TOM BEARDEN: A decade ago, Camille Parmesan was spending months in the California back country doing scientific research on the biology of butterflies. She found something she wasn't looking for.
CAMILLE PARMESAN: I was really working on more basic questions of their evolution of diet and their behavior and looking for food plants and what-not, and it was over the years as I was doing this, it became very obvious that they're extremely sensitive to climate, particularly temperature.
They can only fly at very certain times of the day where you've got sunshine and the right air temperatures. If they get too hot, they stop flying. If they get too cold, they stop flying.
TOM BEARDEN: She learned those things in the early 1990s, about the time the global warming debate first began. That debate continues to this day -- if it's real, if it's caused by humans, and whether humans can do anything about it.
With her studies on butterflies, Parmesan became was one of the first scientists to study how changing climate might effect wildlife populations. When she studied one species, the Edith's Checkerspot Butterfly, up and down the West Coast, a pattern emerged.
States where the butterflies had once been but were now extinct were grouped toward the south. When she looked at places where the butterflies still lived, there was a subtle but noticeable shift to the North.
After factoring out other causes, Parmesan tentatively concluded the butterflies were gradually and almost imperceptibly moving north in response to a slight rise in global temperature.
CAMILLE PARMESAN: If something accidentally gets blown out of its normal range, the normal range for the species, it just dies. But with climate warming now, you get those same events happening, and when that female plops down and lays her eggs, now it has a chance of surviving.
And so over a five or ten-year period, you can get several populations starting. Once you get that, you've got the whole species' range having shifted.
TOM BEARDEN: A few years later, when Parmesan and her associates looked at hundreds of studies of butterflies, the same pattern showed up.
In England, the speckled wood butterfly had lived mostly in the south in the mid-20th century. By the end of the century, most had moved to the English midlands. In Sweden and Finland, the silver-washed fritillary used to live here. Now it lives here as well.
Not all the butterfly species followed that pattern. Some moved south; some didn't move at all. A clear majority, though, had moved north, and that raises questions about the negative impacts of global warming.
CAMILLE PARMESAN: The question is, how many species are going to be able to just move north and live perfectly happily, and how many are going to be obstructed, either because they are such habitat specialists that there just isn't any food for them to the North or they're being delayed because they are dependent on some plant; the plant has a slower rate of change, therefore, they can't move north.
TOM BEARDEN: Early this year, an international team of ecologists completed a computer study that went much further in predicting the consequences of global warming.
Their study made headlines around the world. It estimated that by the year 2050 as many as one million species could be on their way to extinction due to global warming.
Lee Hannah, a senior fellow at Conservation International, was one of the authors. The team looked at 1,500 plants and animals and mapped the precise areas where each could live in the present climate. Then they estimated how the climate might change by 2050.
LEE HANNAH: All species depend on climate for their survival, and each species has climatic conditions that it prefers. You'll see that this is the preferred climate of this species, and we use the climate projections to project where it might go in the future, and that's this dark yellow area.
And you can see it's both contracting and moving up slope. We're strongly seeing the up-slope movement as things go from a lower elevation where it's warm now to trying to maintain that same temperature envelope and maintain the other climate variables that it prefers in the future.
TOM BEARDEN: And at some point, it can't go... there's no place to go, there's no place to go higher.
LEE HANNAH: Right.
TOM BEARDEN: The researchers matched that reduced living space to a well-known ecological law -- The bigger the piece of land, the more different species live on it. And the corollary -- less land area means fewer species.
They concluded that hundreds of thousands of species would lose so much living space that many stood a much greater chance of eventually going extinct. How much greater? The number varied, depending on how much the climate changed.
LEE HANNAH: Species risk of extinction was quite significant with climate change-- in double digits in almost all regions and with the mid-range scenario extinction risk of about 25 to 30 percent.
TOM BEARDEN: Which is an enormous number?
LEE HANNAH: It's a very large number. It's important to notice that that number isn't expected by 2050. It's the climate changes that would occur by 2050 that would eventually lead to that level of extinction.
TOM BEARDEN: Still, as big as the number is, it's only the product of number crunching. The researchers did no new fieldwork and made no new observations. The authors admit they don't know exactly how many species might go extinct or when. What they do find is that the overall trend of the numbers is disturbing.
LEE HANNAH: We've called them a first pass or a first run "look at this" issue. And that means the early projections are a reasonable first guess at what this might mean for species on the planet.
TOM BEARDEN: Daniel Botkin thinks the computer modeling used in the study was too simplistic.
DANIEL BOTKIN: Quantitatively not useful, and based on a false premise which is not useful.
TOM BEARDEN: Botkin taught environmental science at the University of California, Santa Barbara , wrote a book about forest ecology, and even developed a computer program to predict growth patterns in forests over many years.
He says species are adaptable and the study doesn't prove plants and animals will go extinct if their living space shrinks.
DANIEL BOTKIN: Shrinking area will have an effect, but having a small area or a smaller area of a certain size doesn't necessarily mean you have by necessity dropped an exact number of species.
That's not to say that there isn't going to be an effect on species of global warming or that as you reduce area and reduce habitat there won't be problems. But as a prediction, in terms of the number of species, this paper is, I believe, misleading.
TOM BEARDEN: Some have argued that this is essentially a computer modeling study and that the computer models themselves don't really accurately reflect the ecosystem itself.
LEE HANNAH: We're trying to look at what happens in the future, and of course those efforts can never be perfect. These models are some of the most sophisticated tools we have to address this issue. That's why we think it's important to take their results very seriously.
TOM BEARDEN: Botkin says he does take the impact of global warming on species seriously, but he thinks the right approach is to work it out slowly, one species at a time.
DANIEL BOTKIN: Well, the approach I like is the approach that I've used myself, where you look at individual species and use them and for themselves or as types of species and then look at specific effects of global warming.
My concern is that we haven't looked enough at the effects on living things. This has been a very small part of any funding and any effort, and yet effects on life is what really matters about global warming.
TOM BEARDEN: Camille Parmesan is continuing her studies in the lab, not the field. She says biologists spent a lot of the 20th century worrying about a different threat to wildlife -- the loss of habitat caused by advancing civilization. So they were slow, she says, to respond to climate as a different threat.
CAMILLE PARMESAN: People have shifted from thinking of habitat loss as being the major problem. Well, it's the major problem right now, but if you're trying to save something for your grandchildren, something over the next 100 years, then climate change turns out to be a bigger problem.
TOM BEARDEN: Parmesan and other scientists hope their findings can help guide policy-makers on the best response to a changing climate in the future.