in which we would overshoot these objectives and need to strengthen efforts later on. These overshoot scenarios are a violation of the Paris Agreement, but the authors argued that such possibilities cannot be ruled out, in view of the near-term climate policies currently. They further noted that the feasibility of these scenarios still depends on very deep mitigation needed later in this century. They applied conversion factors in the numerical model and simulated the additional mitigation costs in all these scenarios to target the most favourable values.

The choice of a common conversion factor

A conversion system into CO₂ equivalent is used to determine the participation of different GHG on a given time to prioritize actions. A well-known example is the global warming potential (GWP). To enable comparison among the parties of the Paris Agreement, the 100-year global warming potential (GWP100) was chosen as a reference. Greenhouse gases having very different lifespan and radiative impact, this conversion system is dependent on the choice of a time horizon.

“With GWP100 we look at the cumulative greenhouse effect on a 100-year period, which for methane gives a conversion factor of 28. This means 1 kilogram of methane is 28 times more potent than a kilogram of CO₂” explains Johannes Morfeldt, a collaborator of this study joined from Sweden. Yet, since methane has a shorter lifespan and a higher radiative impact than CO₂, the cumulative effect on 20 years (GWP20) is much more significant: 84 times more than 1 kilogram of CO₂.

Changing the time horizon changes the conversion factor, and therefore influences which gas gets high on the agenda. If a kilogram of methane is 84 times more important than one of CO₂, it will be more efficient to lower the global emissions by reducing methane. A debate is in motion since the nineties regarding which conversion factor should be used, and this team of researchers meant to bring additional information on their economic cost in light of possible pathways of global warming.

“We realized with our model that GWP100 is good for the coming decades, but is far from ideal in the long run” says Philippe Ciais, one of the co-authors of the study. “We don’t see much variation in an optimal scenario of stabilization at 2°C. But in the event of an overshoot scenario we observe a high discrepancy among ideal conversion factors for today and when we reach 2°C of global warming. If we do not have a dynamic approach to change these values along the way, then society will bear an additional cost to mitigate climate change” adds Olivier Boucher, another co-author.

An optimal agenda

The researchers then modelled these additional costs to estimate which conversion factor would be ideal at a given time for different temperature trajectories. They showed that setting in stone GWP100 would bring about additional mitigation costs that could be avoided by switching to a dynamic factor. In a scenario of stabilization at 2°C these additional costs round up near 2%, but in high overshoot scenarios it goes up to 5%. “This shows that the ideal factors of conversion depend on a time horizon but are also primarily determined by the pathway, and strongly influenced by a temperature overshoot” underlines Daniel Johansson, a Swedish co-author.

This study shows that adapting to possible trajectories by switching from GWP100 to shorter time-horizons in the future could spare additional mitigation costs compared to the sole use of GWP100. The researchers also understand that these values cannot continuously change to enable policies to be anticipated and implemented. Thus, they put forward series of simple combinations of cost-effective conversion factors depending on the possible pathways. The authors suggest that “the UNFCCC and Parties to the Paris Agreement consider adapting the choice of conversion factors to the future pathway as it unfolds, to implement the cheapest options to reduce greenhouse gases emissions.”

As we do not know yet the long-term pathway, the matter of the cost-effectiveness could be included in the technical assessment supporting the global stocktake within the UNFCCC. This key element of the Paris Agreement evaluates every five years the countries’ collective progress toward long-term goals and aims at increasing the level of ambition of national policies. An inclusion of cost-effectiveness of factors of conversion on this recurring stocktaking process could allow the necessary assessment in time to inform following sessions as the long-term pathway unfolds.

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“These new data reveal molecular-level differences that allow us to view the anterior and posterior hippocampus in a whole new way,” says study leader Genevieve Konopka, Ph.D., associate professor of neuroscience at UTSW.

She and study co-leader Bradley C. Lega, M.D., associate professor of neurological surgery, neurology, and psychiatry, explain that the human hippocampus is typically considered a uniform structure with key roles in memory, spatial navigation, and regulation of emotions. However, some research has suggested that the two ends of the hippocampus — the anterior, which points downward toward the face, and the posterior, which points upward toward the back of the head — take on different jobs.

Scientists have speculated that the anterior hippocampus might be more important for emotion and mood, while the posterior hippocampus might be more important for cognition. However, says Konopka, a Jon Heighten Scholar in Autism Research, researchers had yet to explore whether differences in gene activity exist between these two halves.

For the study, Konopka and Lega, both members of the Peter O’Donnell Jr. Brain Institute, and their colleagues isolated samples of both the anterior and posterior hippocampus from five patients who had the structure removed to treat epilepsy. Seizures often originate from the hippocampus, explains Lega, who performed the surgeries. Although brain abnormalities trigger these seizures, microscopic analysis suggested that the tissues used in this study were anatomically normal.

After removal, the samples underwent single nuclei RNA sequencing (snRNA-seq), which assesses gene activity in individual cells. Although snRNA-seq showed mostly the same types of neurons and support cells reside in both sections of the hippocampus, activity of specific genes in excitatory neurons — those that stimulate other neurons to fire — varied significantly between the anterior and the posterior portions of the hippocampus. When the researchers compared this set of genes to a list of genes associated with psychiatric and neurological disorders, they found significant matches. Genes associated with mood disorders, such as major depressive disorder or bipolar disorder, tended to be more active in the anterior hippocampus; conversely, genes associated with cognitive disorders, such as autism spectrum disorder, tended to be more active in the posterior hippocampus.

Lega notes that the more researchers are able to appreciate these differences, the better they’ll be able to understand disorders in which the hippocampus is involved.

“The idea that the anterior and posterior hippocampus represent two distinct functional structures is not completely new, but it’s been underappreciated in clinical medicine,” he says. “When trying to understand disease processes, we have to keep that in mind.”

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The authors of the new article in Journal of Clinical Medicine are Peter H. Gorman, MD, of the University of Maryland School of Medicine, Gail F. Forrest, PhD, of Kessler Foundation’s Tim and Caroline Reynolds Center for Spinal Stimulation, Dr. William Scott, of VA Maryland Healthcare System, Pierre K. Asselin, MS, Stephen Kornfeld, MD, Eunkyoung Hong, PhD, and Ann M. Spungen, EdD, of the James J. Peters VA Medical Center.

Bowel dysfunction, a common experience after spinal cord injury, can lead to chronic constipation and incontinence, causing discomfort and frustration. In one survey, more than a third of men with spinal cord injury reported that bowel and bladder dysfunction had the most significant effect on their lives post-injury. Unfortunately, these issues are not easily managed.

Rehabilitation professionals have traditionally managed bowel dysfunction using approaches that target the gastrointestinal system or require manual intervention, but some newer research suggests that physical activity and upright posture may enhance bowel motility. However, few studies have explored the possibility that exoskeletal-assisted walking — in which a person with spinal cord injury wears a robotic suit, enabling them to stand and walk — may be an effective addition to existing intervention plans.

In this study, the research team investigated whether exoskeletal-assisted walking improved bowel function in people with chronic spinal cord injury. They performed a three-center, randomized, controlled, crossover clinical trial in which 50 participants completed 36 sessions of exoskeletal-assisted walking. The researchers evaluated bowel function as a secondary outcome in 49 participants. Bowel function was measured via a 10-question bowel function survey, the Bristol Stool Form Scale, and the Spinal Cord Injury Quality of Life Bowel Management Difficulties instrument.

Results showed that the exoskeletal-assisted walking program provided some improvement in bowel function when compared to a control group. “We saw a notable reduction in bowel evacuation time, with 24 percent of participants reporting an improved experience,” said Dr. Forrest, co-author and associate director of the Center for Mobility and Rehabilitation Engineering Research at Kessler Foundation. “We also noted that participants’ stools trended toward better consistency, supporting our hypothesis that this intervention may improve several measures of bowel function.”

“Our results support the idea that walking, and not just standing, may have a beneficial effect on bowel function,” said Dr. Gorman, co-author and chief of the Division of Rehabilitation Medicine at the University of Maryland Rehabilitation and Orthopaedic Institute. “Our goal is to improve the quality of life of those with chronic spinal cord injury, and these encouraging results will help inform future studies on the emerging field of mobility intervention.”

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