Starving polar bears are eating one another in the Arctic. Flowers are blooming too soon and dying. The ice caps are melting so swiftly that rising water levels will threaten coastal towns as far away as Florida within several decades. These are just a few examples of the dire consequences of climate change supported by a new analysis in Nature that paints a dark portrait of what a warming world will look like in the years to come.

The researchers assessed 829 geologic phenomena—including melting glaciers—along with nearly 30,000 changes in plants and animals (from bird migration patterns to plummeting penguin populations), and found that about 90 percent of them are in sync with scientists' predictions about how global warming will alter the planet.

In the past three decades, average global temperatures have risen about 1 degree Fahrenheit (0.6 degree Celsius) and are projected to jump by about 3 degrees F (1.7 degrees C) by the end of the century, says study lead author Cynthia Rosenzweig, who heads the Climate Impacts Group at NASA's Goddard Institute for Space Studies at Columbia University in New York City. "We've already seen that a relatively low amount of warming," she says, "can result in a broad range of changes."

The unnatural warming spurred on by man-made greenhouse gases, especially carbon dioxide spewed by cars and coal-powered plants, spell trouble for entire ecosystems. In North America alone, scientists have identified 89 species of plants, such as the American holly, that have blossomed earlier in the spring. In Spain, apple trees bloom 35 days ahead of schedule in response to the higher temperatures. Other wildlife, like the insects that use certain plants for food and the birds that feed on the insects, must then move forward their seasonal stirrings and mating patterns to survive.

To try to compensate for this time shift, some birds such as robins, the classic symbol of winter's thaw, are returning to Colorado from their migrations some two weeks earlier than in years past. All these changes can throw a food chain out of whack. To wit: some bird species that arrive before the insects reappear may starve to death.

"Around the world, plants and animals are waking up to an earlier alarm clock than they used to," says study co-author Terry Root, a biologist at Stanford University's Center for Environmental Science and Policy.

The new research, a compilation of the findings of about 80 previous studies from around the world, also confirms that man—not nature—is to blame for global warming. "Overall, this study adds more meat to the IPCC (International Panel on Climate Change) conclusions" that people are causing the world to heat up, says Michael Mann, an associate professor and the director of the Earth System Science Center at Pennsylvania State University.

"This study really speaks to the fact," Rosenzweig says, "that we need to respond and adapt to what's happening."