Dr. Sallie Baliunas of the Harvard-Smithsonian Center for Astrophysics is one of the world's experts on the sources of climate change. Baliunas argues that natural variations in the sun's energy closely correlate with known changes in Earth temperatures over the centuries. Baliunas believes such natural variations account for nearly all of the global warming trend of the 20th century, while human impact has been at most "tiny." James Glassman, American Enterprise Institute fellow, long-time host of the late, lamented Techno-Politics, and publisher of the Website TechCentralStation, recently interviewed Baliunas. We reprint a brief edited excerpt here. To see the full interview go to www.techcentralstation.com.

James K. Glassman: Dr. Baliunas, we've heard that temperatures have increased on Earth over the last century. Were temperatures stable before that?

Dr. Sallie Baliunas: The temperature of the Earth has increased over the last 100 years. . . . The warming began early in the 20th century, late in the 19th century. But before that, there was a very long, protracted cooling that began in the 14th century that continued to the mid-19th century--a 500-year relative cold spell called the Little Ice Age. Before that, 800 or 1,000 years ago--the early part of the millennium--the temperature was even higher than today, worldwide . . . .

Glassman: How can you tell?

Baliunas: The thermometers go back only about 100 years or so over some substantial portion of the Earth. Then we have to rely on other records. . . . For example, growth of tree rings is retarded during cold times usually and then is more advanced during warm times. . . . Glaciers advance and retreat, mountain glaciers, polar glaciers. Coral growth rings tell us about the temperature of the ocean.

Glassman: If there was global warming before the 20th century . . . what caused it?

Baliunas: When the sun's magnetism is strong, the sun's energy output is higher and the Earth is warmer. . . . We measured that carefully over the last 20 years with satellites from the Earth, and we measured it indirectly going back 400 years, 1,000 years, and 10,000 years.

Glassman: Now, have you actually correlated the activity of the sun, this magnetism that you're talking about, with the rise of temperatures on Earth?

Baliunas: Yes, the correlation is very strong. For the temperature records going back on Earth, we can reconstruct the Northern Hemisphere about 250 years or so. And the ups and downs of temperature match almost exactly the ups and downs and change in magnetism, and so, the energy output of the sun. . . .

Glassman: Has there been solar activity over the last hundred years that would correlate with the temperature on Earth?

Baliunas: Yes, it correlates almost exactly with the temperature on Earth. The sun is as magnetically active as it's been in our direct telescope records of the sun since the days of Galileo. So the magnetism of the sun has been rising gradually, and it was especially sharp early in the 20th century, coincident with this rise in temperature on the Earth.

Glassman: Now there were declining temperatures from the 1940s through the mid-'70s. Was there a lack of magnetism?

Baliunas: Yes, from about the 1930s, the 1940s, the sun's magnetism waned a little bit and has since picked up a little bit.

Glassman: What you're saying is that solar activity is causing global warming?

Baliunas: We are looking to find all the causes of natural change of the climate of the Earth, the sun being one of them. That way we can subtract out the natural changes and look for the human signal. We see, essentially, no signal of human activity. Most of the changes that we see line up with the changes in the sun. Now there's some uncertainty, so there may be a human signal. But if there is, it's quite tiny. . . .

Glassman: I have read articles in the New York Times and elsewhere about the observation of some icebreakers saying, "Wow, there doesn't seem to be as much ice up here . . . "

Baliunas: No, those observations have been overturned. . . . Ice can change for reasons other than temperature. It can change because precipitation's changed. Some of the models, in fact, say that sea ice should be growing as you warm a little bit because it's so cold at the North Pole that you warm a little bit and get more precipitation.

Glassman: How much warming have we actually seen in the last 100 years?

Baliunas: There's been about a half a degree centigrade or a degree Fahrenheit warming. Most of that warming occurred early in the century, before the greenhouse gasses by human activities were added to the atmosphere. . . .

The acid test of all this is the last 22 years of satellite measurements made of the lower layer of air of the Earth. That layer of air should be warming quite rapidly. It's where the carbon dioxide greenhouse effect should be taking place. That layer has not seen a big warming trend. It's seen ups and downs, but there's been no net trend. That layer of air has to warm first according to the (global warming) models. Then it, in turn, warms the surface. Now we've seen a little bit of warming of the surface, but it can't be caused by that carbon dioxide effect in that atmospheric layer, which has no warming. You can't bypass the lower layer of air and warm the surface by carbon dioxide effect. . . .

Glassman: Would you say, in general, that at this point the science is unsettled?

Baliunas: The science altogether is unsettled, but we know for sure that the models that make the predictions into the future are exaggerating the warmth. . . . The fact that we stop emitting carbon dioxide will do nothing to change the course of the climate. . . .

James K. Glassman is a resident fellow at AEI.