Global warming caused by human activities — mostly the burning of oil, gas and coal — is raising average temperatures in the United States more quickly than it is across the rest of the planet. The report issued Tuesday, the National Climate Assessment, is the government’s premier compilation of scientific knowledge on what this means for the country and how Americans are responding.

“Too many people still think of climate change as an issue that’s distant from us in space or time or relevance,” said Katharine Hayhoe, an atmospheric scientist at Texas Tech University who contributed to the report. The new assessment, the fifth of its kind, shows “how climate change is affecting us here, in the places where we live, both now and in the future,” she said.

Human-driven warming is intensifying wildfires in the West, droughts in the Great Plains and heat waves coast to coast. It is causing hurricanes to strengthen more quickly in the Atlantic and loading storms of all kinds with more rain. So far this year, the nation has experienced a record 25 billion-dollar weather disasters, many of them exacerbated by the hotter climate.

“We’re sharing this report in detail with the American people so they know exactly what you’re facing,” said Mr. Biden, who sought to draw a distinction with his predecessor and likely challenger in the 2024 presidential election, Donald J. Trump.

In 2018, the Trump administration published the fourth National Climate Assessment on the day after Thanksgiving, with several officials acknowledging at the time that they hoped it would not receive much attention. Mr. Trump later disbanded a federal advisory committee that was charged with translating the report into guidance for local governments and private companies.

By contrast, Mr. Biden said Tuesday that along with the report, his administration created an online tool to enable people to see the impacts of climate change in their city and state.

Mr. Biden also announced the allocation of about $6 billion to strengthen the electric grid, help deploy carbon-free energy and protect communities from the impacts of climate change and improve water reliability in Western states. “We need to do more and move faster,” he added.

The report issued Tuesday points out that cost-effective tools and technologies to significantly reduce America’s contribution to global warming already exist. U.S. emissions of heat-trapping gases fell by 12 percent between 2005 and 2019 as the country has shifted from coal toward natural gas and renewable sources. And options are increasing for electrifying energy use, reducing energy demand and protecting natural carbon sinks like forests and wetlands, the report says.

Even so, the United States and other industrialized countries are still curbing their emissions so sluggishly that a certain amount of additional greenhouse warming is essentially locked in, forcing societies to learn to live with the effects. On this front, the report concludes that Americans’ efforts have mostly been “incremental” instead of “transformative”: installing air-conditioners rather than redesigning buildings, increasing irrigation rather than reimagining how and where crops are grown, elevating homes rather than directing new development away from floodplains.

Americans, the report says, need to make deeper changes to the ways they work, manage their environments and move through them to become resilient to the climate conditions that humanity’s past choices have brought about, conditions that Earth has never before experienced while hosting so many members of our species.

Federal agencies have produced new assessments twice a decade or so since 2000, as mandated by a 1990 law.

The new report comes as President Biden seeks re-election. While Mr. Biden signed the nation’s first climate law and has proposed regulations to significantly cut emissions from tailpipes and smokestacks, many young voters who are alarmed by global warming are angry about his decision to greenlight new oil drillingin Alaska. Biden administration officials said the assessment’s findings showed how the president’s policies were moving the nation toward a clean-energy future.

“We’ve got climate solutions that can be made in America and are being made in America, that we’re deploying brick by brick and block by block,” said Ali Zaidi, the White House national climate adviser. “That gives us hope.”

Every part of the country is feeling the effects of the warming planet, the report finds. Rising fatalities from extreme heat in the Southwest. Earlier and longer pollen seasons in Texas. Northward expansion of crop pests in the Corn Belt. More damaging hailstorms in Wyoming and Nebraska. Stronger hurricanes in Puerto Rico and the Virgin Islands. Shifting ranges for disease-spreading ticks and mosquitoes in many regions.

The latest climate assessment is the first to include a dedicated chapter on economics, reflecting scholars’ growing interest in pinning down both the direct costs of climate change and its wider effects on households, businesses and markets, said Solomon M. Hsiang, a professor of public policy at the University of California, Berkeley, who helped lead the writing of the chapter.

These effects vary between regions, with hotter ones facing more harm and colder ones potentially benefiting. But the report cites studies showing an overall loss in the nation’s economic well-being. For every 1 degree Fahrenheit that the planet warms, the U.S. economy’s growth each year is 0.13 percentage points slower than it would be otherwise, the report finds, a seemingly small effect that can add up, over decades, to a sizable amount of forgone prosperity.

Such metrics do not, however, capture the full effects of warming on less-tangible things Americans value, including human health, ecosystems, trades like fishing that are passed down over generations and even recreational activities such as skiing, camping and other outdoor pastimes that wildfire smoke and scorching heat increasingly lace with peril. “Nonmarket effects of climate change in many cases are some of the largest,” Dr. Hsiang said.

The assessment finds that efforts to plan for climate threats have expanded in recent years. Around two in five states and 90 percent of U.S.-based companies have assessed their climate risks. Eighteen states have climate adaptation plans; another six are working on theirs.

So far, though, implementation has been “insufficient,” the report concludes. Funding is a challenge, it says, but so is coordination.

The assessment cites a few programs in California and Florida that have tried to plan for climate adaptation across city and county lines. Yet when not properly designed and monitored, adaptation efforts can lead to unintended side effects, said Katharine J. Mach, an environmental scientist at the University of Miami who contributed to the report. “In some cases, we may be working well on climate but creating other issues,” she said.

Disaster relief, for example, goes disproportionately to cities and towns, which could be exacerbating urban-rural disparities, Dr. Mach said. Federal buyouts of homes in vulnerable places have occurred disproportionately in wealthy counties, largely because agencies there can better navigate the bureaucratic requirements.

The assessment acknowledges America’s progress toward pumping less carbon into the atmosphere but says the country must do more — and much, much faster. Emissions from generating electricity in the United States are down about 40 percent from 2005. Yet emissions from transportation rose by nearly 25 percent between 1990 and 2018, even as vehicles became more energy efficient. The reason? Americans are driving more.

“People sometimes focus so much on the stuff that we don’t know how to do that it paralyzes them in thinking about the options that we have today,” said Steven J. Davis, a professor of earth systems science at the University of California, Irvine, and another author of the report.

Still, solar and wind facilities will require enormous amounts of land, potentially 3 to 13 percent of the area of the contiguous United States, the report finds. Around 8 million Americans, or 5 percent of the labor force, work in energy-related jobs, many of which are at risk in the shift to renewable sources. The Biden administration’s plans for offshore wind power have run into trouble as rising interest rates, supply chain delays and local opposition stymie projects.

Dr. Davis expressed optimism that the hurdles could be navigated. The assessment cites analyses showing that clean energy and related industries can create enough jobs to offset declines in fossil-fuel employment. Switching to zero-carbon energy could reduce air pollution enough to prevent 200,000 to 2 million deaths by 2050, the report says.

“It’s not all bad trade-offs,” Dr. Davis said.

Nov. 14, 2023

The discovery, made in caterpillars and described Monday in The Proceedings of the National Academies of Sciences, is “robust” evidence that “more than one virus has evolved to selectively kill male insects,” said Greg Hurst, a symbiont specialist at the University of Liverpool in England who wasn’t involved in the study. That could one day help control populations of pest insects and disease vectors like mosquitoes.

“I expect there are a lot more cases like this that will be discovered in the near future,” said Daisuke Kageyama, a researcher at the National Agriculture and Food Research Organization in Japan and one of the study’s authors.

The virus was found by chance. Misato Terao, a research technician at Minami Kyushu University, was straightening up the campus greenhouse when she found unwelcome intruders — fat green caterpillars — nibbling on the impatiens. She scooped them up and, on a whim, dropped them off in the lab of Yoshinori Shintani, an insect physiologist who is Minami Kyushu’s resident bug guy.

On a hunch, he bred the females from the greenhouse with male tobacco moths he found fluttering around the lights in his own home. The greenhouse moths only had daughters — and so did their daughters, and their daughters’ daughters. Over 13 generations of the moths’ descendants, only three had males.

Dr. Shintani and his colleague Dr. Kageyama quickly realized they had a “male-killer” on their hands.

For decades, scientists have known that microbial hitchhikers, usually bacteria, can take up residence in the jellylike cytoplasm of insects’ cells. And through a process that’s not very well understood, those microbes can be passed from mother to offspring.

Sometimes these microbial symbionts tamper with the host’s reproduction. From the symbiont’s perspective, “males are useless” because they can’t help propagate the microbe, Dr. Kageyama said. So the symbiont simply eliminates them. The bacteria Wolbachia can prevent male butterflies from being born. Other bacteria kill developing males before they hatch, reducing competition for the females and giving them a fortifying snack: the eggs that held their brothers.

Dr. Shintani’s team found that antibiotics didn’t knock out the male-killing effect in the greenhouse moth’s progeny, so bacteria couldn’t be responsible. Genetic analysis turned up telltale signs of a virus, but unlike any male-killer ever seen before. Only two male-killing viruses have ever been documented; the virus found by the Japanese researchers, which they named SlMKV, seems to have evolved separately.

To confirm the male-killer was actually infectious and inheritable, Dr. Shintani needed to juice some tobacco moths. He and his team blended the bodies of pupae and adult moths with SlMKV and injected the resulting slurry into the bodies of uninfected pupae and moths. That did the trick — the next generation heavily favored females, and in subsequent generations males vanished altogether.

Further experiments revealed just how lucky the researchers were to find this male-killer. While cool weather can be lethal to tobacco cutworms, SlMKV is vulnerable to heat, and the researchers found that the virus’s effect was diminished and eventually neutralized at higher temperatures. The tobacco cutworm’s native range is in subtropical parts of China and Taiwan.

The scientists suspect the balmy climate in the caterpillar’s home acts like a perpetual fever, suppressing the male-killing effect. It was pure chance that Japan’s mild temperatures fell in the “Goldilocks zone” in which SlMKV is active, and that scientists could therefore notice the sex imbalance in the greenhouse.

Outside experts say the team’s discovery is a sign that viral male-killers are more common than anticipated. And the find could have implications for controlling other important agricultural pests to which the tobacco cutworm is closely related, Dr. Hurst said.

Anything researchers can learn about male-killers helps advance the quest for the pest controller’s holy grail: a “female-killer,” which could help fight invasive pests or disease-carrying species such as mosquitoes.

According to Anne Duplouy, an evolutionary biologist at the University of Helsinki who studies microbial symbionts in insects, time is running out for humans to learn from these temperature-sensitive microbes. As the climate changes, she said, “we are likely to be losing many of these interactions” before they can be documented.

By Elizabeth Anne Brown

The institute reported that 3,500 square miles had been clear-cut between August 2022 and July 2023, a 22.3 percent decrease from the same period a year earlier. The decline in tree loss is estimated to have reduced the country’s greenhouse gas emissions by 7.5 percent. Brazil is the world’s sixth largest emitter, by some measures.

“Behind this was a political decision,” Marina Silva, Brazil’s environment minister, said on Thursday at a news conference. “We are changing the image of the country when we change this reality.”

The announcement was an encouraging sign that local policies could change the trajectory of global forest loss. The world lost 10.2 million acres of primary forest in 2022, a 10 percent increase from the year before, according to an annual survey by the World Resources Institute. Brazil accounted for more than 40 percent of the destruction recorded.

Two-thirds of the deforestation happened before Mr. Lula came into office, the government said. Under his predecessor, Jair Bolsonaro, deforestation rates climbed to a 15-year high as Mr. Bolsonaro’s administration loosened environmental protection policies.

Environmental fines in the Amazon more than doubled under Mr. Lula, the government reported, as his administration sought to rebuild the forest’s protection policies. Almost all of the deforestation in Brazil’s Amazon rainforest is illegal, mostly the result of land grabbing and farmers’ replacing trees with pasture.

Brazil isn’t the only country making progress in the region. Colombia, which has a tenth of the Amazon rainforest, announced on Tuesday that deforestation rates there had fallen by 70 percentin the first nine months of the year.

But El Niño, the climate pattern that has helped cause a historic drought fueling major wildfires in the region, may jeopardize some of the progress in the region, the environment ministers of both countries acknowledged.

More than a third of fires raging in the Brazilian Amazon are destroying old-growth forests, Ms. Silva said. “It’s a demonstration that the climate change is already impacting the forest,” she added.

The planet’s biggest freshwater tank is in trouble.

The Amazon rainforest, where a fifth of the world’s freshwaterflows, is reeling from a powerful drought that shows no sign of abating.

Likely made worse by global warming and deforestation, the drought has fueled large wildfires that have made the air hazardous for millions of people, including Indigenous communities, while also drying out major rivers at a record pace.

One major river reached its lowest level ever documented on Monday, while others are nearing records, suffocating endangered pink dolphins, shutting down a major hydropower plant and isolating tens of thousands living in remote communities who can only travel by boat.

“There’s just dirt now where the river used to be,” said Ruth Martins, 50, a leader of Boca do Mamirauá, a tiny riverside community in the Amazon. “We’ve never lived through a drought like this.”

“This is a catastrophe of lasting consequences,” said Luciana Vanni Gatti, a scientist at Brazil’s National Institute of Space Research who has been documenting changes in the Amazon. “The more forest loss we have, the less resilience it has.”

Recent studies have shown that climate change, deforestation and fires have made it harder for the Amazon to recover from severe droughts.

And, Ms. Gatti warned, the worst may be yet to come. The rainy season is expected to start in the next weeks and if the drought, which started in June, persists it would mark the first time such extreme conditions took hold in the Amazon’s driest period and continued into its wettest.

In Tefé, a rural municipality in the northwestern Amazon, residents are crossing muddy stretches of lake bed on motorcycles and paddling canoes down narrow streams that were once rivers. Some 158 riverside villages in the same region have been left stranded as waterways linking them to bigger towns have dried up, said Edivilson Braga, coordinator of the local civil defense service.

The Amazon has experienced droughts in the past, but it’s now facing “simultaneous disasters,” said Ayan Santos Fleischmann, a hydrologist at the Mamirauá Institute, a research organization based in Tefé. Scarce rainfall, scorching heat and scalding water temperatures are battering the region all at once.

“This is a crisis — a humanitarian, environmental and health crisis,” said Dr. Fleischmann. “And what scares us most is what lies ahead.”

In Boca do Mamirauá, about two hours by speedboat from Tefé, drying waterways have caused stocks of basic food items and medications to dwindle and prevented children from making the river journey to school since Sept. 20, said Ms. Martins, the community leader.

Across the Amazon, wells and streams have dried up, leaving communities without clean drinking water. “The water turned to mud here,” said Tuniel Gomes Figueiredo, who lives in Murutinga, an Indigenous village of about 3,000 people.

With no alternative, some residents are drinking, cooking and bathing with contaminated water. “This water is making children sick, it’s making elderly people sick,” Mr. Braga said. Health authorities also worry that stagnant pools of overheated water could breed mosquitoes carrying malaria and dengue.

The drought has stressed countless animal species in a region known for abundant wildlife. In Lake Tefé, water temperatures remain high and the carcasses of more pink river dolphins have surfaced over the last week, bringing the death toll to 153 since the first carcasses were recovered on Sept. 23, Dr. Fleischmann said.

While low humidity and high heat alone can kill some plants and animals, much of the destruction is caused by the drier forest’s increased vulnerability to fires typically started by farmers and others who clear the land. Wildfires have consumed more than 18,000 square miles of the Amazon since the start of the year, an area twice the size of Vermont.

Smoke from wildfires turned the air so hazardous in Manaus, a city of two million in the heart of the Amazon, that it recently became one of the most polluted cities on the planet, according to the World Air Quality Index project. Checking air quality data each morning has become an anxious habit in the city, as children and older people have ended up in hospitals struggling to breathe, according to doctors in Manaus.

Camila Justa, a veterinarian in Manaus, said she has never seen such heavy smoke blanket the sky and suffered an asthma attack for the first time in 20 years, while her 4-year-old son has had pneumonia twice since September.

“It’s really hard to fill your lungs with air,” she said. “And, when you do, it burns.”

The lack of rain in the Amazon is largely the result of two climate patterns, experts said.

From the west, El Niño, which warms waters in the Pacific near the Equator, is gaining strength. From the southwest, high temperatures in North Atlantic waters have accelerated the air flow toward the Amazon, preventing rain clouds from forming above the forest.

While the link between human-caused global warming and the drought is still unclear, climate models suggest that “over the next decades, with the increase in temperatures caused by climate change, these events will become more frequent,” said Gilvan Sampaio, a scientist monitoring climate patterns at Brazil’s National Institute of Space Research.

The effects of a changing climate are intensified by high deforestation levels in the Amazon, as farmers clear land for soy and cattle farms whose products are exported to countries around the world. Cutting down trees, like global warming, makes rain scarcer and temperatures higher because the Amazon’s trees release moisture, cooling temperatures and forming rain clouds.

Drying rivers are also a blow to the region’s economy. Barges that move corn bound for China and other countries were forced to reduce their cargo by half along an important river this month because the water was too shallow, and the erosion of a riverbed caused one port to collapse.

The Amazon’s rivers also fuel power plants that produce over a tenth of Brazil’s electricity and the lack of rain led one power plant to shut down.

Similar drought conditions were documented in 2015, contributing to the Amazon’s worst fire season on record. But scientists expect this drought to be even more devastating because the Atlantic Ocean is warmer and El Niño hasn’t yet reached its peak.

“This is just the beginning,” Dr. Gatti, the scientist, said.

On a recent afternoon, heavy clouds darkened the skies over the riverside village of Boca do Mamirauá. People scrambled to grab buckets, ready to fill them with rainwater. But the ominous clouds passed quickly. “Not a single drop,” Ms. Martins, the community leader, said.

“We’re just praying for the rain to come.”

By Ana Ionova and Manuela Andreoni

The wildfire was blazing a clear path toward a Canadian lakeside tourist spot in British Columbia with a population of 222,000 people.

The fire advanced on the city of Kelowna for 19 days — consuming 976 hectares, or about 2,400 acres — of forest. But at the suburban fringes, it encountered a fire prevention zone and sputtered, burning just a single house.

The fire prevention zone — an area carefully cleared to remove fuel and minimize the spread of flames — was created by a logging company owned by a local Indigenous community. And as a new wildfire has stalked the suburb of West Kelowna this month, its history with the previous one — the Mount Law fire, in 2021 — offers a valuable lesson: A well-placed and well-constructed fire prevention zone can, under the right conditions, save homes and lives.

It’s a lesson not only for Kelowna but also for a growing number of places in Canada and elsewhere threatened by increased wildfire amid climate change.

“When you think about how wildfire seasons are playing out, if we invested more into the proactive, then we would need less of that reactive wildfire response,” said Kira Hoffman, a wildfire researcher at the University of British Columbia. “We’re not going to see probably the effects of a lot of this mitigation and treatment for 10 or 20 years. But that’s when we’re really going to need it.”

Wildfires are an essential component of the natural cycle of forests, but in recent years, more of them have grown so big that containment is nearly impossible. Fire prevention zones — created in the off season — can help slow approaching blazes so that people can escape, and can also enable firefighters to gain control over some areas.

The creation of these zones is being greeted with renewed interest in parts of Canada, including in the western provinces of British Columbia and Alberta. Interest has especially peaked in Indigenous communities, which have been most affected by the country’s wildfires.

Ten times as many acres have burned in Canada this year than all of last fire season, at times sending smoke as far south as Georgia and as far east as Europe. The current fire in West Kelowna has breached areas that lack fire prevention zones, consuming 110 buildings and upending the lives of about 30,000 evacuees in the area.

Image: Sap from a scorched tree shows it survived a wildfire in West Kelowna, British Columbia. Credit: Amber Bracken for The New York Times

By contrast, the 50-acre fire resistant zone starved the in 2021 fire, allowing firefighters to suppress it, keeping it away from houses.

The logging company, Ntityix Development, that created that fire prevention zone drew in part on traditional Indigenous forestry practices, including thinning the forest; cleaning up debris on the floor; and burning the debris and ground cover in a controlled way to prevent it from becoming fuel for wildfires — an act once banned by the provincial government.

“This was the first test of any of the work that we’ve done and it indicates to me that it works,” said Dave Gill, the general manager of forestry at Ntityix Development, which is owned by the Westbank First Nation, as he walked through the still largely intact forest a few weeks before this year’s fire began. “It certainly stopped it advancing.”

Image: Dave Gill, the general manager of Ntityix Development, in an area of forest largely spared with the help of mitigation efforts. Credit: Amber Bracken for The New York Times

Ntityix’s strategy helps slow fires by reducing the flammability of forests showered by airborne embers, the main way wildfires spread, said Dr. Hoffman, a former wildfire fighter.

In 2015, six years before the Mount Law fire threatened Kelowna, Mr. Gill began creating the fire prevention zone, called the Glenrosa project, named after a forested neighborhood in West Kelowna. A key objective was keeping any fires on the forest floor.

“If you have a fire and it’s on a surface, it’s fairly easy to contain or to fight,” Mr. Gill said. “But as soon as it gets up into the crowns, it’s game over.”

The project also conserved mature trees with thick fire resistant bark and only harvested less valuable but more combustible young trees — a reversal of customary forestry practice.

Image: An area of managed forest in Nelson, British Columbia. During a forest fire, the low-lying vegetation and the organic content of the soil burn away, typically leaving mature trees scorched but alive. Credit: Amber Bracken for The New York Times

Before coming to Ntityix, Mr. Gill, who is not Indigenous, had a decades long career in government, as well as with commercial forestry and consulting companies.

He said the First Nation's elders, who have instructed him to manage the forest on a 120-year timeline, and his Indigenous co-workers changed how he thinks about the forest. “We’re leaving the trees that have the most timber value behind,” Mr. Gill, said. “This is trying to just instill a different paradigm in the way that you look at the forest, not just putting dollar signs on trees.”

After thinning the forest, Ntityix crews finished the project in 2016 by pruning the lowest 10 or 12 feet of limbs on the remaining trees so that they won’t become a ladder for fire to climb. The accumulated debris from the forest floor was either chipped and trucked away or burned.

In the areas where it is logging, Ntityix does not clear cut, the standard industry practice, but does some selective logging and leaves stands of fire resistant deciduous trees intact.

Image: The section wasn’t mitigated for wildfire and so most of the trees were killed in the 2021 fire. Credit: Amber Bracken for The New York Times

While billions of dollars have been spent putting out Canadian wildfires — British Columbia alone spent nearly 1 billion Canadian dollars in 2021 — funding for measures to make forests less welcoming to flames has generally been modest. Nor has the value of such measures been fully embraced by everyone in Canada’s forestry establishment.

Although more mitigation efforts are needed, their general effectiveness is being undermined by the growing intensity and size of wildfires, said Mike Flannigan, a wildfire scientist at Thompson Rivers University in Kamloops, British Columbias.

“When things get extreme, the fire will do what the fire will do,” he said. “Unless you treat 40 percent of the landscape, it’s not going to work because the fire will just go around it or jump over.”

Dr. Hoffman, however, is less pessimistic, and says that not enough large-scale risk reduction has been attempted to judge its effectiveness.

“There are not a lot of economic incentives for doing” what Ntityix did, Dr. Hoffman said. “It’s not really sexy to go and take out six-inch pine from the forest.”

The measures taken by Ntityix and other companies, many of them owned by First Nations communities or their members, are labor intensive and costly. The company has committed 100,000 Canadian dollars a year to carrying out a variation of its work that turns logging roads into wildfire mitigation zones, a process that will likely take decades.

Craig Moore — a member of the Syilx Okanagan Nation, in British Columbia — is also a former municipal firefighter and owns a company that does fire mitigation in forests.

Image: Craig Moore showing an area in British Columbia where fuel management — spacing trees and removing brush and lower branches of trees — has been effective in helping control wildfires. Credit: Amber Bracken for The New York Times

During an interview at his company, Rider Ventures, in Vernon, British Columbia, he recalled how his efforts slowed a fire in the province in 2021. Mr. Moore said that afterward, the area’s wildfire ranking fell from 6 — the most severe on the province’s scale — to 2, giving firefighters the chance to save 500 homes.

“Having water and trees are our biggest things,” Mr. Moore said, standing amid a forest where his company had worked. “If we lose that, we’re all going to perish pretty fast.”

Its aspens are growing at twice the speed normally expected, with fragrant sumac and tulip trees racing to catch up. It has absorbed storm water without washing out, suppressed many weeds and stayed lush throughout last year’s drought. The little forest managed all this because of its enriched soil and density, and despite its diminutive size: 1,400 native shrubs and saplings, thriving in an area roughly the size of a basketball court.

It is part of a sweeping movement that is transforming dusty highway shoulders, parking lots, schoolyards and junkyards worldwide. Tiny forests have been planted across Europe, in Africa, throughout Asia and in South America, Russia and the Middle East. India has hundreds, and Japan, where it all began, has thousands.

Now tiny forests are slowly but steadily appearing in the United States. In recent years, they’ve been planted alongside a corrections facility on the Yakama reservation in Washington, in Los Angeles’s Griffith Park and in Cambridge, where the forest is one of the first of its kind in the Northeast.

“It’s just phenomenal,” said Andrew Putnam, superintendent of urban forestry and landscapes for the city of Cambridge, on a recent visit to the forest, which was planted in the fall of 2021 in Danehy Park, a green space built atop the former city landfill. As dragonflies and white butterflies floated about, Mr. Putnam noted that within a few years, many of the now 14-foot saplings would be as tall as telephone poles and the forest would be self-sufficient.

Healthy woodlands absorb carbon dioxide, clean the air and provide for wildlife. But these tiny forests promise even more.

They can grow as quickly as ten times the speed of conventional tree plantations, enabling them to support more birds, animals and insects, and to sequester more carbon, while requiring no weeding or watering after the first three years, their creators said.

Perhaps more important for urban areas, tiny forests can help lower temperatures in places where pavement, buildings and concrete surfaces absorb and retain heat from the sun.

The Griffith Park forest occupies 1,000 square feet, and has drawn all manner of insects, lizards, birds and ground squirrels, along with western toads that journeyed from the Los Angeles River, Ms. Pakradouni said. To get to the forest, the toads had to clamber up a concrete embankment, traverse a bike trail, venture down another dirt embankment and cross a horse trail.

“It has all the food they need to survive and reproduce, and the shelter they need as a refuge,” Ms. Pakradouni said. “We need habitat refuges, and even a tiny one can, in a year, be life or death for an entire species.”

Dr. Miyawaki, who died in 2021 at the age of 93, developed his technique in the 1970s, after observing that thickets of indigenous trees around Japan’s temples and shrines were healthier and more resilient than those in single-crop plantations or forests grown in the aftermath of logging. He wanted to protect old-growth forests and encourage the planting of native species, arguing that they provided vital resilience amid climate change, while also reconnecting people with nature.

“The forest is the root of all life; it is the womb that revives our biological instincts, that deepens our intelligence and increases our sensitivity as human beings,” he wrote.

Dr. Miyawaki’s prescription involves intense soil restoration and planting many native flora close together. Multiple layers are sown — from shrub to canopy — in a dense arrangement of about three to five plantings per square meter. The plants compete for resources as they race toward the sun, while underground bacteria and fungal communities thrive. Where a natural forest could take at least a century to mature, Miyawaki forests take just a few decades, proponents say.

Crucially, the method requires that local residents do the planting, in order to forge connections with young woodlands. In Cambridge, where a second tiny forest, less than half the size of the first one, was planted in late 2022, Mr. Putnam said residents had embraced the small forest with fervor. A third forest is in the works, he said, and all three were planned and organized in conjunction with the non-profit Biodiversity for a Livable Climate.

“This has by far and away gotten the most positive feedback from the public and residents than we’ve had for any project, and we do a lot,” Mr. Putnam said.

Still, there are skeptics. Because a Miyawaki forest requires intense site and soil preparation, and exact sourcing of many native plants, it can be expensive. The Danehy Park forest cost $18,000 for the plants and soil amendments, Mr. Putnam said, while the pocket forest company, SUGi, covered the forest creators’ consulting fees of roughly $9,500. By way of comparison, a Cambridge street tree costs $1,800.

“A massive impact for a pretty small dollar amount in the grand scheme of the urban forestry program,” Mr. Putnam said.

Doug Tallamy, an American entomologist and author of “Nature’s Best Hope,” said that while he applauded efforts to restore degraded habitat, particularly in urban areas, many of the plants would eventually get crowded out and die. Better to plant fewer and save more, he said.

“I don’t want to throw a wet blanket on it, the concept is great, and we have to put the plants back in the ground,” Dr. Tallamy said. “But the ecological concept of a tiny forest packed with dozens of species doesn’t make any sense.”

Kazue Fujiwara, a longtime Miyawaki collaborator at Yokohama National University, said survival rates are between 85 and 90 percent in the first three years, and then, as the canopy grows, drop to 45 percent after 20 years, with dead trees falling and feeding the soil. The initial density is crucial to stimulating rapid growth, said Hannah Lewis, the author of “Mini-Forest Revolution.” It quickly creates a canopy that shades out weeds, and shelters the microclimate underneath from wind and direct sun, she said.

Throughout his life, Dr. Miyawaki planted forests at industrial sites globally, including at an automotive parts plant in southern Indiana. A turning point came when an engineer named Shubhendu Sharma took part in a Miyawaki planting in India. Enthralled, Mr. Sharma turned his own backyard into a mini-forest, started a planting company called Afforestt, and, in 2014, delivered a TED Talk that, along with a 2016 follow up, ended up drawing millions of views.

In the Netherlands, Daan Bleichrodt, an environmental educator, plants tiny forests to bring nature closer to urban dwellers, especially city children. In 2015, he spearheaded the country’s first Miyawaki forest, in a community north of Amsterdam, and has overseen the planting of nearly 200 forests since.

Four years later, Elise van Middelem started SUGi, which has planted more than 160 pocket forests worldwide. The company’s first forest was planted on a dumping ground alongside the Beirut River in Lebanon; others were sown later near a power plant in the country’s most polluted city, and in several playgrounds badly damaged by the 2020 blast at Beirut’s port.

And Earthwatch Europe, an environmental nonprofit, has planted more than 200 forests, most of them the size of a tennis court, throughout the United Kingdom and mainland Europe in the last three years.

Though many of the forests are still very young, their creators say there have already been outsize benefits.

The woodlands in Lebanon have drawn lizards, geckos, birds and tons of insects and fungi, according to Adib Dada, an architect and environmentalist and the main forest creator there. In the West African country of Cameroon, where eight Miyawaki forests have been planted since 2019, there are improved groundwater conditions and higher water tables around the forest sites, according to Limbi Blessing Tata, who has led the reforestation there. Crabs and frogs have also returned, she said, along with birds that were thought to be extinct.

According to Mr. Bleichrodt, a 2021 university study of 11 Dutch mini-forests found over 1,100 types of plants and animals at the sites — kingfishers, foxes, hedgehogs, spider beetles, ants, earthworms and wood lice.

“A Miyawaki forest may be like a drop of rain falling into the ocean,” Dr. Fujiwara wrote in an email, “but if Miyawaki forests regenerated urban deserts and degraded areas around the world it will create a river.”

“Doing nothing,” she added, “is the most pointless thing.”