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PRI's Environmental News Magazine

People are Warming the Planet

Air Date: Week of September 29, 1995

For the first time a United Nations panel of leading climate scientists concludes in a draft report that predictions of human induced global warming appear to be coming true. Host Steve Curwood examines some of the research which has led scientists to this conclusion — including data on the earth's recent rash of extreme weather.


CURWOOD: This is Living on Earth. I'm Steve Curwood. Climate change is controversial, because if humans are the major reason behind the gradual warming of the Earth since the Industrial Revolution, then huge changes in our behavior will be needed to respond. And the challenges will be great. Just remember, for example, that the 10-degree warming that ended the last Ice Age 10,000 years ago moved the eastern US coastline in about 100 miles, putting vast territory underwater. So much is at stake. And while the planet warms up, scientists say, our weather will be highly changeable, with more storms, droughts, and other extremes until the climate finds its new balance. Up until recently, the scientific consensus has been around a projection that if humans didn't reduce our emissions of carbon dioxide and other so-called greenhouse gases, the earth would heat up. But this had been only a projection, without solid proof. After all, the average temperature of the Earth has only risen about half a degree since the last century, and that might be due to the Earth's own natural variability in climate. But now the consensus is shifting. The United Nations panel of leading climate scientists says the predictions of human-induced global warming appear to be coming true.

KARL: We now believe that the evidence is much more in favor of man having an impact on the climate system.

CURWOOD: Thomas Karl is a senior scientist at the National Climatic Data Center in North Carolina, and a member of the Inter-governmental Panel on Climate Change. That's the UN body that reviews climate science and recommends policy. In a new draft report that has been circulated on the Internet, the panel says greenhouse gases are almost certainly affecting our climate right now, certain that those changes we're seeing have a unique -

KARL: I think it would be fair to say we're 90 to 95% signature that would not be caused by natural variability alone.

CURWOOD: Thomas Karl is talking about changes in the weather, like the bouts of extreme conditions we've experienced in recent years. The long drought in California, the searing summer of '88, the Midwest flood of '93, this year's rash of hurricanes. Computer models have long predicted increases in these kinds of local weather extremes as carbon dioxide and other greenhouse gases caused the planet to warm up and climate systems to shift. But there's always bad weather somewhere. And only recently have scientists found what the UN draft report calls, quote, "A pattern of climatic response due to human activities, that is identifiable in the climatological record." That record includes a new review of North America's weather patterns by Karl's research group that was recently published in the journal Nature.

KARL: Some of the data that we had available to us allowed us to look at whether or not temperature was becoming either extremely warm or extremely cold, precipitation and drought on either side of the kind of median category, either being very wet or being very dry, whether that was increasing. And we try and put all these factors together; we find that indeed, since the late 1970s, the extremes have increased.

CURWOOD: In fact, the insurance industry has calculated that even allowing for inflation, 12 of the 13 most expensive weather-related disasters in this century have happened since 1987. This kind of weather analysis is part of the new certainty on climate change. But the computer models which help to project the growing extremes have themselves changed. They've gotten better, researchers say, and been put to the test by some major events influencing the global climate. The biggest of these was the 1991 eruption of Mt. Pinatubo in the Philippines, which temporarily put a halt to a 10-year string of record high years.

FIROR: 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, and 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 turn out to be right on the button.

CURWOOD: And today, after a 2-year cooling caused by the Pinatuubo effect, we've returned to the previous pattern of record hot global temperatures. Scientists say that if greenhouse gas emissions continue as expected, the average world temperature will rise about 1 to 4 degrees Celsius, or 3 to 9 degrees Fahrenheit over the next century. And it would rise faster than many natural systems can adapt. Again, Dr. Firor of the National Center for Atmospheric Research.

FIROR: Civilization and plants and creatures are quite sensitive to temperature. Some trees have a very narrow range of conditions 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, rodents, 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 speculate that recent outbreaks of diseases like the Plague, Dengue fever, and the Ebola virus, are due to warmer global temperatures. The final language of the new UN report on climate change is still being debated. But most members of the panel we spoke with say there will be few changes when it finally does come out in December. Even before the report is formally released, governments around the world are already reassessing their policies on climate change. Few industrial nations, including the US, have met the voluntary goals of the 1992 International Climate Change Convention. Some Clinton Administration officials privately acknowledge that meeting the more urgent challenge of a climate that is already changing will call for even tougher measures.



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