The Earth
No, autumn leaves are not changing color later because of climate change
“Have scientists observed any changes in the timing or intensity of leaf color changes?”
Fall foliage on the Danforth Campus of Washington University in St. Louis.
It’s that time of year again. The days are getting shorter, and the nights are cooling down. But when will the natural fireworks display of autumn leaves actually begin this year?
Many people believe that climate change is pushing back the start of fall leaf color to later in the year. The general thinking is that the warmer conditions anticipated under climate change will mean that trees can “hang on” to their green, energy-producing leaves longer. But scientists do not actually see this happening across North American forests, according to an expert at Washington University in St. Louis.
“Warmer temperatures in September and October reduce anthocyanin production in leaves, which could mean that fall colors would become less brilliantly red or purple,” said Susanne S. Renner, honorary professor of biology in Arts & Sciences. “This effect is well documented in certain species, such as sugar maple, where experimental cooling of branches increases anthocyanin concentration and color brilliance. If the first frost comes later than it used to, the brilliant foliage will appear later than it used to.
“However, other factors counteract this. Most important is that trees drop their leaves earlier if they have had a very productive spring and summer. This overrides any delaying effects of a warm fall.
“The end result is that leaves still start to die after about the same amount of time on the tree as they have in years and even decades past,” she said.
In fact, under some scenarios we might even see leaves turning red and yellow earlier. Renner co-authored a 2020 study in the journal Science that showed that increased growing-season productivity drives earlier autumn leaf senescence — the process through which plants break down and reabsorb key nutrients that had been deployed in leaves — in temperate trees.
“If climate warming continues unabated, the situation is likely to change after about 2040, with senescence then starting earlier than it does now,” Renner said.
Here, Renner answers a few additional questions related to autumn leaf color change.
How do temperature and moisture conditions affect leaf color?
Yellow color in fall leaves is due to the retention of carotenoid pigments (xanthophylls) in senescing chloroplasts. Red and purplish color is due to the accumulation of anthocyanins in vacuoles, starting around September.
Rain does not affect these basic processes. Cold temperatures, however, enhance anthocyanin production, as shown experimentally in sugar maple. One can observe this in the sugar maple trees along St. Louis streets, which start turning colors at the very top, where the microclimate is coldest.
How might climate change alter color dynamics?
Because climate warming has resulted in warmer falls, in Canada and North America we are seeing less brilliant fall colors. Color brilliance is hard to quantify, but the effect has been experimentally demonstrated in sugar maple trees.
An interesting confounding factor is cleaner air. Thus, in Europe, atmospheric brightening due to cleaner air since 1983 has led to higher plant photosynthesis in the spring and summer — and earlier leaf senescence (compared with 1950-1982). These data, however, concern the breakdown of chlorophyll, not the production of red or yellow colors.
Will all kinds of trees respond in the same ways?
Absolutely not. Experimental work is revealing great species-specific differences. For example, trees that have nitrogen-fixing symbionts never turn red or yellow. Both pigments help protect leaves against damage from sunlight that is no longer usable for photosynthesis because of the massive degradation of chloroplast proteins in aging leaves. Trees with steady access to nitrogen may not bother with costly anthocyanin, but instead simply drop their leaves while still relatively green.
Are scientists already seeing changes to the timing or intensity of leaf color changes?
Warmer falls reduce the brilliance of red and yellow leaf colors, but brilliance is hard to quantify in long time series for many species. Also, many species simply do not turn red or yellow.
We have a paper under review that analyzes satellite data on “greenness” in Northern Hemisphere forests. We found that across a large majority of forest areas, higher spring and summer temperatures have led to an earlier (!!!) senescence by, on average, about 1.5 days per degree Celsius. Senescence here refers to degradation of chlorophyll or greenness.
Where in the world are autumn leaves most likely to be affected by climate change?
Species that change leaf color to red or yellow are much more frequent in North America than in Europe. With continued climate warming and lack of frost nights in October, colors will be less brilliant, but the onset or dates of color change will not change much because of the counteracting factors that I mentioned earlier. In the more distant future (after about 2040), and with unmitigated climate change, leaf senescence in Northern Hemisphere trees and shrubs will occur ever earlier.
Source: Washington University in St. Louis
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Nature
Sharks and rays leap out of the water for many reasons, including feeding, courtship and communication
Research by A. Peter Klimley on sharks and rays breaching reveals it functions mainly to remove parasites, attract mates, or hunt prey.
A. Peter Klimley, University of California, Davis
Many sharks and rays are known to breach, leaping fully or partly out of the water. In a recent study, colleagues and I reviewed research on breaching and ranked the most commonly hypothesized functions for it.
We found that removal of external parasites was the most frequently proposed explanation, followed by predators chasing their prey; predators concentrating or stunning their prey; males chasing females during courtship; and animals fleeing predators, such as a ray escaping from a hammerhead shark in shallow water.
We found that the highest percentage of breaches, measured by the number of studies that described it, occurred in manta rays and devil rays, followed by basking sharks and then by eagle rays and cownose rays. However, many other species of sharks, as well as sawfishes and stingrays, also perform this behavior. https://www.youtube.com/embed/wXkMqk8mwjs?wmode=transparent&start=0 A breaching white shark surprises researchers off Cape Cod, Massachusetts.
Why it matters
It takes a lot of energy for a shark or ray to leap out of the water – especially a massive creature like a basking shark, which can grow up to 40 feet (12 meters) and weigh up to 5 tons (4.5 tonnes). Since the animal could use that energy for feeding or mating, breaching must serve some useful purpose.
Sharks that have been observed breaching include fast-swimming predatory species such as blacktip sharks and blue sharks. White sharks have been seen breaching while capturing seals in waters off South Africa and around the Farallon Islands off central California.
However, basking sharks – enormous, slow-swimming sharks that feed by filtering tiny plankton from seawater – also breach. So do many ray species, such as manta rays, which also are primarily filter feeders. This suggests that breaching likely serves different functions among different types of sharks and rays.
The most commonly proposed explanation for breaching in planktivores, like basking sharks and most rays, is that it helps dislodge parasites attached to their bodies. Basking sharks are known to host parasites, including common remoras and sea lampreys. The presence of fresh wounds on basking sharks that match the shape and size of a lamprey’s mouth suggests that breaching has torn the lampreys off the sharks’ bodies. https://www.youtube.com/embed/zsC61g36EqM?wmode=transparent&start=0 Basking sharks are filter feeders that live on plankton. They may breach to rid their bodies of parasites.
Other species may breach to communicate. For example, white sharks propelling themselves out of the water near the Farallon Islands may do so to deter other sharks from feeding upon the carcass of a seal.
Researchers have seen large groups of mantas and devil rays jumping together among dense schools of plankton – presumably to concentrate or stun the plankton so the rays can more easily scoop them up. Scientists have also suggested that planktivorous sharks and rays may breach to clear the prey-filtering structures in their gills.
Understanding more clearly when and how different types of sharks and rays breach can provide insights into these animals’ life habits, and into their interactions with their own species and competitors.
How we did our work
I worked with marine scientists Tobey Curtis, Emmett Johnston, Alison Kock and Guy Stevens. Across our various projects, we have seen breaching in bull sharks in Florida, basking sharks in Ireland, white sharks in South Africa and central California, and manta rays in the Maldives. Each of us has proposed different explanations for why the animals did it.
We reviewed scientific studies and video footage to see what species had been observed to breach, under what conditions, and the functions that other researchers had proposed for them doing so. This included information gathered from data logging tags attached to sharks and rays, digital photography, and imagery from underwater and aerial drones.
Our review proposes further studies that could provide more information about breaching in different species. For example, attaching data loggers to individual animals would help scientists measure how quickly a shark or ray accelerates as it propels itself out of the water.
Experiments in aquarium tanks could provide more insight into why the animals breach. For example, scientists could add remoras to a tank containing bull sharks, which can live in an aquarium environment, and observe how the sharks respond when remoras attach themselves to the sharks’ bodies.
In the field, researchers could play audio recordings of splashes from breaches to elicit withdrawal or attraction responses from sharks tagged with ultrasonic transmitters. There remains much to learn about why these animals spend precious energy jumping out of the water.
The Research Brief is a short take on interesting academic work.
A. Peter Klimley, Adjunct Associate Professor of Wildlife, Fish, & Conservation Biology, University of California, Davis
This article is republished from The Conversation under a Creative Commons license. Read the original article.
The science section of our news blog STM Daily News provides readers with captivating and up-to-date information on the latest scientific discoveries, breakthroughs, and innovations across various fields. We offer engaging and accessible content, ensuring that readers with different levels of scientific knowledge can stay informed. Whether it’s exploring advancements in medicine, astronomy, technology, or environmental sciences, our science section strives to shed light on the intriguing world of scientific exploration and its profound impact on our daily lives. From thought-provoking articles to informative interviews with experts in the field, STM Daily News Science offers a harmonious blend of factual reporting, analysis, and exploration, making it a go-to source for science enthusiasts and curious minds alike. https://stmdailynews.com/category/science/
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The Earth
Rare Florida fossil finally ends debate about how porcupine jaws and tails evolved
A nearly complete fossil of an extinct North American porcupine helped resolve a debate on its ancestors’ evolution, revealing distinct traits developed recently.
Natasha S. Vitek, Stony Brook University (The State University of New York)
A rare, nearly complete fossil of an extinct North American porcupine helped me and my colleagues solve a decades-long debate about how the modern North American porcupine evolved from its ancestors.
Published in Current Biology, our paper argues that North American porcupine ancestors may well date back 10 million years, but they wouldn’t be recognizable until about 8 million years later.
By comparing the bone structure of porcupines across North America and South America, we determined that for those 8 million years, North American porcupines unexpectedly still looked like their cousins, the Neotropical porcupines, which live across tropical Central America and South America today.
Our findings detail the North American porcupine’s evolutionary path from South America – and also solve the mystery of why it’s been so difficult to find its ancestors.
I’m a paleontologist who researches the fossilized bones and teeth of extinct animals. With museum curator Jon Bloch, I created a class where we analyzed bone structure to reach the conclusions of our study.
Why it matters
The modern North American porcupine is distinctive among its spiky relatives. It has a short tail, a jaw that can scrape bark from trees and weighs between 10 and 25 pounds (4.5 and 11.3 kilograms).
While clearly related, Neotropical porcupines look different. They have long, grasping tails, weaker jaws and weigh between 1.5 and 10 pounds (0.68 and 4.5 kilograms).
DNA analyses of modern animals estimate that these two groups separated about 10 million years ago.
This is where the mystery comes in. Fossils of the North American porcupine are all younger than 1.8 million years old. In other words, roughly 8.2 million years’ worth of fossils of North American porcupine were missing.
All researchers had were bits of jaws and tails that looked like they belonged to Neotropical porcupines.
Two competing hypotheses could explain the similarity.
Some scientists argued that the jaw and tail fossils of early ancestors of North American porcupines should look more like their modern descendants. Researchers who backed this idea suggested that the fossil record was incomplete for some unexplained reason, but that it was still possible that fossils that supported their hypothesis may eventually turn up.
Other scientists suggested that all early ancestral porcupines might have had jaws and tails similar to today’s Neotropical porcupines. North American porcupine ancestors might be hidden in the existing fossil record because – based on jaws and tails alone – they look identical to Neotropical porcupine ancestors. Only younger fossils would show distinctive traits because that’s when those traits appeared.
This debate went on for decades. It was impossible to solve with the available fossils.
How we did our work
Then researchers from the Florida Museum of Natural History unearthed a 2 million-year-old nearly complete skeleton of a porcupine in north-central Florida in 2005.
The fossil had a long tail and no bark-gnawing jaw, similar to Neotropical porcupines. But it also had dozens more bones that we could use to resolve relationships.
Collecting that evidence required combing through all the bones, looking for hundreds of minute details – like the shapes of ridges or patterns of boundaries on bones – and comparing these details with skeletons of modern North American and Neotropical porcupines. Bloch and I created a course in which students each took on one portion of the project.
Together, we came up with a list of nearly 150 informative details. Even though the specimen had a few traits similar to Neotropical porcupines, more evidence supported the idea that this fossil was a closer relative of North American porcupines.
Since this porcupine had a jaw and tail like its Neotropical cousins, it’s likely that most older relatives of the North American porcupine were also missing the distinctive traits of their modern descendants.
In other words, the solution to the mystery is that the fossil record for North American porcupines appeared young because the reinforced jaw and shorter tail evolved relatively recently. Porcupines looked different than what we expected for much of their 10 million years of ancestry.
The Research Brief is a short take on interesting academic work.
Natasha S. Vitek, Assistant Professor of Ecology and Evolution, Stony Brook University (The State University of New York)
This article is republished from The Conversation under a Creative Commons license. Read the original article.
The science section of our news blog STM Daily News provides readers with captivating and up-to-date information on the latest scientific discoveries, breakthroughs, and innovations across various fields. We offer engaging and accessible content, ensuring that readers with different levels of scientific knowledge can stay informed. Whether it’s exploring advancements in medicine, astronomy, technology, or environmental sciences, our science section strives to shed light on the intriguing world of scientific exploration and its profound impact on our daily lives. From thought-provoking articles to informative interviews with experts in the field, STM Daily News Science offers a harmonious blend of factual reporting, analysis, and exploration, making it a go-to source for science enthusiasts and curious minds alike. https://stmdailynews.com/category/science/
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Tech
A third of the world’s population lacks internet connectivity − airborne communications stations could change that
Mohamed-Slim Alouini, King Abdullah University of Science and Technology and Mariette DiChristina, Boston University
About one-third of the global population, around 3 billion people, don’t have access to the internet or have poor connections because of infrastructure limitations, economic disparities and geographic isolation.
Today’s satellites and ground-based networks leave communications gaps where, because of geography, setting up traditional ground-based communications equipment would be too expensive.
High-altitude platform stations – telecommunications equipment positioned high in the air, on uncrewed balloons, airships, gliders and airplanes – could increase social and economic equality by filling internet connectivity gaps in ground and satellite coverage. This could allow more people to participate fully in the digital age.
One of us, Mohamed-Slim Alouini, is an electrical engineer who contributed to an experiment that showed it is possible to provide high data rates and ubiquitous 5G coverage from the stratosphere. The stratosphere is the second lowest layer of the atmosphere, ranging from 4 to 30 miles above the Earth. Commercial planes usually fly in the lower part of the stratosphere. The experiment measured signals between platform stations and users on the ground in three scenarios: a person staying in one place, a person driving a car and a person operating a boat.
My colleagues measured how strong the signal is in relation to interference and background noise levels. This is one of the measures of network reliability. The results showed that the platform stations can support high-data-rate applications such as streaming 4K resolution videos and can cover 15 to 20 times the area of standard terrestrial towers.
Early attempts by Facebook and Google to commercially deploy platform stations were unsuccessful. But recent investments, technological improvements and interest from traditional aviation companies and specialized aerospace startups may change the equation.
The goal is global connectivity, a cause that brought the platform stations idea recognition in the World Economic Forum’s 2024 Top 10 Emerging Technologies report. The international industry initiative HAPS Alliance, which includes academic partners, is also pushing toward that goal.
Fast, cost effective, flexible
Platform stations would be faster, more cost effective and more flexible than satellite-based systems.
Because they keep communications equipment closer to Earth than satellites, the stations could offer stronger, higher-capacity signals. This would enable real-time communications speedy enough to communicate with standard smartphones, high-resolution capabilities for imaging tasks and greater sensitivity for sensing applications. They transmit data via free-space optics, or light beams, and large-scale antenna array systems, which can send large amounts of data quickly.
Satellites can be vulnerable to eavesdropping or jamming when their orbits bring them over adversarial countries. But platform stations remain within the airspace of a single country, which reduces that risk.
High-altitude platform stations are also easier to put in place than satellites, which have high launch and maintenance costs. And the regulatory requirements and compliance procedures required to secure spots in the stratosphere are likely to be simpler than the complex international laws governing satellite orbits. Platform stations are also easier to upgrade, so improvements could be deployed more quickly.
Platform stations are also potentially less polluting than satellite mega-constellations because satellites burn up upon reentry and can release harmful metals into the atmosphere, while platform stations can be powered by clean energy sources such as solar and green hydrogen.
The key challenges to practical platform stations are increasing the amount of time they can stay aloft to months at a time, boosting green onboard power and improving reliability – especially during automated takeoff and landing through the lower turbulent layers of the atmosphere.
Beyond satellites
Platform stations could play a critical role in emergency and humanitarian situations by supporting relief efforts when ground-based networks are damaged or inoperative.
The stations could also connect Internet of Things (IoT) devices and sensors in remote settings to better monitor the environment and manage resources.
In agriculture, the stations could use imaging and sensing technologies to help farmers monitor crop health, soil conditions and water resources.
Their capability for high-resolution imaging could also support navigation and mapping activities crucial for cartography, urban planning and disaster response.
The stations could also do double duty by carrying instruments for atmospheric monitoring, climate studies and remote sensing of Earth’s surface features, vegetation and oceans.
From balloons to airplanes
Platform stations could be based on different types of aircraft.
Balloons offer stable, long-duration operation at high altitudes and can be tethered or free-floating. Airships, also known as dirigibles or blimps, use lighter-than-air gases and are larger and more maneuverable than balloons. They’re especially well suited for surveillance, communications and research.
Gliders and powered aircraft can be controlled more precisely than balloons, which are sensitive to variations in wind speed. In addition, powered aircraft, which include drones and fixed-wing airplanes, can provide electricity to communication equipment, sensors and cameras.
Next-generation power
Platform stations could make use of diverse power sources, including increasingly lightweight and efficient solar cells, high-energy-density batteries, green hydrogen internal combustion engines, green hydrogen fuel cells, which are now at the testing stage, and eventually, laser beam powering from ground- or space-based solar stations.
The evolution of lightweight aircraft designs coupled with advancements in high-efficiency motors and propellers enable planes to fly longer and carry heavier payloads. These cutting-edge lightweight planes could lead to platform stations capable of maneuvering in the stratosphere for extended periods.
Meanwhile, improvements in stratospheric weather models and atmospheric models make it easier to predict and simulate the conditions under which the platform stations would operate.
Bridging the global digital divide
Commerical deployment of platform stations, at least for post-disaster or emergency situations, could be in place by the end of the decade. For instance, a consortium in Japan, a country with remote mountainous and island communities, has earmarked US$100 million for solar-powered, high-altitude platform stations.
Platform stations could bridge the digital divide by increasing access to critical services such as education and health care, providing new economic opportunities and improving emergency response and environmental monitoring. As advances in technology continue to drive their evolution, platform stations are set to play a crucial role in a more inclusive and resilient digital future.
Mohamed-Slim Alouini, Distinguished Professor of Electrical and Computer Engineering, King Abdullah University of Science and Technology and Mariette DiChristina, Dean and Professor of the Practice in Journalism, College of Communication, Boston University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
STM Daily News is a vibrant news blog dedicated to sharing the brighter side of human experiences. Emphasizing positive, uplifting stories, the site focuses on delivering inspiring, informative, and well-researched content. With a commitment to accurate, fair, and responsible journalism, STM Daily News aims to foster a community of readers passionate about positive change and engaged in meaningful conversations. Join the movement and explore stories that celebrate the positive impacts shaping our world.
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