Life on Earth depends on a delicate balance between ecosystems like rainforests, glaciers, oceans, and volcanoes, along with interconnected climate cycles. Around a decade ago, Johan Rockström, director of the Potsdam Institute for Climate Impact Research (PIK), introduced the concept of “nine planetary boundaries”—tipping points beyond which Earth’s ecosystems may no longer sustain life. In the 2024 Planetary Health Check Report, Rockström revealed that six of these boundaries have already been breached, and a seventh is nearing collapse due to human activities, posing a severe threat to life on Earth.
Representative Image Source: A conceptual image of Earth with one half showing lush greenery and the other half showing dry, cracked soil, representing environmental contrast. (Getty Images)
These findings were published in Science Advances. According to the Global Commons Alliance, the nine planetary boundaries include “biosphere integrity, climate change, land-system change, freshwater use, nutrient cycles, ocean acidification, aerosol pollution, ozone depletion, and novel entities like plastic pollutants.” Of these, six have already been disrupted, and the seventh—ocean acidification—is nearing its critical threshold, according to the 2023 health-check report.
“Our updated diagnosis shows that vital organs of the Earth system are weakening, leading to a loss of resilience and rising risks of crossing tipping points. Six of the nine planetary boundaries are transgressed and put into context in the report by high-resolution spatial maps of local and regional trends for all nine boundaries. The message is clear, local actions impact the planet, and a planet under pressure can impact everyone, everywhere. Securing human well-being, economic development, and stable societies requires a holistic approach where the protection of the planet takes center stage,” Levke Caesar, PIK Scientist and study lead author, said in a statement.
Representative Image Source: Close-up of children holding a planet at the beach (Getty Images)
In addition to this, Johan, who referred to planet Earth as a “patient,” said, “The overall diagnostic is that the patient, Planet Earth, is in critical condition. Six of nine Planetary Boundaries are transgressed. Seven PB processes show a trend of increasing pressure so that we will soon see the majority of the Planetary Health Check parameters in the high-risk zone.”
For the first time Patient Earth goes through a full Health Check. The verdict is clear – the patient is in critical condition. The 1st Planetary health check gives us the quantitative diagnosis required to guide the transformations for a safe landing https://t.co/O7ZqP6Npj8— Johan Rockström (@jrockstrom) September 25, 2024
Furthermore, the study revealed that the planetary boundary of climate change is in a high-risk zone, and the boundaries in land system change and freshwater change have also been transgressed, although to a lesser extent. Stratosphere ozone depletion has remained stable, according to The Guardian, but surprisingly, the atmospheric aerosol loading boundary has improved. But when it comes to the ocean acidification boundary, it is already at the tipping point. Ocean acidification, as per The Guardian, is “the phenomenon of increasing acidity (decreasing pH) in ocean water due to the absorption of atmospheric carbon dioxide.” Accumulation of excess carbon dioxide can pose a threat to living species that thrive in oceanic underwater.
Hindou Oumarou Ibrahim, Chair of the Planetary Guardians, said that indigenous people lived in harmony with the planet’s critical life-supporting processes for centuries, and replenished the overall health of Earth. But now, he said, people are killing life with an overdose of chemicals, destruction of nature, skyrocketing temperatures, and rising pollution. While these planetary health checks are vital for the effective functioning of Earth, they may not provide the answer to the perturbations caused by humans that are pushing the boundaries.
Squinting through my binoculars, I scanned the dense branches of a black spruce, trying my best to catch a glimpse of the thin legs of a small black, white and yellow songbird. I was on the hunt for a yellow-rumped warbler – a bird affectionately called “butter-butt” by bird-watchers after the distinctive buttery yellow patch of feathers above its tail.
Stephanie Szarmach holds a yellow-rumped warbler that was banded as part of a study.Johanna Beam
Once I spotted a flash of red on one of the bird’s legs, I knew that this individual was special – in fact, it was one that I already knew well. That’s because I had placed identifying bands on it the previous year as part of my Ph.D. research, and it was carrying a very important piece of new technology.
I played the high pitched “warble” of its song through a speaker placed below a mist net of fine, nearly invisible mesh. Thinking another male had intruded on his territory, the bird quickly descended. My tactic worked – he got caught in the net. As I gently removed him, I breathed a sigh of relief as I saw the Tic Tac-size device sitting on his back.
A yellow-rumped warbler wears a multisensor geolocator backpack.Stephanie Szarmach
Over the past year, this warbler carried a multisensor geolocator backpack throughout his migratory journey, recording the long trek from his breeding grounds in Anchorage, Alaska, to a yet unknown winter refuge and back again. Working with my Ph.D. adviser, evolutionary biologist David Toews, I deployed dozens of these cutting-edge tags to illuminate the migratory journeys of these high-latitude breeding warblers at a scale not previously possible for small birds.
Now, after a year of waiting, I finally had the data in hand.
How can scientists track small birds?
Researchers began tracking the movements of migrating birds in the late 1960s using radio telemetry, a technique that requires tagged birds to be physically followed with receiver equipment, sometimes aided by a small aircraft.
Then, as GPS became more widely available in the early 2000s, satellite tags let researchers accurately track birds remotely. However, GPS transmitters are hefty – even just the battery that powers them is too heavy to be carried by the majority of small migratory songbirds, which often weigh less than a spoonful of sugar.
To address this problem, researchers developed ingenious little light-level geolocators. These miniature tags minimize weight by containing only a tiny battery, clock, computer chip and light sensor. They store data internally rather than transmitting it – hence my need to recapture tagged birds a year later. Researchers infer a bird’s locations from the timing of sunrise and sunset, which vary predictably across the globe and throughout the year.
Light-level geolocators have openednew windows into themigrations of small birds, but they also have limitations: Their estimated locations can err by hundreds of miles, and this uncertainty becomes impractically high around the equinoxes, when day length is the same worldwide.
Each harness loop of the multisensor geolocator goes around one of the bird’s legs and the tag sits on the bird’s lower back.Stephanie Szarmach
More recently, researchers developed a newer method of geolocation that uses atmospheric pressure to circumvent these limitations. When a bird ascends during a migratory flight, a barometric geolocator records a steep drop in air pressure, capturing the timing of departure and arrival for every stop along a bird’s migration route. In between flights, the pressure the tag records reflects the elevation at the bird’s position.
Knowing the bird’s elevation helps to narrow down possible locations, which researchers can then refine further by comparing the change in pressure over time recorded by the tag to global weather data using the computer program GeoPressureR. The unique pattern of rises and falls in pressure acts as a kind of pressure fingerprint for a specific location. Including light and wind data in the model of the bird’s movements can increase precision even more.
Atmospheric pressure data collected from a multisensor geolocator carried by a yellow-rumped warbler over five days in spring. When the bird is stationary, such as when resting at a stopover site, the measured pressure remains steady. During migratory flights, when the bird ascends into the sky, the pressure drops and fluctuates dramatically.Stephanie Szarmach
New tech answers an old question
We used these new multisensor backpacks to study the migration patterns of myrtle warblers, the northern subspecies of yellow-rumped warbler, which breed across North America’s boreal forest. Myrtle warblers in the northeast are known to winter along the Atlantic and Gulf coasts, but where northwestern populations migrate has been more of a mystery. In 1899, ornithologist Richard McGregor observed myrtle warblers wintering in coastal California, and hypothesized that these birds might breed in Alaska and British Columbia.
Using these new tags allowed us to test whether warblers breeding in Anchorage, Alaska, actually followed the shortest migration route to winter in California. To our surprise – and probably to McGregor’s as well, if he were still alive – we found that all the birds we tracked traveled east across the boreal forest of Canada before shifting south to the Gulf Coast – certainly not the Pacific Coast route we expected.
All told, this 6,800-mile (10,900-kilometer) round-trip journey was much longer than we anticipated for a species commonly considered a short- or medium-distance migrant.
Researchers tracked the routes six myrtle warblers flew on their fall migration southeast from Anchorage, Alaska.Figure by Stephanie Szarmach. Warbler illustration by Emily Griffith
Why take such a circuitous route?
The long, seemingly suboptimal route taken by our Alaskan myrtle warblers is actually mirrored by some other songbird species tracked from northwestern North America, including blackpoll warblers and Swainson’sthrushes.
Part of this pattern may relate back to the glaciations that isolated ancient populations of birds millions of years ago. The thinking goes that as these glaciers spread, they squashed the ranges of formerly northern species into the south. Then, as the glaciers slowly receded, the forests gradually reexpanded.
As more land opened up, birds moved farther north and west into that habitat. Each season some birds went a little farther as the forest available in their northern breeding grounds expanded. For migratory species such as myrtle warblers, the farther north and west their breeding range expanded, the longer the migration to their southern wintering ground became.
Scientists think migration routes are genetically encoded. The birds’ genes may have traced this expansion front, like Hansel and Gretel putting down breadcrumbs as they journeyed deeper and deeper into the forest. Today’s migration routes still trace that incrementally expanded path, even though the glaciers that shaped the original boundaries are long gone.
We’re still not sure exactly where the California-wintering myrtle warblers spotted in the 1800s are breeding. We suspect that a small proportion of the Anchorage-breeding birds may migrate to California, but that most of them travel from more distant, unstudied regions of Alaska or Yukon. Future research, potentially tagging myrtle warblers directly on the California wintering grounds, will shed more light on this population and why certain individuals follow a different migration route.
Barometric geolocation provides new data
Today, this new geolocation approach improves scientists’ ability to study the migrations of small birds and supports more effective conservation actions across the course of the entire year. More precise location estimates help researchers identify key stopover and wintering sites in need of protection and better understand the threats birds face throughout their journeys. These geolocators also reveal the altitude of migratory flights, which is important for understanding the risk of birds colliding with buildings or wind turbines.
Because these new tags capture pressure data for every migratory flight, they’re especially valuable for studying migration timing. Researchers have combined data from over 50 bird species to understand at what time of day or night different birds migrate. Now, as a postdoctoral researcher at the Smithsonian Migratory Bird Center, I am integrating multisensor geolocator data with satellite imagery to investigate how arrival and departure decisions throughout a bird’s migratory journey relate to seasonal changes in plant growth.
Scientists have now tracked dozens of bird species with multisensor geolocators, and that number increases every year. Each mapped migratory journey improves our understanding of how small birds migrate, what factors shape their movements and how best to protect them.
Fallen leaves shelter next spring’s pollinators and feed the soil. A horticulture specialist explains how to make room for both nature and a tidy yard.
Assistant Extension Professor of Horticulture and Ornamental Horticulture Specialist, University of Maine
Every autumn, homeowners and gardeners tend to engage in a familiar ritual. As trees shed their leaves, people drag out rakes, leaf blowers and lawn bags to strip their yards bare before winter arrives.
It is a tidy habit rooted in aesthetics, but ecologically, clearing away fallen leaves strips the very foundation of local ecosystems. Far from dead debris requiring disposal, this fallen foliage forms a dynamic layer and a biological interface that drives nutrient cycling and is essential for soil health and the environment, including biodiversity.
Here is the science behind why the first step of fall yard care could simply be doing less – along with practical ways to keep your yard looking neat while nourishing the ecosystem underneath.
A winter sanctuary for native pollinators
To understand why leaf litter matters, it helps to look closely at what happens beneath the surface as temperatures drop. While honeybees pass the winter in sheltered hives, the vast majority of North America’s native pollinators do not.
Raking, bagging and blowing leaves away destroys this crucial winter nursery.
Many other insects depend on the shelter of fallen foliage:
Moths and butterflies: Species such as the luna moth (Actias luna) and the Isabella tiger moth, whose caterpillar form is the woolly bear, spin cocoons or roll themselves directly inside fallen leaves. Raking or shredding those leaves destroys the next generation.
Fireflies: Adult fireflies lay eggs in moist soil, and their larvae spend up to two years hunting for their food, soft-bodied invertebrates under damp leaf litter. Raking deprives them of moisture and habitat.
In addition to being a shelter, fallen leaves are an evolved biological mechanism for nutrient cycling. Trees actively pump vital elements, including calcium, magnesium, potassium and nitrogen from deep subsoils, into their foliage. When autumn comes and leaves drop, these stored nutrients are deposited back into the soil.
Leaving leaves in place triggers fundamental ecological benefits.
A thick blanket of intact leaves acts as a natural insulator for the ground. Air pockets trapped between overlapping leaves moderate the soil temperature and slow heat transfer, buffering against the freeze-thaw cycles that heave soil, fracture plant roots and expose beneficial soil microbes to lethal cold. The intact leaf blanket also conserves moisture and prevents soil from drying out over the winter.
Adopting a softer approach to fall cleanup does not mean your yard has to look completely untamed or that you have to risk killing your lawn. Here is how to balance suburban expectations with sound ecological science:
Move, don’t remove: Move the leaves from lawns and sidewalks, rake them into garden beds, around ornamental plants or into vegetable plots, using manual rakes or electric leaf blowers. Aim for a layer 2 to 3 inches deep. Leaving leaves in grassy areas can help ticks hide there too, but if you move the leaves to garden beds or spots that are used less, the ticks will be less likely to nest in the grass. Establishing pollinator zones on the property can also help reduce tick populations.
Skip the leaf shredder: Mowing over leaves with a mulching mower is better than sending them to landfills, but high-velocity mower blades still kill overwintering insect eggs, chrysalises and larvae. Leave leaves intact wherever possible in plant beds.
Wait for spring to clean up: Do not cut back hollow-stemmed perennials or clear leaf beds during early, warm spring days. Wait until temperatures consistently stay above 50 degrees Fahrenheit (10 degrees Celsius) so overwintering bees and butterflies have time to safely emerge.
When you bag leaves for disposal and then buy commercial wood mulch or synthetic fertilizers in the spring, you are effectively paying a price for what your trees provided for free. By rethinking the cultural expectation of pristine autumn lawns, it’s possible to transform silent landscapes into vibrant habitat sanctuaries, simply by stepping back and allowing natural processes to take over.
The District of Columbia Water and Sewer Authority—now known as D.C. Water—has long provided water and sewer services to Washington, D.C. But for the past decade, the utility has also had an unexpected side hustle: turning human wastewater into fertilizer with flourishing results.
At most wastewater treatment plants, flushed water is cleaned, while the remaining solid matter is hauled away for disposal. Over time, transporting and disposing of that waste can cost millions of dollars while increasing carbon emissions from the trucks carrying it. A decade ago, however, D.C. Water decided to invest in transforming the solid waste into “humanure” rather than throwing it away.
At the end of the wastewater treatment process, the collected human waste solids are processed into biosolid fertilizer using technology developed by Norwegian company Cambi. The process doesn’t just produce high-quality fertilizer—it also generates biogas that can be put to good use.
“So you get up to 40% more biogas,” Cambi CEO Eirik Fadnes said. “That biogas can be used to generate electricity to be used elsewhere in the wastewater-treatment plant or put on the grid and sold.”
D.C. Water sells the biosolid fertilizer under the brand name Bloom, and it’s already proving to be a success. Bloom has been used throughout the Washington, D.C., area by customers including Catholic University, Mount Olivet Cemetery, and the Franciscan Monastery. It’s also used on numerous lawns, school grounds, community gardens, and golf courses.
The numbers underscore D.C. Water’s success. To date, nearly 400,000 tons of Bloom have been sold across Washington, D.C., Maryland, Pennsylvania, and Virginia, generating $13.6 million in revenue. D.C. Water originally estimated it would take 20 years for Bloom to pay off its investment. But thanks to strong demand from institutions, landscapers, and local garden centers, the utility is now on pace to recoup that investment in just 12 years.
Bloom is also helping D.C. Water meet its environmental goals. By turning waste into a useful product instead of hauling it away for disposal, the utility has reduced its carbon footprint by roughly 50,000 metric tons of CO₂ emissions each year—the equivalent of taking more than 11,700 gas-powered cars off the road annually. The process also produces biogas, which can be converted into electricity to help offset the energy costs of wastewater treatment.
Human waste works wonders
None of this would matter if human biosolids weren’t effective at improving soil. “Humanure,” a term coined by Joseph Jenkins, refers to compost made from properly treated human waste. Because human feces can contain disease-causing pathogens, it must be handled carefully. After all, we call it “waste” for a reason.
When human waste is composted correctly, naturally occurring microbes break down the organic material while generating enough heat to destroy harmful pathogens. Over time, the result is a nutrient-rich compost that can improve soil health. Some farmers even build specialized outdoor composting toilets to create humanure for use on their land.
Should D.C. Water continue on this path of simultaneous profitability and environmental improvement, it’s likely other wastewater treatment plants will follow its lead.
