One of the method’s applications is to give a more complete sense of human ancestry, says Gideon Bradburd, U-M professor of ecology and evolutionary biology. For example, when you send your DNA off for a personalized ancestry report, the report you get back is only a very small view of your family tree pinned in a specific point and space in time.

These types of genetic reports reflect the amount of a person’s genome that they’ve inherited from individuals living in a specific area at a specific point in the past. If your ancestry report says that you’re 50% Irish, that means you have a lot of second through fourth cousins who currently live in Ireland, says Bradburd. But in reality, your family tree is much more like a movie than this snapshot.

The statistical method developed by Bradburd and fellow U-M researchers Michael Grundler and Jonathan Terhorst can give people a “movie” version of their ancestry, showing where their ancestors originated and how they moved across the globe. The method uses modern genetic sequence samples, estimates all of the locations of an individual’s genetic ancestors, identifies the average location of those individuals based on assumptions about how people move, and tracks it back over centuries.

The researchers’ method can be used for more than tracing human ancestry. It can also be used to track the emergence of viruses, the divergence of animal populations and other genealogical tracking. Their results are published in the journal Science.

“There’s ways in which consumer ancestry reports are interesting, and certainly it’s powerful to learn about your history, especially for folks who’ve been adopted or orphaned or are disconnected from their family,” Bradburd said. “But there are other ways in which these ancestry reports can be really problematic. They really reify notions of the biological essentialism of race because they’re presenting these categories of Irish, for example, as if they’re ideals, that they’re real and unchanging through time.”

But researchers know this isn’t the case. A field, forged by Nobel Prize-winning geneticist Svante Pääbo, developed the tools to genotype ancient DNA. This allows researchers to trace waves of human populations as they spread throughout the world — particularly in Eurasia, where most of this type of genetic sequencing has been happening, Bradburd says. This has allowed researchers to see how human groups enter and leave geographic regions through time.

“Because the genetic flavor of a location changes so much through time, we know it’s meaningless to say, ‘This is what it means to be Irish,'” Bradburd said. “It’s not just that being ‘genetically Irish’ doesn’t mean anything; it also means that you are everything.”

Bradburd points to a thought experiment in human biology: imagine two biological parents and four biological grandparents. This doubles every generation, and it only has to double a relatively small number of generations before there are more people in that direct lineage than there have ever been humans alive on Earth.

This also means that you don’t have to go very far back in time to discover that many people share many ancestors.

“Because our pedigrees explode so quickly, they also must collapse in the same sense that you and I must share many, many relatives at many points back in time, and that’s true for every person alive on Earth,” Bradburd said. “We’re all extraordinarily closely related to each other.”

The ancestry reports are accurate, Bradburd said, but specifically when they are tied to a time period.

“The ancestry reports aren’t wrong, but they’re leaving out a very important component, which is the ‘when’ you have Irish ancestry,” Bradburd said. “Because we know the modern human lineage arose in Africa, it is as accurate to say that you have 100% African ancestry at a deeper time horizon.”

The statistical method, called Gaia (geographic ancestry inference algorithm), starts by making a very simple assumption about how individuals move: that typically they move locally. The method combines that assumption with the location of modern-day individuals and a genetic structure that relates them called the ancestral recombination graph.

With those two pieces of information and the simple model of how individuals move, the researchers can compute the “most parsimonious locations of ancestors,” Bradburd says. The researchers then can propagate that information back through the past.

Bradburd’s work is answering a call from the National Academy of Sciences, urging researchers working on human population genetics to move away from race-based labels. While the sociological realities of race are undeniable, racial categories do not make good predictions about genetic variation, he says.

Because of the disconnect between race and genetics, racial labels can often be imprecise: two people might share the same label, but be much more closely or less closely related to each other. In addition, because the genetics in a certain geographic area can shift so much over time, geographic and national labels can also be misleading, Bradburd says.

“Saying you’re ‘genetically Irish’ makes it seem like ‘Irish’ has always meant the same thing, and genetically we know that is not true and also that anyone who is Irish — meaning they inherited parts of their genome from people who lived in Ireland — is only Irish with respect to a specific time horizon,” he said. “That these race labels gloss over both of these important pieces of information is a big loss of specificity and also poses a very real danger to the weaponization of science for political means.”

The method Bradburd’s team developed can be applied to systems other than human genetics. Researchers can use this method to look at the genetic distribution of the organisms they study. Researchers can also use this method to learn about the migration of organisms — human and otherwise, Bradburd says.

For example, researchers have been able to look at measures of genetic similarity of population between two locations and infer that they are more or less closely connected by migration, or more or less isolated from each other. But this tool allows researchers to pin a timeline on when these movements happened.

And this tool can apply in this case to more than tracing human genetics — it can be used to help determine when a disease might have emerged from a specific region of the world, for example. The U-M group is working with researchers in Australia to learn how mosquitoes colonized islands of the South Pacific, and with researchers in Michigan and Ohio to understand the history and dispersal of the Massasauga rattlesnake.

“It’s one of the things I’m quite excited about with this — you can use this method to identify dispersal patterns through time and between specific locations,” Bradburd said. “Notions of ancestry don’t have to be static. Instead, you should think of them as being dynamic, and interesting and understandable more as a movie than as a picture.”

The discrepancy between model results and observed cooling, Stanford University scientists have now found, comes down mainly to missing meltwater and underestimated rainfall.

“We found that the Southern Ocean cooling trend is actually a response to global warming, which accelerates ice sheet melting and local precipitation,” said Earle Wilson, an assistant professor of Earth system science in the Stanford Doerr School of Sustainability and senior author of the March 27 study in Geophysical Research Letters.

As rising temperatures melt Antarctica’s ice sheet and cause more precipitation, the Southern Ocean’s upper layer is growing less salty — and thus, less dense. This creates a lid that limits the exchange of cool surface waters with warmer waters below. “The fresher you make that surface layer, the harder it is to mix warm water up,” Wilson explained.

But this freshening is not fully represented in state-of-the-art climate models — a flaw that scientists have long recognized as a major source of uncertainty in projections of future sea level rise. “The impact of glacial meltwater on ocean circulation is completely missing from most climate models,” Wilson said.

Reconciling global discrepancies

The mismatch between observed and simulated sea surface temperatures around Antarctica is part of a larger challenge for scientists and governments seeking to prepare for climate impacts. Global climate models generally do not accurately simulate the cooling observed over the past 40 years in the Southern Ocean and the eastern Pacific around the equator or the intensity of the warming observed in the Indian and western Pacific Oceans. There is also a discrepancy between simulations and the observed frequency of La Niña weather conditions, defined by the eastern Pacific being colder than average.

Warming events in the Southern Ocean over roughly the past eight years have somewhat diminished the 40-year-long cooling trend. But if sea surface temperature trends around the globe continue to resemble patterns that have emerged in recent decades, rather than shifting toward the patterns predicted in simulations, it would change scientists’ expectations for some near-term impacts from climate change. “Our results may help reconcile these global discrepancies,” Wilson said.

Oceans globally have absorbed more than a quarter of the carbon dioxide emitted by human activities and more than 90% of the excess heat trapped in our climate system by greenhouse gases. “The Southern Ocean is one of the primary places that happens,” said lead study author Zachary Kaufman, a postdoctoral scholar in Earth system science.

As a result, the Southern Ocean has an outsized influence on global sea level rise, ocean heat uptake, and carbon sequestration. Its surface temperatures affect El Niño and La Niña weather patterns, which influence rainfall as far away as California.

A surprising discovery

To understand the physical mechanism for Southern Ocean cooling — and enable more reliable projections of its future impacts on Earth’s climate system — Wilson and Kaufman set out to determine how much sea surface temperatures around Antarctica in simulations have cooled in response to freshening. “We naively figured it wouldn’t matter exactly where you put the freshwater,” Wilson said.

The researchers were surprised to discover that surface temperatures are much more sensitive to freshwater fluxes concentrated along the coast than those splashing more broadly across the ocean as rain.

“Applying freshwater near the Antarctic margin has a bigger influence on sea ice formation and the seasonal cycle of sea ice extent, which then has downstream impacts on sea surface temperature,” Wilson said. “This was a surprising result that we are eager to explore further in future work.”

Quantifying the effect of missing meltwater

Previous studies have sought to quantify how Antarctic meltwater affects the global climate system by adding some amount of freshwater to a single climate model simulation, in what scientists have dubbed “hosing” experiments. “You get very divergent results, because people set up their experiments slightly differently, and the models are a little different, and it’s unclear if these are really apples-to-apples comparisons,” Wilson explained.

For the new study, the researchers sought to avoid this issue by working with a collection of simulations. Using a new ensemble of coupled climate and ocean models from the recently launched Southern Ocean Freshwater Input from Antarctica (SOFIA) Initiative, as well as an older set of models simulating ocean density and circulation changes, the authors analyzed how much simulated sea surface temperatures changed in response to the actual freshwater inputs between 1990 and 2021.

“There’s been some debate over whether that meltwater is enough over the historical period to really matter,” said Kaufman. “We show that it does.”

With the new method, which incorporates simulations from 17 different climate models, the researchers found missing freshwater explains up to 60% of the mismatch in observed and predicted Southern Ocean surface temperatures between 1990 and 2021.

“We’ve known for some time that ice sheet melting will impact ocean circulation over the next century and beyond,” Wilson said. “Our results provide new evidence that these meltwater trends are already altering ocean dynamics and possibly the global climate.”

Additional co-authors include Yuchen Li, an undergraduate student in the Physics Department in the Stanford School of Humanities and Sciences, Ariaan Purich of Monash University, and Rebecca Beadling of Temple University.

This research was supported by Stanford University, a grant from the NSF Division of Polar Programs, and the Australian Research Council Special Research Initiative for Securing Antarctica’s Environmental Future. Li was supported by the Sustainability, Engineering and Science — Undergraduate Research (SESUR) program in the Stanford Doerr School of Sustainability.

The study, which was published in the Journal of Health Psychology, looked at how patients with Long Covid experience their illness. The study found that many patients feel they have to prove their illness is physical to be taken seriously and, as a result, often reject psychological support, fearing it implies their symptoms are “all in the mind.”

Professor Jane Ogden, co-author of the study from the University of Surrey, said:

“We found that the problem isn’t people with Long Covid refusing help — it’s about the deep need for people to be believed. When a patient feels dismissed, offering psychological support instead of medical care can be misconstrued as insulting.”

According to the Office for National Statistics, there are 1.9 million people who live with Long Covid in the UK. Long Covid symptoms include fatigue, difficulty concentrating, muscle aches and shortness of breath, which persist for many weeks, sometimes months, after the initial Covid-19 infection.

Surrey’s study involved in-depth interviews with 14 people in the UK between the ages of 27 to 63 who had experienced Long Covid symptoms for more than four weeks. The group included 12 women and two men.

Saara Petker, clinical psychologist, co-author of the study and former PhD student at the University of Surrey, said:

“We found that our participants are living a life of constant uncertainty, struggling to find treatment. People told us that they didn’t feel listened to, some said they’d lost trust in doctors, their social circles and even their own bodies because of the whole experience.

“Medical advice is crucial — but psychological support must be offered with care. If it’s seen as replacing medical help, it can feel dismissive.”