Air Date: Week of March 24, 1995

There is a lot of scientific research behind the recent anecdotal observations that many places on Earth are getting warmer. Living on Earth checks in with a number of climate experts who study computer models. They say the findings of a number of research teams are all pointing towards warming.

Transcript

CURWOOD: This is Living on Earth. I'm Steve Curwood.

(Radio static, followed by female announcer: "Global warming may pose more direct threats to humanity than just changing weather patterns and rising sea levels. Many researchers believe as the Earth's temperature increases, the range of deadly tropical diseases will also increase. Computer models suggest that tens of millions..." Fade out; fade in male announcer: "... say another storm is headed for northern California this weekend. At least 15 people died in storm related incidents ... " Fade out; fade in female announcer: "... researchers at the Hopkins Marine station on California's Monterey Bay have found an increase in warm water species of crabs and snails, and a corresponding decrease in cold water species. Comparing animals... ")

CURWOOD: Relentless storms. Raging floods. Changing ecosystems. Shifting seasons. More cholera, malaria, and plague. They may all be signs of a changing global climate. And preliminary evidence suggests that we may be responsible.

(Female announcer: "... one point three degrees in 60 years. The study's authors hope ... ")

CURWOOD: Scientists say it's still too soon to say for sure whether people are changing the world's climate, but the world is getting warmer, from the air at its surface to deep under the oceans. The debate over the human role in climate change is being carried on this month at a meeting in Berlin, where diplomats are plotting out the next steps for international climate policy. Many argue that because the precise human impact is still uncertain, we should be doing everything we can to keep from disrupting the Earth's delicately balanced climate. Stopping the burning of huge tracts of rain forest is not enough, they say. Oil, coal, and gas burning are even more important sources of gases which can warm up the earth. But skeptics also invoke scientific uncertainty. They say before we spend billions to switch away from gas, oil, and coal, we need more evidence that human activity is really warming the Earth. So, with all this uncertainty, what can we say for sure about climate change and global warming? What do we still need to find out? Let's take a look.

(Music up and under)

BROCCOLI: This effect is relatively well-known.

CURWOOD: That's Anthony Broccoli, a climate researcher for NOAH, the National Oceanic and Atmospheric Administration, talking about the greenhouse effect. One thing we do know is that the greenhouse effect is real. It's what keeps the planet warm enough for life. The atmosphere acts like the glass roof of a greenhouse, letting in light from the sun and keeping some of the heat from escaping back into space. Carbon dioxide, water vapor, and certain other chemicals are potent greenhouse gases, and the more of them in the air, the warmer the Earth becomes.

BROCCOLI: We can do calculations that would show that in the absence of an atmosphere, if the Earth reflected as much sunlight back to space as it does now, its temperature would be well below zero. And the fact that our climate is much more comfortable than that is an indication that the greenhouse effect is operating. What people argue about is the extent to which that greenhouse effect can be modified by increases in the greenhouse gases.

CURWOOD: But for Broccoli and most other climate scientists, the argument over how much of an impact additional greenhouse gases will have often masks the broad scientific consensus that adding more of these gases will have an effect.

BROCCOLI: If the question is will greenhouse gases produce a warming of the climate, I am quite confident that the answer is yes. Now, as for the details of that warming, how rapid it will be, whether or not there may be other things going on in the climate system that may partially offset or mask the effects of that warming, I think all of those things are very open questions.

CURWOOD: And they're also very old questions. At least one man linked air pollution to a rise in global temperature a century ago, in 1896.

FIRER: This was done in Sweden by a famous scientist who said, looking out his window, watching the smokestacks evaporating our coal mines into the air, he asked himself what this would do.

CURWOOD: Dr. John Firer is Director of Advanced Studies at the National Center for Atmospheric Research.

FIRER: He did a very simple calculation that said if we doubled the amount of carbon dioxide in the air we would heat the Earth up by an appreciable amount. I think he got a number like 4 degrees Celsius, which interestingly enough is still within the range of what our calculations today show.

CURWOOD: Today, nearly all climate scientists hold pretty close to Gustav Araneus's prediction. They say that if emissions of carbon dioxide continue as expected, some time soon in the next century the average world temperature will rise about 1 to 4 degrees Celsius, or about 3 to 9 degrees Fahrenheit. That doesn't sound like much, and individually most of us wouldn't feel a thing. But Dr. Firer says even a small change could be very disruptive.

FIRER: Civilization and plants and creatures are quite sensitive to temperature. Some trees have a very narrow range of conditions in which they can reproduce. And one of the scary possibilities of a climate change is that forests will need to migrate, as they did as the Earth came out of the last ice age. It took us thousands of years to get out of the ice age. We may be producing a change of similar magnitude in 100 years, and they may not be able to migrate fast enough.

CURWOOD: On the other hand, bacteria, insects, and other disease-bearing organisms can respond quickly, almost instantly, to changing climate conditions. And rising temperatures are an invitation for them to expand their range. That's led some scientists to blame recent outbreaks of diseases like cholera and the plague on warmer global temperatures. Other effects are predicted as well. They include more frequent and more violent storms, and the prospect of catastrophic floods from rising sea levels.

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CURWOOD: We know this: the amount of carbon dioxide in the atmosphere has risen by 30% over the last 2 centuries. And as we've heard, there's a strong connection between the amount of carbon dioxide in the air and the Earth's temperature. But greenhouse gases are only part of the global warming equation. Oceans and clouds, vegetation and ice caps are among a host of other complex forces affecting the climate. The computer models that scientists use to predict climate conditions don't account for these factors very well, and that's contributed to a lot of the uncertainty over just how much of a problem we face. But the computer models are getting better. For instance, Dr. John Firer says they passed a major test after the 1991 eruption of Mt. Pinautubo in the Philippines.

FIRER: Pinautubo was a tragedy for the people who lived around the mountain, but for climate modellers it was a very neat experiment. The volcano put a great deal of sulfur into the stratosphere and added together, there were enough particles to reflect an appreciable amount of sunlight. And so, some of the modellers took a bold step and the moment they had a rough estimate of how much sulfur was in the stratosphere, did predictions. Said: we predict that the climate will cool a certain amount; then it will start to recover and get back on its track of steadily increasing temperature by a certain date and so forth. And so far, those forecasts turned out to be right on the button.