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Trees ‘remember’ wetter times − never having known abundant rain could buffer today’s young forests against climate change
In a changing climate, trees exhibit “legacy effects” from past droughts or wet periods. Young trees, adapted to arid conditions, offer hope for future forest resilience amidst escalating climate challenges globally.
Alana Chin, Cal Poly Humboldt ; Janneke Hille Ris Lambers, Swiss Federal Institute of Technology Zurich, and Marcus Schaub, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL)
What does the future hold for forests in a warmer, drier world? Over the past 25 years, trees have been dying due to effects of climate change around the world. In Africa, Asia, North America, South America and Europe, drought stress amplified by heat is killing trees that have survived for centuries.
Old trees may have grown through entire millennia that were wetter than the past 20 years. We are scientists who study forest dynamics, plant ecology and plant physiology. In a recent study, we found that trees can remember times when water was plentiful and that this memory continues to shape their growth for many years after wet phases end.
This research makes us optimistic that young trees of today, which have never known 20th-century rainfall, have not shaped their structure around water abundance and thus may be better equipped to survive in a chronically dry world.
What if we water the forest?
This study built on nearly 20 years of forest research in response to early warning signs of forest loss in the 1990s in the dry Rhône River Valley of the Swiss Alps. At that time, scientists observed that Scots pine trees that had stood for around 100 years were declining and dying. They wondered whether drought or other climate factors were driving this loss.
To tackle this question, researchers at the Swiss Federal Institute for Forest, Snow and Landscape Research designed an ecological experiment. To understand the impacts of drought, they would irrigate a mature forest, doubling natural summertime rainfall, and then compare how these water-rich trees fared in comparison with those receiving only natural precipitation.
The Pfynwald experiment, launched in 2003, has shown that trees survived at higher rates in irrigated plots. After 17 years of irrigation, the team found that irrigation didn’t just help trees survive dry phases – it also increased their growth rates. https://www.youtube.com/embed/OA7A-xWhDeo?wmode=transparent&start=0 Tree physiologist Leonie Schönbeck conducts research at Pfynwald, a natural reserve in southern Switzerland, to learn how trees take up and store energy and use their reserves to recover from drought.
Legacy effects are forests’ memories
Trees experiencing drought alter their leaves, wood and roots in ways that prime them for continued dry conditions. Wood under drought might have smaller cells that are less vulnerable to future damage, and roots might increase relative to leaf area. These structural changes persist after the drought has passed and continue to influence the tree’s growth and ability to tolerate stress for many years.
Known as “legacy effects,” these lingering post-drought impacts represent an ecological memory of past climatic conditions at the tree and forest level. Knowing that trees hold a persistent memory of past dry phases, researchers wondered whether they might also show structural changes in response to past wet periods.
Eleven years after summertime irrigation started in Pfynwald, scientists stopped irrigating half of each plot in 2013 to address this question. The formerly irrigated trees, which at this point were about 120 years old, had experienced a lasting period of irrigation – but now those times of plenty were over.
Would the trees remember? A decade later, we found out.
Trees, trains and particle accelerators
On an early March morning in 2023, two of us (Alana Chin and Marcus Schaub) met at Pfynwald to collect very fresh leaf and twig samples so that we and colleagues could look inside to search for signs of lasting effects of past water richness.
At the site, we climbed canopy access towers to collect newly grown treetop leaves and twigs from control trees that had never been irrigated; trees that had been irrigated every summer since 2003; and formerly irrigated trees that had not received irrigation water since 2013.
We took our samples to the Swiss Light Source, an intensely powerful synchrotron – a type of particle accelerator that produces the world’s most intense beams of light. This facility is the home of the TOMCAT, an extremely high-resolution X-ray that allowed us to look inside our leaves and twigs without disturbing their structure.
Scanning our samples took all night, but when we stumbled out of the building, we had images capturing every cell in exquisite detail.
The memory of water
We found that the new leaves of once-irrigated trees were different from both continually watered trees and never-watered control trees. Leaves carry out photosynthesis that fuels a tree’s survival and growth. Inside them, we could see the legacy of past water abundance, written in the size, shape and arrangement of cells.
Reading this cellular signature, we observed that, at the expense of structures promoting productivity, formerly irrigated trees showed every sign of chronic water stress – even more so than never-irrigated trees. In their anatomy, we saw why these trees that had it easy for 11 wet years were now growing slowly.
Every cell in a leaf comes with a trade-off. Trees must balance investments in rapid photosynthesis with others that promote leaf survival. Rather than building the cells used to harvest sunlight and ship sugar to the rest of the tree, leaves on the trees that had been irrigated showed every indication of drought stress we could think to measure.
After receiving extra water for an 11-year stretch and then losing it, the trees were producing new, tiny leaves that invested mostly in their own survival. The leaves were structured to protect themselves from insects and drought and to store water reserves. Compared with leaves on trees that had never known irrigation, these looked as though they were in the middle of the drought of the century.
While this memory of water might seem negative, it likely once helped trees “learn” from past conditions to survive in variable environments. The formerly irrigated trees did not know that humans had played a trick on them. Like trees experiencing climate change, they had no way of knowing that the water was not coming back.
When trees experience a drought event, recovery can mean reaching a “new normal” state, in which they are prepared to survive the next drought, with smaller, less vulnerable cells and increased energy reserves to ‘save up’ for future dry periods. They may have deeper roots or a smaller pool of leaves to support, helping them prepare for an unstable environment.
We wanted to know whether the same was true of trees that had experienced water abundance. Were they waiting in distress for the water to return?
Hard times may make tough trees
In some temperate forests, like the ones we studied in Switzerland, old trees once knew levels of water abundance that now are gone, thanks to climate change. That past abundance may have locked into place structural and epigenetic changes in the trees that are mismatched to today’s drier world. If this is true, then some of today’s devastating global tree mortality events may be, in part, due to the legacy effects of past water abundance.
In most of the world’s temperate forests, however, the current cohort of young forest trees – those sprouting in the past 15 to 20 years – has managed to establish itself under conditions that once would have been considered chronic drought. Those young trees, which have survived an endless dry period, will form the forests of the future.
In all, our observations in Pfynwald have provided us some room for hope that young trees currently taking their place in many forests worldwide may be better prepared to cope with the world as humans have shaped it. Climate shifts in recent decades have primed them for hard times, without the lingering memory of water.
Alana Chin, Assistant Professor of Plant Physiology, Cal Poly Humboldt ; Janneke Hille Ris Lambers, Professor of Environmental Systems Science, Swiss Federal Institute of Technology Zurich, and Marcus Schaub, Group Leader, Forest Dynamics and Ecophysiology, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL)
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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health and wellness
Heat waves can leave homes dangerously hot – even for young, healthy adults
Heat waves can turn homes into dangerous heat traps—especially during blackouts or in houses without AC—pushing indoor temperatures and humidity into lethal territory even for young, healthy adults, not just the elderly.
Heat waves can leave homes dangerously hot – even for young, healthy adults
Zoltan Nagy, Eindhoven University of Technology
Most people know that heat waves can be dangerous, but what they may not realize is that the heat indoors can be much worse than outdoors.
When the power goes out and air conditioning stops, or in homes without cooling, a house starts to function like a greenhouse during a heat wave. Heat enters through windows and walls and has nowhere to go. Air stagnates.
Within hours, indoor temperatures can climb well above what the thermometer shows outside, especially on upper floors and in rooms with south-facing windows. Over longer periods, especially if temperatures don’t cool off overnight, conditions can become lethal.
Most heat-related deaths occur indoors. When a heat dome sent temperatures soaring in the Pacific Northwest in 2021, 98% of the more than 600 deaths in British Columbia happened inside homes. Washington and Oregon also saw high numbers of deaths in homes that lacked air conditioning.
In Europe, where only 1 in 10 households have air conditioning, heat waves killed an estimated 60,000 people in 2022 and 47,000 in 2023, largely inside buildings never designed for these temperatures.
People of all ages are at risk in heat waves like these. I spent eight years at the University of Texas at Austin studying how buildings respond to extreme heat. In a recent study, my team assessed the heat risk in every single-family home in Austin.
We found that even younger, healthy adults face far more risk than they realize.
How hot is too hot for a human body?
Your body maintains a core temperature of about 98.6 degrees Fahrenheit (37 degrees Celsius). To cool down, it pushes blood to the skin and sweats. But when air temperature is high, that convective cooling weakens. When humidity is also high, sweat cannot evaporate.
If the body has no way to release heat, core temperature rises. If the core temperature increases past about 104 F (40 C), the body’s thermoregulation starts to fail. Past 109 F (42.8 C), death becomes likely.
What makes indoor heat especially dangerous is that it does not let up at night in homes that lack air conditioning. Outdoor temperatures typically drop after sunset, and someone outside can get a few hours of recovery. But a poorly insulated home that has been absorbing heat all day releases that heat slowly, keeping indoor temperatures elevated through the night. A person inside the home never gets a break.
After two or three nights of this, even healthy people start to be at serious risk for heat-related illnesses.
Why homes heat up more than people expect
People tend to underestimate indoor heat for a few reasons.
One is that the thermostat typically sits on one wall in one room. It does not tell what the temperature is in an upstairs bedroom or near a sun-facing window. In older, underinsulated homes, the actual felt temperature can exceed 90 F (32.2 C) even when a thermostat reads 75 F (23.9 C). The hot walls, ceilings and windows can radiate heat directly onto your body.
Another reason is that people assume all homes respond to heat the same way. However, a newer home with double-pane windows and good insulation acts like a thermos, keeping heat out for a longer time. An older home with single-pane windows and cracks in the walls heats up fast.
Two houses on the same street, exposed to the same outdoor conditions, can have completely different temperatures inside. And in a blackout, where neither home has cooling, those differences can become a matter of life and death.
What we found in Austin
Our study combined two datasets. From Austin’s tax appraisal records, we pulled basic property information, such as the year the home was built, the size and the number of stories for each of the city’s 213,000 single-family homes. We then matched each home to the most similar energy simulation models in a U.S. Department of Energy database that contains thousands of detailed, physics-based building energy models representing the U.S. residential building stock.
Using those models, we simulated each building’s indoor temperatures over time during a three-day heat wave and power outage with outdoor temperatures above 110 F (43 C).
We found that 85% of homes got hot enough to pose a significant risk of death for an elderly occupant. But what surprised us was the risk to younger people.
Under today’s climate conditions in Austin, about 15% of homes already have the potential to get hot enough without air conditioning to pose serious heat risks to healthy adults. Under future warming scenarios, that number jumps to as high as 65% if average summer highs reach 104 F (40 C). Further, climate projections for Austin show that heat waves will double in frequency by the end of the century.
We found three types of buildings and accompanying risks:
- Resilient homes, which are newer and well insulated, tended to have temperature and humidity conditions that would be survivable for an elderly occupant throughout the simulated heat wave with blackout.
- Critical-risk buildings, which are mostly older homes, became dangerous almost immediately.
- And then there was the middle group – homes where temperatures rose slowly during the simulated blackout, day by day, possibly giving occupants a false sense of security until it was too late.
Texas has already seen conditions like our case study’s – a heat wave paired with a power outage. In 2024, a derecho knocked out power for nearly 900,000 Houston households while the heat index climbed to 100 F (37.8 C). Seven weeks later, Hurricane Beryl cut power to 2.6 million homes, leaving them without power for over three days, with temperatures over 90 F (32.2 C).
What you can do to stay safe
If you can’t get cooling at home, there are steps you can take that can help.
Move to the lowest floor of your home, where it will be coolest. Close the blinds and curtains on sun-facing windows. Drink water constantly to stay hydrated, which is essential for regulating body temperature.
If you’re facing a blackout, be sure to also check on elderly neighbors, especially those living alone. You can also try to find a public cooling center; many cities now open them during heat emergencies.
Longer term, upgrades such as reflective window film, attic insulation and lighter-colored roofing can reduce how much a home heats up. After the 2021 heat dome, British Columbia’s coroner recommended updating building codes to address heat.
Our own findings point in the same direction: We propose that new homes should be required by building codes to maintain conditions in which at least light physical activity remains possible for all occupants for at least 72 hours during a power outage.
As summers get hotter with climate change and blackouts become more frequent, the risks of people suffering heat illnesses will only continue to rise.
Zoltan Nagy, Professor of Building Services, Eindhoven University of Technology
Heat waves can leave homes dangerously hot – even for young, healthy adults
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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How to Protect Yourself from a Smartphone Scam
(Feature Impact) The first sign is unexpectedly losing access to your cell phone. Soon after, when you connect to Wi-Fi, the gravity of the situation sinks in: a criminal has gained access to your cell phone number and is trying to siphon money from your credit cards and bank accounts.
The scam is called SIM swapping, or SIM hijacking, and it’s a concern for law enforcement in the United States and abroad as more than 5,000 people have reported SIM swapping scams to the FBI since 2022. Older adults, caregivers and families can benefit from understanding the warning signs of SIM swapping and taking simple security steps to prevent it from happening.
How SIM swapping works
A SIM card, or its digital version known as an eSIM, helps connect a phone number to a carrier network. In a SIM swapping scam, a criminal collects basic information about their victim, such as their name, birthdate and address, to try to move the victim’s phone number to a SIM card or eSIM profile the criminal controls.
Once complete, the scammer gains access to accounts you may be logged into on your phone, such as bank accounts or credit card apps, without touching your phone or being near you.
How to protect yourself from SIM swapping scams
Preparation is the best protection against SIM swapping. Cell phone users should use strong, unique passwords for each online account – password managers are a helpful tool in creating complex and randomized passwords. Use two-factor authentication where it’s offered; this adds an extra layer of security when accessing sensitive accounts.
Next, consumers should protect personal information they share online, whether on social media or in texts or emails asking for identifying data, such as PIN numbers, birthdates or one-time security codes. Be wary of anyone pushing you to share personal information, particularly if they’re pushy with their request or make it sound urgent.
Check your mobile carrier to see if it offers SIM protection. For example, Verizon customers can toggle on a protection feature on the carrier’s website or app to lock lines on their account to help prevent SIM changes.
If you get an unprompted notification that your SIM has been changed, or otherwise suspect you’ve been targeted in a SIM swapping scam, contact your banks immediately and have them freeze your accounts, including ones the criminals may not have targeted yet. Next, work with your cell phone provider to help regain access to your mobile device. If you’re able, share as much information as possible with law enforcement so they can investigate, or at least document trends, in how often this scam occurs.
To find more advice to protect against smartphone scams, visit Verizon.com.
Photo courtesy of Shutterstock
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Supreme Court rules against trans girls participating in single‑sex sports, but leaves open larger questions of trans rights
The U.S. Supreme Court ruled on June 30, 2026, that West Virginia and Idaho did not violate the Constitution by preventing transgender students from joining female sports teams, and that states can restrict who participates on women’s and girls sports teams based on a student’s sex assigned at birth.
Marie-Amelie George, Wake Forest University
The U.S. Supreme Court ruled on June 30, 2026, that West Virginia and Idaho did not violate the Constitution by preventing transgender students from joining female sports teams, and that states can restrict who participates on women’s and girls sports teams based on a student’s sex assigned at birth.
This ruling, focused squarely on transgender students participating on single-sex sports teams, does not resolve other major questions that are important to trans rights. These issues include what bathrooms transgender or nonbinary students can use at school, as well as whether transgender individuals can update their names and gender markers on identity documents.
The court folded two related cases that address sports team participation at the middle, high school and college levels – Little v. Hecox and West Virginia v. B.P.J. – into one single decision that resolved both. The justices ruled 6-3 on the cases.
This ruling backs 25 other states that, over the past few years, have passed new laws restricting transgender students from participating on female sports teams.
Twenty-one states also have some sort of restriction on transgender and nonbinary students using school bathrooms designated by sex.
As a legal scholar and expert on LGBTQ+ rights, I believe that based on the court’s reasoning, it is likely that the conservative majority on the court would uphold states’ right to restrict school bathroom use based on sex assigned at birth. However, this ruling leaves bigger questions regarding transgender students’ broader rights in school, at work and elsewhere unanswered.
A political flash point
There were estimated to be fewer than 10 transgender athletes who participated in collegiate athletics in 2024.
But the issue of transgender students participating on sports teams is a hot-button issue for the Trump administration and Republicans, who argue that transgender female students have a biological advantage in competitive sports over athletes assigned female at birth.
The issue is nuanced and depends on factors including the athletes’ age and whether they have undergone gender-affirming hormonal therapy.
Some recent research shows that transgender female athletes who have undergone gender affirming hormone therapy have a comparable level of strength to cisgender female athletes.
What the rulings covered
At issue in these two Supreme Court cases were what protections Title IX – which bars sex-based discrimination in education programs and activities that receive federal funding – as well as the equal protection clause of the 14th Amendment gave transgender students.
Little v. Hecox challenged Idaho’s 2020 law that allows only students whose sex was designated female at birth to participate on girls and women’s school sports team.
Lindsay Hecox, a transgender female student at Boise State University, alongside a cisgender student, filed a lawsuit against the state in 2020. Hecox, now 24, could not try out for the school’s track and cross country team because of the law. She instead ran at the club level.
In West Virginia v. B.P.J., a transgender middle school student athlete named Becky Pepper-Jackson similarly sued the state so she could continue participating in track and field. Pepper-Jackson won a state title in girls shot put in May 2026.
The state’s 2021 Save Women’s Sports Act requires public middle schools, high schools and colleges to designate all school athletic teams by biological sex.
Understanding Title IX and how it applies
The Supreme Court determined that states are permitted to restrict sports team participation under Title IX and its regulations, which explicitly permit schools to have separate male and female sports teams.
The opinion started by emphasizing there are “enduring” physical differences between males and females, and that if there were unified sports teams, females could be at a disadvantage.
“Separate sports teams for biological males and biological females are reasonable: Given the inherent physical differences between the sexes, allowing only biological females to play on women’s and girls’ teams can reduce the risk of physical injury and ensure fair competition,” the court ruled in its opinion on West Virginia v. B.P.J., authored by Justice Brett Kavanaugh. Chief Justice John Roberts and Justices Samuel Alito, Clarence Thomas, Neil Gorsuch and Amy Coney Barrett joined the ruling.
Pepper-Jackson argued that this part of Title IX did not have relevance to her case because she had taken puberty blockers and never gone through male puberty.
As a result, she argued, she did not have heightened levels of testosterone or other physical differences that could raise the concern of a competitive advantage over cis female students in sports. She also posed no physical safety concerns for her teammates.
The court’s majority rejected this argument, saying that the Title IX regulations did not speak to this issue. The court recognized that although the laws might produce unfair results for someone like Pepper-Jackson, this did not make the restrictions improper.
The court added that Pepper-Jackson and other students in her position need to take up their concerns with state legislatures.
The court’s liberal wing – Justices Sonia Sotomayor, Elena Kagan and Ketanji Brown Jackson – agreed with the conservative majority that the laws did not violate Title IX.
The role of the equal protection clause
The court also addressed the equal protection clause of the U.S. Constitution, which says that the government must apply its laws fairly and cannot treat people differently without a valid reason.
The court’s conservative majority ruled that the laws distinguished based on sex, and as a result they scrutinized the laws more carefully. However, the court concluded that the athletic restrictions nevertheless passed constitutional muster.
Here, too, the court’s majority cited the interests of safety and competitive fairness as important justifications for the laws.
The liberal justices disagreed with their colleagues’ analysis. In their view, the laws were too broad to satisfy the Constitution, because they banned transgender girls who had never experienced male puberty from female sports teams.
A side step
The decision is a narrow one. The court went to great lengths to emphasize that it was focused on sports, and that the court was not being asked about transgender people’s rights more broadly.
In the court’s telling, sports are unique because competition depends on the physiology and physical differences between those assigned male and female at birth. That is important, because there are few circumstances in which the physical differences between males and females continue to be relevant.
In the past, many occupations and schools were sex-segregated. Today, bathrooms, school sports teams, changing facilities, some college residence halls, juvenile detention centers and prisons are among the last places that remain segregated by sex.
Moreover, the court avoided ruling on the constitutional standard that should apply when transgender people are discriminated against. Under constitutional doctrine, courts will more closely scrutinize laws that discriminate against historically powerless minority groups, such as people of color and women.
One of the open questions in transgender rights litigation is whether transgender people qualify for that more searching review.
This case did not resolve that issue.
The court’s narrow ruling on transgender athletes ultimately did not resolve other key issues for transgender rights, which the court will likely be asked to address at a later date.
Marie-Amelie George, Associate Professor of Law, Wake Forest University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
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