From the mountains of Yosemite to the tropical lowlands of Costa Rica,
global warming is forcing animals and plants to move to higher and
higher elevations, searching for climates that have allowed them to
evolve and thrive for millions of years.
The exodus from less tolerable habitats to cooler and more benign
environments has been taking place for nearly a century, according to
scientists who scrambled over rocks and ridges, through steamy rain
forests and up steep volcanic slopes to complete their painstaking
And in a few cases, the moves are taking a toll: Some mountain
animals, left with smaller ranges to forage for food, may face
extinction, while others are up against Darwinian competition as their
new habitats intrude on already-established animal populations.
"These kinds of changes have been going on forever," said James L.
Patton, a biologist at UC Berkeley's Museum of Vertebrate Zoology. "The
only difference is that this has probably happened in our lifetime.
It's the speed with which these changes are taking place that gives one
As the pace of global warming quickens, change is everywhere: from
glaciers melting in Greenland, to ice shelves crumbling in Antarctica,
to coral reefs dying in tropic seas - and now to animal and plant life
in many parts of the world.
In a report appearing today in the journal Science, Craig Moritz,
also of the Museum of Vertebrate Zoology, Patton and their colleagues
describe how they surveyed 28 species of mammals studied by the late UC
ornithologist Joseph Grinnell beginning in 1914. They covered many of
Grinnell's sites from the San Joaquin Valley across all of Yosemite,
over the crest, and down to Mono Lake and then compared the results.
Their report is appearing with another one on the effects of climate
change in Costa Rica by an international group headed by Robert K.
Colwell, an entomologist at the University of Connecticut who was
formerly also a UC Berkeley scientist.
The impacts of warming
Moritz and Patton note that since Grinnell completed his work, the
central Sierra has seen continuous warming, with nighttime low
temperatures averaging 5 degrees Fahrenheit higher than they were 90
years ago. During the same period, more than half of the species he
studied have shifted their ranges upward by as much as 1,600 feet, the
Many of the others, Moritz and Patton said, stayed put in ranges
that shrank over time, largely the result of human development rather
than climate change.
The California vole, the California pocket mouse and the western
harvest mouse, for example, have all increased their ranges by moving
up-slope, while the bushy-tailed wood rat and Allen's chipmunk remained
at lower levels but their ranges have diminished, the Berkeley
Another chipmunk, the alpine species, saw its range shrink before it
moved upward more than 2,000 feet seeking a friendly climate, Patton
said. Ninety years ago, that same species of alpine chipmunk was common
in lodgepole forests below 7,800 feet, but Patton said he found none
living lower than 9,600 feet. As a result, he said, it may now face the
risk of extinction because of its diminished range.
Similar changes are also endangering plant and insect species in
some of the warmest places on Earth, according to the international
survey team headed by Colwell, an evolutionary biologist.
In the tropics the climate has warmed by nearly 1.5 degrees
Fahrenheit since 1975, Colwell's report in Science notes, and climate
models for the tropics indicate it could get hotter by nearly an
additional 6 degrees before the end of the century.
Working their way up the forested slopes of Volcan Barba in Costa
Rica - from sea level to the volcano's summit at nearly 10,000 feet -
Colwell and his team of scientists surveyed the ranges of 1,902
different species of insects and plants, including moths and ants,
orchids, mosses, ferns, fungi and the shrubs and bushes that live
beneath forest canopies.
Trouble ahead for insects
Based on their observations, the scientists foresee trouble ahead:
As the climate warms, even in the wet tropics, Colwell said, the ranges
of many insect species will become more isolated in their higher
Some species now living part way up the volcano will have to move
their ranges as much as 2,000 feet higher if the climate heats up by as
much as 6 degrees, and that will put them into wholly new environments
facing competition that evolution hasn't equipped them to face, the
At the same time, species already living near the volcano's summit
will find themselves with nowhere higher to move. In Colwell's words,
they'll face "mountaintop extinction" as the climate warms even more.
In the tropical lowlands, little opportunity exists for plants or
animals to escape future increases in temperature by migrating either
north or south - it's all hot everywhere. So as temperatures increase,
according to Colwell's report, about half the species the Costa Rica
team studied will disappear - unless they retained the genetic
tolerance for greater heat that their ancestors possessed some 55
million years ago when the world was far hotter than it is now.
The others may seek new habitats in wetter regions that are at least
somewhat cooler than where they live now, but even then the warming
trend will increase the dangers from drought and forest fire.
So the future looks tough all over.