Signs of Climate Change Become More Visible; Cause Less Clear

Used to be, the birds returned to Germfask in April.

The red-winged blackbirds and Canada geese showed up first, and the broad-winged hawks came about a month later. Finally, around the first day of summer, the ruby-throated hummingbirds alit in the northern Michigan town after their long flight from South America.

That’s how it was during the Lyndon Johnson administration, anyway. Today, the red-winged blackbirds and Canada geese reach Germfask around the end of March. The broad-winged hawks show up in April. And the hummingbirds arrive before the end of May--more than three weeks earlier than they used to.

If the birds are any indication, spring is coming sooner to Michigan’s Upper Peninsula than it did 30 years ago. Records kept by ornithologist Elizabeth Browne Losey, who has lived on an 80-acre farm in Germfask since the 1940s, show the birds arrived 21 days earlier on average in 1994 than they did in 1965.

Could it be global warming?

“I don’t have a clue,” said Terry Root, a University of Michigan biology professor studying the data Losey collected. “But obviously a lot more research needs to be done.”

From Alaska to Mexico, ecologists are finding provocative signs that global warming already may be altering North America’s flora and fauna. And they worry that next century, when the climate is expected to change more abruptly than it has in at least 10,000 years, plants and animals will be pushed to the limit.

On the West Coast, the range of the Edith’s checkerspot butterfly seems to be gradually moving northward. In the Colorado Rockies and Washington’s Cascades, more vigorous tree growth threatens to cover alpine meadows with forests. Seabirds in California and Oregon have been devastated by a slight warming of the water off the Pacific coast.

In Montana’s Glacier National Park, the glaciers are melting at an alarming rate.

Environmentalists hold these trends up as signs that global warming is already upon us and that the production of greenhouse gases by human beings--mostly through the burning of fossil fuels--is the ultimate culprit.

“The effects of global warming are not merely a future impact in faraway places. The first signs of climate change have been detected and can already be seen in our own backyards,” says a report issued in June by the World Wildlife Fund.

But ecologists are a bit more circumspect.

“Our goal is not necessarily to say that human-induced climate change is responsible as much as to say that things are changing,” said Dan Fagre, a research ecologist with the U.S. Geological Survey’s Biological Resources Division.

Fagre and his colleagues are uneasy about attributing ecological changes to human-caused global warming because North America’s ecological systems have always been in flux. A mere 18,000 years ago--not long in geological time--ice sheets two miles thick covered the entire northern half of the continent. As they melted, plants and animals reclaimed the land the glaciers once covered.

There have been smaller climate fluctuations since then. As recently as 1850, at the end of a period known as the Little Ice Age, temperatures were a few degrees cooler than they are today.

That leaves some ecologists wondering whether the changes they are now documenting are merely the continuation of a natural warming trend that began 150 years ago.

But natural or not, the recent warming trend has a lot of them worried.

If the glaciers of Glacier National Park continue melting at their current rate, for example, they will be gone by 2050. But if climatologists are correct in predicting the next century’s temperature trends, they will disappear by 2030--only 33 years from now.

The glaciers’ disappearance would decrease the amount of cold meltwater in the park’s streams, especially during late summer and early fall. And without a supply of glacial meltwater, some of the streams already are going dry at that time of year, Fagre said, which makes things especially tough on the fish.

Even minor environmental changes can lead to major wildlife disasters, and that’s what keeps ecologists up at night thinking about climate change.

Off the coast of California, where the waters have warmed about 2 degrees Fahrenheit since 1949, several bird species have suffered shocking losses. The population of one species, the sooty shearwater, fell by 90% between 1987 and 1994. Four million birds simply disappeared, according to a paper published this year in the journal Global Change Biology.

How could a slight increase in ocean temperature cause such a catastrophe? By starvation.

The warming of the North Pacific has redirected the ocean’s circulation, decreasing the delivery of cold, nutrient-rich waters to the coast of North America. That lack of nutrients has caused a 40% decline in zooplankton, the shrimp and similar creatures that fish and squid feed on. And sooty shearwaters eat the fish and squid.

“It starts all the way at the base of the food chain and progresses upward,” said Richard Veit, a professor of biology at Staten Island College in New York.

At first, Veit and his fellow biologists thought the sooty shearwaters had migrated northward, into the waters off Oregon and Washington. But when they checked there, the birds were nowhere to be found.

Veit wonders whether salmon populations, which have declined in the North Pacific since the 1970s, may be suffering from the lack of food as well.

“If you look at the pattern of decline of salmon and the pattern of decline of birds, they’re very similar,” he said.

But because many other things have changed for the salmon during the same period--their habitat has been polluted, overfishing has depleted their stocks, and people have built dams along their routes upstream--it’s hard to isolate the damage wrought by global warming.

“I think we can eventually do it,” said Ken Cole, a government ecologist based in Flagstaff, Ariz., “but I’m not ready to commit myself and say that these changes are due to climate change and not these other causes.”

Some of his colleagues are more than ready, however. Last year, a study by Camille Parmesan of UC Santa Barbara showed that the range of the Edith’s checkerspot butterfly, which occupies the West Coast from Mexico to Canada, has shifted northward since scientists began keeping records on its distribution.

“The evidence presented here provides the clearest indication to date that global climate warming is already influencing species’ distributions,” Parmesan wrote in the British journal Nature.

In addition to moving northward, animals and plants are expected to migrate to higher altitudes in response to climate change.

In Rocky Mountain National Park, ecologists are seeing much more robust growth among the highest trees, which extend upward to altitudes of about 11,000 feet. The researchers expect the trees to begin marching up the mountainsides any year now.

The same thing is happening in Washington’s Mt. Rainier and Olympic National Parks, said David Peterson, a professor at the University of Washington and a forest ecologist for the Biological Resources Division.

“What the parks are going to be faced with is [the question], ‘Do we take this change and consider it to be a natural process, or do we mitigate it?’ ” he said.

“Change is natural and normal. The question at this point is: Are the changes that we’re seeing really natural or are they human-caused? And that poses some really tough questions.”