Happy Thursday. I’m Corinne Purtill, a science and health reporter for The Times, filling in this week for the incomparable Sammy Roth.

Last week my family drove north from Los Angeles on State Route 99 toward Yosemite, exactly 157 years and five days after a 29-year-old John Muir set out on foot for the same destination from San Francisco.

There have, admittedly, been some changes in what is now Yosemite National Park since the Scottish-born naturalist began his hike equipped with little more than a pocket map and the confident assurance, he later wrote, “that Yosemite Valley lay to the east and that I should surely find it.”

Muir encountered a valley floor uncluttered by paved roads, or cars, or clusters of tourists gaping at the rock climbers dangling from El Capitan’s sheer face. But on the timescale of the geologic and glacial processes that shaped Yosemite, our visits occurred hardly a breath apart. Muir’s description of the marvel he found upon could have easily been written last week.

“The Valley, comprehensively seen, looks like an immense hall or temple lighted from above,” Muir wrote of his first impressions. “But no temple made with hands can compare with Yosemite. Every rock in its walls seems to glow with life . . . while the snow and waterfalls, the winds and avalanches and clouds shine and sing and wreathe about them.”

Yosemite’s timeless granite cathedrals and snow-melt-swollen waterfalls are awe-inspiring. Yet as we drove each day from our rented cabin in the nearby Stanislaus National Forest to the park’s western entrances, a very different sight rendered us speechless: acres upon acres of scorched landscape and charred, dead trees, the remains of once-lush forests devastated in the 2013 Rim fire.

The forests of the high Sierras have evolved to co-exist with fire. Blazes sparked by lightning or intentionally lit as part of indigenous land-management practices have been part of the ecosystem for millennia, clearing away invasive species and excess vegetation and encouraging new growth. Some native trees are “serotinous,” which means they rely on wildfire heat to trigger the dispersal of new seeds from their cones.

But the kind of massive, high-intensity, out-of-control wildfires sparked by a changing climate are something else entirely.

Ignited by a hunter’s illegal campfire on Aug. 17, 2013, the Rim fire consumed more than 257,000 acres (400 square miles) overall, including some 77,000 in the bounds of Yosemite.

One-third of that acreage burned hot enough to entirely destroy 75% to 100% of the standing trees, leaving essentially nothing of the original forest alive to regenerate, said John Buckley, a former hotshot firefighter for the U.S. Forest Service who is executive director of the Central Sierra Environmental Resource Center, a nonprofit that works on wildlife, water and ecology in the northern Yosemite region.

While controlled burns and wildfire management efforts carried out in previous years helped keep the Rim fire’s spread in check to some degree, the its and intensity still led to massive tree mortality in some areas, creating conditions ripe for the next megafire.

“Those are the places that really haunt us today,” said Scott Stephens, a UC Berkeley professor of fire science and forest policy.

More than a decade later, there are still up to 300 snags — dead standing trees — per acre in some of Yosemite’s most intensely affected areas, Stephens said. That translates to about 150 tons per acre of dead biomass in addition to any new growth that have sprung up, all of it a spark away from the next conflagration. “So,” he said, “the next fire in that system will be an intense one.”

There will undoubtedly be a next one. At the time it occurred, the Rim fire was the third-biggest in California’s recorded history. Some 12 fiery years later, it doesn’t even crack the top 10.

A national park is a miracle of time, a place to marvel that our puny run as a species managed to intersect with the eons-long processes that shaped these breathtaking landscapes.

Right now, they are also places that lay bare how rapidly human-caused climate change can transform these ecosystems in ways that render them inaccessible for the duration of our lifetimes.

I last visited Yosemite as a child with my parents, but my children did not see the same park I did, and they never will. The Rim fire made sure of that. Within the blip of a single generation, swaths of millennia-old forest were transformed into charred landscape that physically cannot return to their former state within the course of my lifetime, or that of my children.

With careful stewardship, replanting and responsible fire management, it would be possible to nurture a young forest that “would be probably pretty darn beautiful” within the course of a few generations, Stephens said. But that takes investment and personnel, things that are highly imperiled in the National Park Service under the current Trump administration. Representatives of the park contacted for this story declined to speak.

“If we did that work in there proactively, when the next Rim fire comes, I think easily 50% of the [tallest] trees would survive. It’d be a victory,” Stephens said. “But in the current condition, it’s just as vulnerable as what we saw the Rim fire burn into.”

Here’s what’s happening elsewhere in the world of climate change and the environment.

Last week, as my colleagues Tony Briscoe and Hayley Smith reported, the Los Angeles County Department of Public Health released preliminary test results from hundreds of soil samples collected in areas affected by the Palisades and Eaton fires.

In somewhat encouraging news, samples from the Palisades area returned little evidence of contamination beyond some isolated spikes of heavy metals and polyaromatic hydrocarbons.

The same could not be said for neighborhoods affected by the Eaton fire.

More than one-third of samples collected within the Eaton burn scar exceeded California’s health standard of 80 milligrams of lead per kilogram of soil. Nearly half of samples just outside the burn scar’s boundary had lead levels above the state limit.

And downwind of the fire’s boundary, between 70% and 80% of samples surpassed that limit.

The county is for now shouldering the responsibility of contaminant testing because, as Tony first reported in The Times, the federal government has departed from a nearly two-decade tradition of testing soil on destroyed properties cleaned by the U.S. Army Corps of Engineers after fires.

Previously, the Army Corps would scrape 6 inches of topsoil from cleared properties and then test the remaining earth. If those tests revealed lingering contamination, it would scrape further.

After 2018’s Camp fire in Paradise, testing on 12,500 properties revealed that nearly one-third still contained dangerous levels of contaminants even after those first 6 inches of topsoil were removed.

The county has so far shared only results from standing homes, which are not eligible for the Army Corps of Engineers cleanup. Results from parcels with damaged or destroyed structures are still pending.

Frustrated with the slow trickle of data coming from the government, some Altadena residents are taking testing into their own hands. This week my colleague Noah Haggerty reported on the efforts of a grassroots organization called Eaton Fire Residents United, which found lead in every single one of the 90 homes for which they’ve collected test results. Of those, 76% were above EPA limits.

On Tuesday, the county Board of Supervisors voted unanimously to divert $3 million from the county’s 2018 $134-million settlement with lead-paint manufacturers to test residential properties that are both downwind and within one mile of the Eaton burn scar boundary. This is an issue The Times is following closely, and we’ll have a great deal more to tell you soon. All I can say for now is: Watch this space.

“Nobody wants to be in the center of chaos.”

That’s what almond farmer Christine Gemperle told Times reporter Ian James on his visit to Ceres, Calif., a farming community near Modesto. She was speaking about the fear and uncertainty that Trump’s tariff vacillations have created for farmers across California, the nation’s top agricultural exporter.

In 2022 alone, the state shipped nearly $24 billion of nuts, rice, tomatoes and other tasty goodness around the world.

But as China, Canada and other countries retaliate against U.S. tariffs by imposing their own taxes on American goods, California’s farming businesses could bear the costs, Ian reports.’

Canada, one of several unexpected bogeymen in the second Trump administration, is the top foreign buyer of California’s wine, strawberries, lettuce and oranges, among other agricultural exports, followed by the European Union and China.

But this productive trade relationship is beginning to fall apart. In addition to Canada’s 25% tariffs on many U.S. goods, Canadians have also begun to boycott American products.

Gemperle‘s 135 acre farm is among the California growers who together produce more than three-quarters of the world’s almonds. Things weren’t easy under the first Trump administration, she told Ian. The adoption of U.S. tariffs in 2018 prompted China to retaliate. Gemperle watched business slip away to places like Australia instead, she said.

It’s too soon to know how this trade chaos will play out, but the uncertainty is already keeping her up at night.

“Farming is uncertain and a risk and a gamble, as it is. We don’t need more of that,” she said. “It’s all just overwhelming.”

The news from the sea has not been great lately.

The remains of a dead gray whale washed ashore last week in Huntington Beach. At least 70 more have died this year in Baja California’s lagoons.

Scores of sea lions and dolphins have been fatally poisoned in recent months by domoic acid, a neurotoxin produced by harmful algal blooms. Animal rescue shelters are filling up with sick and starving brown pelicans and their malnourished orphaned chicks — further victims of the domoic acid outbreak.

So props to Times wildlife reporter Lila Seidman for finding a piece of positive marine news. And yes, since you were wondering — it does involve sunflower sea star sperm!

Sunflower sea stars thrived along the Pacific Coast until 2013, when a mysterious disease linked to a marine heat wave destroyed about 99% of California’s population. With their former predators out of the picture, purple sea urchins proliferated. Kelp, the urchins’ favorite food, collapsed. Lila reports on the efforts to revitalize the population through lab-raised sea stars. Read her fascinating story, which begins with an unexpected but well-timed release of sea star sperm just before a planned spawn.

“The nice thing is they had six males go off, and so [with] all that sperm . . . we can hit the ground running,” Lila’s source told her. Finally, a sea story with a happy ending.

This is the latest edition of Boiling Point, a newsletter about climate change and the environment in the American West. Sign up here to get it in your inbox. And listen to our “Boiling Point” podcast here.