In the winter of 1861, a series of deadly storms swept across California and the Pacific Northwest for nearly a month and a half, creating one of the wettest periods the region has experienced in the last two millennia. The Sacramento Valley became a 300-mile inland sea. The Los Angeles River burst its banks and swept away much of the recently incorporated city of Los Angeles.

Flooding stretched down the West Coast, from British Columbia to Baja California, killing up to 1,000 people, drowning 200,000 head of cattle — livestock that accounted for roughly a quarter of the state’s tax base — and causing property damage estimated in the tens of millions of 1860’s dollars. And yet, today, almost nobody is aware it happened.

This forgotten flood is exactly the kind of event USC Dornsife scholars and alumni — working across the nation, from Alaska to the Florida Keys — are bringing back into focus. As the nation marks its 250th anniversary, they are studying evidence preserved in ice cores, sediment layers, fire scars and long-term ocean records to understand how climate change is reshaping America’s lands, coasts and waterways — and to help communities prepare for what comes next.

The Flood That Time Forgot

“How did we forget this?” asks Will Cowan ’21, an environmental historian at Cal Poly Pomona who earned his PhD in history from USC Dornsife.

Cowan has spent years studying the evidence left by the 1861-62 flood, including tree rings, lakebed sediment cores and the accounts of those who endured its terror and destruction. He concluded that the flood was no freak event, but a product of natural processes that define the North American continent — processes that global warming is now intensifying.

“A warming Earth results in a warmer atmosphere, which carries more water,” he says. “That leads to deeper droughts and far more powerful, wetter storms.”

A System Out of Balance

The 1860s flood was driven by atmospheric rivers — vast currents of Pacific moisture that sweep inland each winter, delivering much of California and the Northwest’s precipitation. Most years, these storms replenish reservoirs, recharge soils and feed the grasses that blanket California’s hillsides. By summer, that lush growth has dried into tinder. It’s a cycle that has long governed the West — rain feeding growth, growth feeding fire. But as temperatures rise, each swing is growing more extreme, resulting in wetter winters, drier summers and bigger fires.

“You can’t have fire without fuel,” Cowan says. “Atmospheric rivers bring the vegetation — tons of invasive grasses that cover our hillsides. Then summer comes, it dries out. Now you’ve got all that fuel, and it feeds bigger fires.”

For millennia, Indigenous Californians understood and managed that balance. Carefully timed, prescribed burns reduced fuel and prevented catastrophic wildfires. Indeed, Indigenous Californians saw fire not as an enemy but as a tool — one that kept ecosystems resilient.

Modern development disrupted that relationship. Rivers were forced into channels, flood plains paved over and fire aggressively suppressed. In doing so, the relationship between land and atmosphere, fire and flood has been weakened. The result, argues Cowan, is a system more prone to extremes — both more flammable and more flood-prone — and thus more dangerous.

“We tend to think all floods are bad and all fires are bad,” Cowan says. “But some fire is necessary. Most of Southern California’s vegetation needs fire to reproduce. And floods are also necessary. We flush a ton of our water out to the ocean trying to prevent another 1862. But in doing so, we’re not allowing flood waters to sit on the landscape, and that’s what is needed to recharge the aquifers. By trying to control everything, we’ve made both fire and flood more dangerous.”

Understanding the imbalance is one thing. Trying to do something about it is another — and that’s where the Huntington-USC Institute on California and the West (ICW), based at USC Dornsife, comes in. Historians led by ICW founding director William Deverell have been working with Indigenous communities to recover and implement that knowledge by conducting prescribed burns in the southern Sierra Nevada.

“Indigenous societies paid very close attention to fire,” says Deverell, divisional dean for the social sciences and professor of history, spatial sciences and environmental studies. “That’s something we’ve lost — and it’s a mistake.”

But restoring the balance will not be simple, Cowan points out. It will require not only restoring knowledge, but also rehabilitating a landscape that has been transformed for more than a century. Still, the California story sets the template for what USC Dornsife researchers are doing across the country: recovering the signals, decoding what they mean, and translating that knowledge into action.

When the Ground Gives Way

Thousands of miles north, USC Dornsife scholars are reading a very different landscape for similarly urgent signs of change.

Along Alaska’s Yukon River — which runs for roughly 2,000 miles from British Columbia in Canada through Alaska to the Bering Sea — vast stretches of permafrost have remained frozen for tens of thousands of years. In places, the frozen ground extends more than 180 meters deep. Now it is thawing, releasing water — along with everything else it has held for millennia — into the river. The thawing ground is itself a record, revealing what the Arctic has been storing and what it is now releasing into communities downstream.

What’s buried in the ice is alarming. In 2024, Earth scientist Josh West co-authored a study showing that large stores of mercury are now leaking into Alaskan ecosystems in a dangerous release of the toxic element he refers to as a “mercury bomb.”

“We think there’s more mercury locked in permafrost than in all the oceans, atmosphere and soils around the world combined,” says West, professor of Earth sciences and environmental studies. “It’s been locked away for all this time, and now the question is: How much of this highly toxic element might become mobilized? Will it be transported to the oceans? And if so, what will the consequences be — locally and globally?”

The mercury originates far from Alaska. Emitted by coal burning and mining, it drifts northward through the atmosphere before becoming trapped in Arctic soils and ice. Now as that ice thaws, it is reentering the environment.

To track the process, West’s team samples sediments from riverbanks and sandbars along the Yukon, where erosion exposes ancient soils. Satellite data shows how the river shifts, carving into the landscape and releasing buried mercury as it goes. Together, these data sources provide a clearer picture of how mercury moves from air to soil to water, how quickly that cycle is accelerating, and what it means for the people who depend on the river.

Communities at Risk

The consequences are already being felt. The Yukon’s salmon populations are collapsing under the combined pressures of warming waters and overfishing. Local communities turning to alternative species such as pike and whitefish face greater mercury exposure.

“Getting the messaging right is tricky,” West says. Communities along the Yukon rely heavily on fish to feed themselves and their families, which makes any warning about mercury exposure especially complicated. “It’s a compounding effect — multiple pressures associated with the rapidly changing Arctic converge to feed into a very uncertain situation.”

But mercury is only part of a much larger story. West is also studying how thawing permafrost and eroding glaciers in Alaska are releasing carbon dioxide. He describes the process as “a slow, enormous fizz,” akin to dropping an effervescent tablet into a glass of water.

The carbon dioxide rises into the atmosphere, intensifying the warming that set the process in motion in the first place. And the effects do not stay confined to the Arctic. Three thousand miles south, USC Dornsife scholars are documenting where similar pressures are surfacing: off the coast of Southern California.

Our Ecosystems Under Pressure

An hour’s boat ride from L.A., where the seafloor plunges to 900 meters, lies the stretch of ocean between the city and Santa Catalina Island that Jed Fuhrman’s lab has been monitoring closely.

Every month for more than 25 years, researchers working with Fuhrman, McCulloch-Crosby Chair in Marine Biology and professor of biological sciences, have sampled the same small area, from the surface down to the ocean floor, to build one of the longest continuous marine microbial records of its kind in the world: the San Pedro Ocean Time-series. Designed to catch signals that shorter studies miss, the project, which is supported by the USC Wrigley Institute for Environment and Sustainability, is now revealing a system under strain.

The spring phytoplankton bloom at this location — which once reliably arrived most years in March — has only occurred a few times over the last 15 years. As the surface water of the ocean warms, it stratifies, trapping nutrients in the deep where sunlight cannot reach them. And less bloom means less food at the base of the food chain.

“Billions of people depend on marine fish for food,” Fuhrman says. “As ocean water warms, we’re likely to see far fewer fish to eat.”

The Oceans at Work

The implications of ocean warming are profound, and USC Dornsife scholars are tracking the consequences, which extend far beyond fisheries. Computational biologist Naomi Levine builds models to understand how the oceans regulate Earth’s climate, and what happens when they begin to falter.

The numbers can be hard to fathom. Microscopic marine plants produce roughly half the oxygen in every breath we take. The oceans have absorbed between a third and a half of all human carbon emissions since industrialization, storing 50 times that amount in dissolved form.

“Without the oceans, we wouldn’t have a livable planet,” says Levine, professor of biological sciences, quantitative and computational biology and Earth sciences. “The oceans are absorbing enormous amounts of heat and carbon. They’re keeping our planet stable and habitable for us. And we are pushing them to their limits.”

Invisible but Essential

In a recent paper, Levine, who holds the Gabilan Distinguished Professorship in Science and Engineering, and her colleagues — including Fuhrman — explained how carbon is transported into the deep ocean and locked away instead of returning to the atmosphere. The mechanism depends on the precise composition of microbial communities — communities that are now themselves under pressure.

Like the health of the human gut microbiome, Levine explains, the ocean’s ability to regulate carbon depends on the balance of bacterial species present. Disrupt that balance and the system becomes less stable. It is holding — for now. “But when organisms are hit with multiple stressors simultaneously,” Levine says, “that’s when we start seeing bigger, more drastic changes.”

While some USC Dornsife scholars are focused on understanding where environmental systems begin to break down, others are working to help vulnerable ecosystems endure — and, where possible, recover.

Turning the Tide

In the Florida Keys, Carly Kenkel, Wilford and Daris Zinsmeyer Early Career Chair in Marine Studies and associate professor of biological sciences, is racing to save coral reefs after a record-breaking 2023 marine heatwave pushed two species to extinction. In partnership with the Mote Marine Laboratory based in Sarasota, Florida, Kenkel’s lab is helping optimize the process of growing heat-resilient corals in nurseries and replanting them in the ocean before Florida’s warming seas destroy the few original survivors — a direct intervention in a system on the brink.

Back in L.A., Professor of Biological Sciences Sergey Nuzhdin is developing climate-resilient kelp strains and exploring large-scale kelp farming. These underwater forests could absorb excess nitrogen from sewage and urban runoff, restoring marine habitat while improving water quality.

A Planet Speeding Up

Taken together, the challenges these researchers are tackling point to multiple ecosystems under mounting pressure. Thawing permafrost, vanishing ocean blooms, intensifying wildfires, rising seas, dying corals and collapsing habitats are not isolated stories. What unites them, West argues, is not just their scale but their speed.

“The pace of change we’re seeing today is far faster than anything documented in the past,” he says. “And the closest parallels are tied to the largest mass extinctions in Earth’s history.”

For generations, America’s landscapes have been quietly chronicling the damage — recording each shift in temperature, each lost habitat, each subtle imbalance. As the nation turns 250, the vital question is no longer whether the signals are there. It’s whether we are willing to grasp them and take action before it’s too late.