Sun’s warming is global:

The twin solar images glared from the screen in the Harvard-Smithsonian Center for Astrophysics’ auditorium, green tinged with yellow, swirls of fire erupting from the surface.

One image had more fire swirls, showing the sun during a period of maximum solar activity. The second showed a quieter sun, during a solar minimum.

Lit up by the image were the faces of about 150 community members who packed the Center for Astrophysics’ (CfA) Phillips Auditorium to hear CfA research astrophysicist Sallie Baliunas talk about recent findings linking solar activity to global climate.

The research, conducted with colleague Willie Soon, links cycles of sunspots and outbursts of solar activity with long-term changes in terrestrial climate.

The talk came just weeks after their paper on the subject was published in the journal of Energy and Environment. With human-induced global warming a hot topic, their findings of the sun as a potential significant natural factor in global warming generated a lot of reaction, according to CfA Director of Public Affairs David Aguilar.

“Ten days ago we sent out a news release; our phones have not stopped ringing,” Aguilar said.

The talk was part of the Center for Astrophysics’ monthly Observatory Night lecture series, which is open to the public and followed by a session of sky watching through telescopes on the CfA roof.

During her talk, Baliunas took the audience on a tour through the ages, from the warmest period known, the Mesozoic era of the dinosaurs, about 250 million years ago, through the Ice Ages and into recorded human history.

Though records of solar activity are not as complete as the Earth’s climatological history, Baliunas and Soon assembled four centuries of telescopic data along with information gleaned from tree rings and ice cores dating back thousands of years.

They found correlations between periods of high solar activity with warm periods on Earth, like the Medieval Warm Period from 800 to 1300 – when the Vikings settled Greenland and Newfoundland. Similarly, they found a reduction in solar activity during cooler periods, like the Little Ice Age from 1300 to 1900.

“Changes in the output of the sun, in some measure, are linked to changes in temperatures on Earth,” Baliunas said. “The sun seems to be one of the factors, but not the only one.”

Using charts and dramatic images of the sun and stars, Baliunas took the audience through the history of solar exploration and laid out the evidence as she and Soon saw it.

The audience seemed enthusiastic about the subject, asking questions during a question-and-answer session and then clustering around Baliunas and Soon, who was present for the talk, with more queries when the program concluded.

“It was a great learning experience,” said Maria Hamill of Boston, who came to the talk with several friends.