Climate change is altering the American landscape in these and other ways, according to a new report released Tuesday by the Pew Center on Global Climate Change.

The report summarizes the findings of researchers who examined 40 scientific studies that showed links between a warming climate and ecological shifts in plants and animals in the United States. Their analysis found strong links in about half of the studies they reviewed, "a surprisingly high number," said Camille Parmesan of the University of Texas-Austin.

In some places, she said, species are expanding into new territory, particularly along the northern edge of their range. In other areas, wild plants and animals are going extinct. Nature's timing has been thrown off, as plants bloom earlier and animals adjust their natural calendars to adapt to the changes.

Red fox populations are moving northward, for example, pushing arctic foxes out of their homes. Robins are returning earlier to Wisconsin, and frogs are singing their breeding choruses earlier in New York.

"What this report says is that those impacts of climate change are not just in distant lands but are happening right here, right now, and changing life in your own back yard," Parmesan said.

Some of those changes may not have much of an impact. Some species will be able to adapt, and who in Maine wouldn't like an earlier spring? But the findings are important, the researchers said, because they indicate climate change could dramatically alter the U.S. landscape by driving entire species to extinction and contributing to a loss of biodiversity in the natural world.

Scientists say average U.S. temperatures have increased by about 1 degree Fahrenheit over the past century. Precipitation has increased 5 percent to 10 percent.

Hector Galbraith of the University of Colorado-Boulder said the effects of this change are occurring much more rapidly than he expected. He said the study showed him that ecosystems are much more sensitive to climate change than he believed a decade ago.

"Will things get worse? Very likely," he said. "How much worse? That's a matter of conjecture."

Galbraith said the ecological changes could harm efforts to control invasive species because invasives thrive in places where native plants and animals are under stress. It could also have economic repercussions for agriculture, such as "pollination of our crops by insects or pest control in our forests by forest birds," he said.

"If these animals become dissociated from their ecosystems, these economically valuable relationships may be disrupted," Galbraith said.

Parmesan said the "scariest finding" is that the Arctic tundra has gone from being a carbon sink to a carbon source, adding greenhouse gas to the atmosphere instead of taking it out.

"For many thousands of years, Alaska has sucked up quite a lot of carbon in the atmosphere and put it into long-term storage as part of the frozen tundra," she said. "The carbon bank has now turned into a carbon exhaust, so it's now emitting more carbon as winters become warmer and drier and allow dead plant material to decompose."

The report comes on the heels of the Arctic Climate Impact Assessment, a four-year study by 300 scientists released Monday that documented the widespread effects of global warming in the Arctic. That report said that during the past three decades the Arctic has lost 386,100 miles of sea ice, an area larger than Texas and Arizona combined.

The Bush administration has pumped a lot of money into climate change research, but rejects mandatory curbs on greenhouse gases. Bush has also rejected the Kyoto Protocol, saying the large pollution cuts required by the international treaty on climate change would cost nearly $400 billion and eliminate 5 million U.S. jobs.

Eileen Claussen, president of the Pew Center on Global Climate Change, said that in the absence of national action, many states are responding to climate change on their own.

Last year, Maine became the first state to pass a law setting specific goals for the reduction of greenhouse gas emissions. The legislation requires the state to develop an action plan to reduce global warming pollution to 1990 levels by 2010, and 10 percent lower than 1990 levels by 2020.

The state's plan is expected to be released sometime during Thanksgiving week.

Maine has also joined nine other northeastern states in a regional cap-and-trade program focused on reducing power plant pollution, said Sue Jones, energy project director at the Natural Resources Council of Maine. The program is expected to get under way next spring.

Maine has seen its own share of ecological changes that some people attribute to climate change. Maple sap is running a week earlier than it did 50 years ago, sea level has risen 4 inches, and precipitation has decreased 20 percent in much of the state.

"We're seeing different species coming in," Jones said. "We've had invasions of new pests, including Lyme disease-carrying ticks. We think these are attributed to warmer temperature and climate change."