Climate change is melting glaciers, worsening droughts and raising sea levels around the world.

But when it comes to redwood trees — the ancient, iconic sentinels that scientists have worried may be at risk as the planet heats up — global warming may actually be helping, at least for now, according to research to be released Wednesday.

“We’re not seeing any evidence of declining growth rates,” said Steve Sillett, a forestry professor at Humboldt State and nationally known redwoods expert. “In fact, a lot of the sites are exhibiting increasing rates of growth over the last 100 years.”

It may be that the trees prefer warmer temperatures, or that they are benefiting from more sunlight, a longer growing season or even decades of fire suppression. Or they might even be responding well to higher levels of carbon dioxide in the atmosphere.

Nobody knows yet.

But Sillett and other researchers working on an ambitious, four-year study found that growth rates of coastal redwoods and giant sequoia trees in California’s old-growth forests increased during the 20th century, even as other parts of the Earth’s environment — from polar bears to coral reefs — suffered from climate change.

Growth surge

Redwood forests near the California-Oregon border have seen the largest surge in wood production, with growth rates since the 1970s up to 45 percent faster now than at any time in the past 200 years.

The discovery has generated guarded optimism among conservationists.

“Redwoods are an incredibly hopeful story in the midst of seemingly catastrophic environmental change around us,” said Emily Burns, science director for Save the Redwoods League, a San Francisco nonprofit that is sponsoring the research. “They are growing vigorously.”

Water remains a concern, however. A study published three years ago found that the amount of fog in redwood areas along California’s coast has fallen 33 percent over the past century. Scientists were concerned about that, but so far the lack of fog may have allowed more sunlight to reach the trees, said Todd Dawson, a lead scientist on the team and director of the Center for Stable Isotope Biogeochemistry at UC Berkeley.

When it comes to giant sequoias, the biological cousins of coast redwoods that live in the Sierra Nevada, warmer weather may have increased the growing season by reducing the number of days they are under snow. More research is needed in the coming years to test both theories, the researchers said.

Some scientists working on the project are concerned that although the news is good now, conditions could worsen for the trees if rising temperatures cause precipitation in California to decrease significantly over the coming decades.

“There’s a tipping point,” Dawson said. “As we go into warmer and drier times, particularly with snowpacks on the decline — which means less water for giant sequoias — we’re concerned that this growth surge is probably not going to be sustainable.”

$2.5 million project

The researchers are doing groundbreaking work in the world’s tallest and largest trees. Fitted with harnesses and ropes, they have climbed dozens of immense redwoods and sequoias at 13 locations as part of the $2.5 million project. The study’s locations extend from Jedediah Smith Redwoods State Park, near the Oregon border, to Big Sur to the timeless groves of Sequoia National Park in the central Sierra.

The scientists fitted individual trees — many of which were growing before Europe’s medieval cathedrals were built — with sensors to measure temperature, humidity, rain, fog, light, wind and barometric pressure. They used lasers to help measure the heights of trees, complex studies of isotopes to recreate weather from centuries ago, and core samples to learn the ages and growth rates of the trees.

Sillett’s pioneering research climbing redwoods 300 feet tall and higher was featured in the 2007 book “The Wild Trees” by New Yorker writer Richard Preston. As part of the latest study, Sillett discovered the oldest known coast redwood tree in existence, a tree in Humboldt County that is at least 2,520 years old.

“We were way off the trail,” Sillett said. “We stumbled upon this tree. I was like, ‘Oh my god, this tree is big.’ It looked old. It just reeked of age.”

The tree, which had already been growing for 400 years when Julius Caesar was born, is nearly 300 feet tall. Yet it is still significantly shorter than the world’s tallest tree, a 379-foot-tall redwood called “Hyperion” that was discovered in 2006 in a remote corner of Redwood National Park.

Redwoods have been around for 120 million years or more. They once lived side by side with dinosaurs, across Canada, Utah, Montana and Southern California. Today, coast redwoods exist only along a narrow band from Big Sur to the Oregon border. Giant sequoias live only in the Sierra Nevada.

Southern range

Recent modeling by researchers at the California Academy of Sciences shows that if carbon dioxide continues to build in the atmosphere at the current rate — up 30 percent since the mid-1800s because of the burning of fossil fuels — temperatures, rainfall and fog levels at the southern end of the redwood range in Monterey and Santa Cruz counties will become unsuitable to support redwoods by 2100.

Dawson said although the trees are doing well now, the researchers found that redwood and sequoia seedlings die when soil moisture levels fall below 15 percent. So the project, which is seeking new funding, will need to study how seedlings and trees on the edges of the redwood range fare as climate continues to change, he said.

“Redwoods define our state. They define us and our sense of place,” Dawson said. “Why should we preserve them? Why would you preserve a Mozart concerto? They add value to the human condition.”

Paul Rogers covers environmental issues and resources. Contact him at 408-920-5045. Follow him at Twitter.com/PaulRogersSJMN.