“Liver fibrosis is the critical feature that creates chronic liver disease and liver cancer. If we can keep fibrosis in check then we can meaningfully impact liver disease,” said Tamer Sallam, MD, corresponding author of the study and vice chair and associate professor in the department of medicine at the David Geffen School of Medicine at UCLA.

“For decades we have believed that targeting inflammation is one of the most important ways to reduce MAFLD. But this new research indicates that inflammation, while still important, may not be the main driver of fibrosis.”

The study, published in the Journal of Clinical Investigation, looked specifically at a protein called lipopolysaccharide binding protein (LBP), which is involved in the body’s immune response, and how LBP functions in mice. Findings showed that mice without LBP in their liver cells had lower levels of liver inflammation and better liver function but no change in fibrosis.

In addition to mouse models, the researchers also studied genetic analyses from large human datasets and human tissue samples from MAFLD patients at different stages in the disease, to examine the consequence of loss of LBP function. The evidence combined showed that the LBP does not alter scar tissue markers.

Sallam indicated a need to further explore how LBP influences inflammation and whether other factors can offer a more potent reduction in inflammation and have an impact on reducing fibrosis.

“Reducing scar burden is one of the holy grails in the treatment of advanced liver diseases,” Sallam said. “These results suggest that certain ways of targeting inflammation may not be a viable option and that more directed therapies against other pathways could help us better target fibrosis and improve outcomes for patients.”

The remarkable two-day event, which occurred in mid-January 2022, injected vast amounts of volcanic aerosols and water vapor into the atmosphere. Historically, large volcanic eruptions like Tambora in 1815 and Mt. Pinatubo in 1991 have led to significant cooling effects on the global climate by blocking sunlight with their aerosols. However, Hunga Tonga’s eruption presented a unique scenario: As a submarine volcano, it introduced an unprecedented amount of water vapor into the stratosphere, increasing total stratospheric water content by about 10%.

Because water vapor is a powerful greenhouse gas, Dessler says there was initial speculation that it might account for the extreme global warmth in 2023 and 2024. Instead, the results of the team’s research, published Wednesday (July 24) in the Journal of Geophysical Research: Atmospheres, reveal the opposite: The eruption actually contributed to cooling the Earth, similar to other major volcanic events.

A Volcanic Eruption’s Cooling Effect

The team’s paper, titled “Evolution of the Climate Forcing During the Two Years after the Hunga Tonga-Hunga Ha’apai Eruption,” includes insight and analysis from Dessler, a professor in the Texas A&M Department of Atmospheric Sciences and the director of the Texas Center for Climate Studies; first author Dr. Mark Schoeberl, chief scientist at the Virginia-based Science and Technology Corporation in Hamburg, Virginia; and multiple scientists from the National Aeronautics and Space Administration (NASA).

Their methodology involved analyzing NASA and National Oceanic and Atmospheric Administration (NOAA) satellite data observations of aerosols and water vapor, among other variables, to estimate the energy balance of the Earth’s climate system. Their analysis revealed that the eruption resulted in more energy leaving the climate system than entering it, thereby inducing the slight cooling effect.

“Our paper pours cold water on the explanation that the eruption caused the extreme warmth of 2023 and 2024,” Dessler explained. “Instead, we need to focus primarily on greenhouse gases from human activities as the main cause of the warming, with a big assist from the ongoing El Nino.”

Implications And Future Research

According to Dessler, this research has important implications for both scientists and the general public. By dismissing the volcanic eruption as a major factor in the recent warming, the team’s study reinforces his point that human-induced greenhouse gas emissions are the primary driver of climate change. This focus is particularly relevant, given the ongoing debate and misinformation about the causes of global warming.

Moreover, Schoeberl says the study underscores the importance of continued investment in satellite-based stratospheric measurements.

“Our understanding of the Hunga Tonga eruption is largely thanks to the investment in stratospheric satellite measurements by NOAA and NASA over the past two decades,” Schoeberl added. “However, we need to be cautious about a potential ‘stratospheric data desert,’ as some of the most critical instruments are not being replaced.”

The Challenging Path Ahead

While this paper answers several important questions, Dessler acknowledges that it simultaneously introduces new ones. For instance, the researchers highlighted some unresolved issues related to the Hunga Tonga eruption, such as the unexpectedly low levels of sulfur dioxide produced by such a violent eruption and the minimal impact the eruption had on the 2023 ozone hole. The 2023 ozone hole refers to a significant thinning of the ozone layer over Antarctica, which allows more harmful UV radiation to reach the Earth’s surface. Additionally, the persistence of water vapor in the stratosphere beyond what was predicted by models suggests that there is still much to learn about stratospheric circulation processes.

As scientists work to resolve ongoing questions and deepen our understanding of the stratosphere, Schoeberl says the team’s work highlights the critical need for continued research and precise data to tackle the challenges of climate change.

Roland Kays, lead author of a paper on the work, said the study’s goal was to compare the importance of climate versus human factors in where mammals chose to live. To do so, researchers collected data on 25 mammal species from 6,645 locations across the United States. The study is one of the largest camera trap data analyses ever done. The data came largely from Snapshot USA, which is a national mammal camera trap survey conducted with collaborators across the country.

“One of our ideas was that humans may have changed our landscape so much that we have become the primary determinants of which animals live where,” said Kays, who is a research professor at NC State and scientist at the N.C. Museum of Natural Sciences. “What we found was that in fact humans were not the most important. Climate, including temperature and the amount of rainfall, was the most important factor across most of the species we observed.”

However, human activity in the form of large population centers and agriculture was still a significant factor in where mammals chose to live. Some species struggled in the presence of cities and farms, Kays said, but many thrived.

“There are a lot of species that do well when humans are around. The Eastern gray squirrel for instance is the most common squirrel in Raleigh, and it does great around people. But there’s another species called the Eastern fox squirrel, and that one does well around agriculture but not as well around people,” he said. “We can see those differences in many other species. The snowshoe hare does poorly around both people and around agriculture. This study allows us to see the species that are sensitive to our impacts, and which ones benefit.”

This information helped researchers create maps which predict how common various mammals are across the contiguous U.S., which allowed them to separate the country into regions based on what kinds of mammals were common in each. These regions, known as ecoregions, are commonly used when studying plants but have never before been applied to mammal populations.

“When you look at something like the Eastern deciduous forest, that is an ecoregion classified by how common a type of tree is,” Kays said. “We’re now able to do that with mammal species and then compare that to the plant ecoregions. What we found was a striking similarity between the two. For instance, in the east where there is more rainfall, you have more plants growing. That lined up with a greater abundance of mammals that we saw in that region as well, because more plants mean more food for those animals to eat.”

The open access paper, “Climate, food and humans predict communities of mammals in the United States” is available to read in Diversity and Distributions. In identifying climate as the number one influence on mammal habitat choice, the study presents a new tool for predicting the impacts of climate change on mammal populations. Rising global temperatures will cause shifts in where animals are able to live, as well as influence precipitation levels and plant growth. Understanding these factors will be important to making sustainable decisions about mammal population management in the future.