Rising global temperatures are taking their toll on Puget Sound, as less mountain snow funnels less freshwater into estuaries, rising oceans transform salt marshes, and changes to the food web alter life for everything from lingcod to orcas, a new study says.

The report released yesterday, the first serious attempt by University of Washington scientists and the state to gauge the impact of global warming on Puget Sound, suggests that climate change will continue to echo across the ecosystem, upsetting links between plants and animals and complicating efforts to manage the threat of a growing human population.

"It's not like we're going to wake up tomorrow and everything will be dead," said Jan Newton, a UW oceanographer who contributed to the 35-page report by the Puget Sound Action Team, a state agency that monitors the Sound's health.

"But we also know that when organisms experience catastrophe, it's most often because they're assaulted by more than one problem at a time. The sooner we recognize that things are under pressure because of climate change, we can look at the stressors we can do something about."

The state has issued biannual reports in recent years on the health of Puget Sound. Until yesterday, however, no one had created a cohesive picture from all the latest climate science.

"It's frightening and baffling," said Brad Ack, executive director of the Puget Sound Action Team. "I was surprised by how much we've already experienced — some of the most significant change in North America. What's less certain is how it will all play out."

Already, the region's signature body of water is warming faster and its water levels are rising quicker than waters in many other parts of the world, the report says.

While average global temperatures rose 1.1 degrees Fahrenheit during the 20th century, Northwest winters have warmed 2.7 degrees since 1950, in part because of cycles in ocean conditions. Scientists don't know how much of that to attribute to global warming.

Meanwhile, water levels in south Puget Sound are expected to increase 1.3 feet by 2050, higher than in most areas of the world because changes in Pacific Ocean wind patterns drive more seawater into Puget Sound. The change will be compounded because geological factors are causing land in the Olympia and Tacoma areas to sink about an inch every 12 years.

Runoff from the 10,000 rivers and streams that spill into the Sound is already shifting, according to the report: About 13 percent less freshwater flows to Puget Sound now than in 1948, and snowmelt is coming an average of 12 days earlier.

With lower snowfall, more of the Northwest's precipitation comes as rain, the study says, so flooding is likely to increase because the water isn't held in mountain snowpack. And that could affect how sediment and debris is washed into the Sound.

Such simple-seeming swings can have wide impacts.

Rising water increases erosion, and also threatens the habitat of kelp and other grassy plants that incubate dozens of species of fish and vegetation that can't survive without it.

Warming water could increase harmful algae blooms, which can contaminate shellfish. When those blooms die, they suck oxygen out of the water, causing "dead zones" like an area in Hood Canal where thousands of fish have been killed.

Lower water levels in rivers and streams already have hurt salmon runs. But when the largest volumes of freshwater come earlier in the year, it can compound problems for many other creatures in the Sound, said Nate Mantua, a professor of atmospheric sciences at UW's Joint Institute for the Study of the Atmosphere and Oceans.

Rivers flush plankton and other nutrients into the Sound, as well as helping to cool estuaries and moderate their salt levels. That helps determine how much food wells up from the cold, dark bottom.

But as the volume and timing of those river flows change, the tiny creatures that eat the plankton may still emerge when they always have, which means they may miss their primary food source.

In turn, that means those tiny creatures may not be available to be eaten when herring or other bottom fish spawn, or when shorebirds arrive during migration.

What's worrisome to the scientists is that even if one or two of those factors is altered, the whole food chain would have to adjust, potentially changing the diversity of fish and mammals in the Sound.

"Usually what we find is that rapid change favors the generalist; if you rip out your lawn, what repopulates it first ... dandelions, right?" said Phil Mote, a climatologist with UW's Climate Impacts Group who participated in the study. "So stress could push some more specialized species over the brink and make it easier for species that can live anywhere, many of which are invasive species."

But all of the complicated functions are still poorly understood.

"It's like trying to predict the economy," said Newton, the UW oceanographer. "We have tools and models, but there's just a lot we don't know yet."

For example, eelgrass, an important nursery for fish, may actually benefit from changes in freshwater flows. And when plankton blooms come at different times, many species lose, but others win.

"Climate change is shifting that whole balance," said Amy Snover, a research scientist with UW's Climate Impacts Group. "What happened in the past is no longer going to be a way to judge what will happen in the future."

Even as scientists seek to better predict the future, Ack said politicians and governments should consider broader implications when managing everything from shorelines to water supplies, salmon and hydropower.

"I'm committed that every time we have a discussion about these issues, we're asking how climate change fits in," he said.

Craig Welch: 206-464-2093 or cwelch@seattletimes.com