The songbirds at the feeder outside your window are not the same as they used to be. The goldfinch, the grosbeak and even the ever-present sparrow are all a little bit bigger.

The reason is climate change, according to a new study, which found that 70 bird species, all common to Central California, have evolved a longer wingspan and greater body mass over the past 40 years.

Scientists think such adaptations, in annual increments of less than a tenth of a percent on average, help birds cope with food shortages and stronger storms already triggered by climate change.

"We need to be thinking about things like extreme weather and other ways climate change is going to impact our ecosystems, and those things are not just important for birds," said Nat Seavy, co-author of the bird study and research director at PRBO Conservation Science, a research facility in Petaluma. "They are important for farmers and all sorts of people."

The evidence is just one piece of a new wave of research slowly painting a more vivid picture of what climate change may mean for California. The studies also reflect a new effort by scientists to help the public understand climate change by speaking plainly.

"We struggled mightily to translate these results into lessons that could be useful to policymakers and resource managers," said James Cloern, a biologist at the U.S. Geological Survey in Menlo Park and lead author of a comprehensive new climate study on the Sacramento-San Joaquin Delta.

"We don't want to scare people with this paper. We want to put them in a position where they can start thinking and planning."

Cloern's study marks the first attempt to explain how climate change may affect habitat in an entire estuary, in this case the Sacramento-San Joaquin Delta. The study took seven years and is the most complex Cloern has undertaken in a 36-year career researching the estuary.

Among the projections:

• Extreme water heights that cause flooding – a combination of sea level rise, high tide and storm surge – will switch from rare to routine. Water heights that now occur eight hours per decade at the Golden Gate are projected to occur 1,000 hours per decade by 2050, and worsen thereafter.

• Changes in snowmelt may mean that long periods of flooding become rare in the Yolo Bypass by 2060. Such flooding creates an explosion of insect food that is important to imperiled fish, including salmon.

• Water temperatures lethal to endangered salmon and Delta smelt will become common by 2080.

The findings raise important questions for the public and policymakers.

A Delta restoration and water management plan, now being drafted, could cost $15 billion or more. Some of this money would be spent to create additional habitat for salmon and smelt. Officials and the public will have to decide whether this investment makes sense if climate change is likely to doom the fish decades later.

Many such questions will bedevil society in the years to come.

"I'm not necessarily convinced the extinction of Delta smelt is inevitable," Cloern said. "But we do need to see these projections to get our attention."

One reason, Cloern and other scientists said, is that choices today can prevent undesirable outcomes.

For instance, Cloern's study presents two scenarios: one in which greenhouse gases continue to increase throughout the century, and another in which society halts that growth by 2050.

In the latter scenario, water temperatures deadly to salmon and smelt can be avoided, and long-term flooding of the Yolo Bypass is still a regular event.

But not all aspects of climate change react the same, and other effects may not be avoidable.

Because greenhouse gases emitted by vehicles and industry persist in the atmosphere for decades, a certain amount of glacier melting and sea level rise will be locked in by midcentury. Therefore, Cloern's study projects extreme water heights in either scenario.

Another new study warns that specific tree species in various California habitats have been weakened by the warming trend, making them more vulnerable as climate change continues. Whether that risk can be shaken off if greenhouse gases are brought under control is an open question.

Led by Richard Waring, professor of forestry at Oregon State University, the study found that Douglas fir trees are at risk in California's Central Valley, defined as extending to an elevation of 700 feet.

In the Sierra Nevada, hemlock trees are vulnerable, while in the Cascade Range of the state's northeast corner lodgepole pines are in danger.

Following disturbance such as wildfire or bark-beetle attack, Waring said, these species will have trouble regenerating amid a warmer climate, allowing other species to crowd them out.

"They'll no longer fit into their happy climate environment like they used to," he said. "We're not just talking about the growth of the trees. We're talking about the growth of its competing insects and diseases."

In other words, side effects could include diseases that are new to these trees in their traditional habitats.

One message in the new research is that the effects are not intuitive or predictable. Research in Pennsylvania, for example, found that birds there are getting smaller due to climate change – not larger – likely to conserve energy and due to reduced food supply.

The opposite in California may be due to different climate effects. Warmer weather in coastal California, and a longer growing season, may increase food supply, allowing birds to grow larger.

The changes are small, averaging about 1 millimeter in wingspan over 40 years, but consistent across more than 18,000 birds measured at two netting sites in the Bay Area.

Seavy said these adaptations may allow birds to maneuver better in a growing number of severe storms. A larger body size may allow them to store more calories when food is available, and survive longer when it is not.

No one knows whether these trends will continue or what side effects they might have. For instance, are birds eating more of a particular food that may have ripple effects on other species or on human food crops?

The scientists emphasize there is still a lot of uncertainty in their research. In another five years, Cloern said, the size of the changes they project may be different due to new information and tools.

What's clear is that changes are under way, and the ability to adapt is becoming critical to animals and people.

"It really underlines that climate change isn't as simple as increasing temperatures," Seavy said.

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