美国国家公共电台 NPR To Predict Effects Of Global Warming, Scientists Looked Back 20,000 Years

ARI SHAPIRO, HOST:

Climate scientists are struggling to figure out how a warming planet will affect different ecosystems 1 like forests, swamps and grasslands 3. So researchers looked back at the end of the last ice age to see what might be in store for us. As NPR's Christopher Joyce reports, they suspect some ecosystems could change completely in a century.

CHRISTOPHER JOYCE, BYLINE 4: Much of the Northern Hemisphere was covered by ice sheets 20,000 years ago. Then the Earth started warming up. By 10,000 years ago, it was warmer by about 7 to 12 degrees Fahrenheit 5. Ecologist Stephen Jackson says that makes that period of Earth's history much like what greenhouse gases are doing to the Earth now.

STEPHEN JACKSON: The change over the next 100, 150 years is of similar magnitude globally to what we saw during the last ice retreat.

JOYCE: Jackson works for the U.S. Geological Survey. He and a team of more than 40 scientists examined fossil pollen 6 and vegetation to figure out how that ancient warming affected 7 various ecosystems. The researchers found huge changes after the ice age. In Jackson's neighborhood in Arizona, for example, it's now desert - cactus 8 and shrubs 9 mostly. Fifteen thousand years ago, though...

JACKSON: What we'd see there instead is juniper-pinyon woodland and evergreen 10 woodland - utterly 11 different from the vegetation we'd find here.

JOYCE: So as climate changes, some forests may give way to woody shrubs or grassland 2, or grassland could convert to desert. Writing in the journal Science, the researchers say they can't predict exactly where and how fast these changes will happen. For one thing, the warming now is a lot faster than it was at the end of the ice age.

JACKSON: Instead of that happening over several thousand years, we're cramming 12 all of that climatic change into a century, century and a half.

JOYCE: And their historical record shows a climate going from frigid 13 to warm. Now it's moving from warm to warmer. That may be different. But Jackson says one thing is likely - more predictability, maybe even ecosystems that are totally new. And that poses challenges for forests, wildlands and even fisheries and for people who depend on them.

JACKSON: That's going to create a great deal of chaos 14, ecological 15 chaos out there as they try to adapt and respond to those changes.

JOYCE: These changes are happening now. Some forests in the southwest are dying and being replaced by smaller plants and shrubs. Ecologist David Breshears at the University of Arizona says it's similar to what happened in the past.

DAVID BRESHEARS: These changes are very temperature-sensitive. And I think that's the most important takeaway message because that's what we're dealing 16 with right now I think in contemporary times.

JOYCE: In the journal Scientific Reports, Breshears and scientists in Australia showed how quickly big changes can happen. A heat wave in western Australia in 2011 caused coral bleaching 17 in the ocean as well as tree deaths, damaging insect outbreaks and die-offs of birds - all very different ecosystems, all responding to a warmer environment. Christopher Joyce, NPR News.

(SOUNDBITE OF BLUE IN GREEN'S "RAINY STREETS")