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Launch of SpaceShipOne
Watch the hair-raising flight of SpaceShipOne during the first of two launches needed to win the $10 million X Prize. The craft experienced a major rolling motion and early engine shutdown. (3min 40sec file)
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The roll close up
This high bandwidth clip focuses on the unplanned rolling motion that SpaceShipOne saw during its engine firing. (1min 25sec file)
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Reentry descent
SpaceShipOne feathers its wings for a "care-free" reentry into Earth's atmosphere that doesn't require a precise angle of attack. (2min 59sec file)
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SpaceShipOne landing
SpaceShipOne glides to landing on the runway at Mojave airport under the control of astronaut Mike Melvill. (1min 41sec file)
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Melvill emerges
A truck tows SpaceShipOne from the runway to the spectator viewing spot where Mike Melvill climbs out for welcoming by Burt Rutan and others. (2min 01sec file)
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Post-flight speeches
Hear from Mike Melvill, Burt Rutan and others during post-flight speeches on the runway at Mojave airport. (6min 40sec file)
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X-43A test
NASA's X-43A research craft and its Pegasus rocket booster complete a captive carry test flight aboard a B-52 launch aircraft. (1min 48sec file)
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See the KSC damage
See damage to the Vehicle Assembly Building, the Saturn 5 Center and other facilities at Kennedy Space Center caused by Hurricane Jeanne. (4min 31sec file)
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Cape damage report
Jim Kennedy, director of the Kennedy Space Center, and Col. Mark Owen, 45th Space Wing commander, hold a news conference on Monday, Sept. 27 to provide a preliminary report on damage from Hurricane Jeanne at KSC and Cape Canaveral Air Force Station. (49min 30sec file)
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Hurricane Jeanne
Cameras aboard the International Space Station captured these views of Hurricane Jeanne on Saturday, Sept. 25 as the storm approached Florida. (3min 59sec file)
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Station news briefing
International Space Station program manager Bill Gerstenmaier holds a news conference Sept. 24 to discuss problems with the oxygen generation system and Expedition 10 launch preparations. (44min 06sec file)
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Evidence shaky for role of Sun in past climate changes
Posted: September 30, 2004

Computer models of Earth's climate have consistently linked long-term, high-magnitude variations in solar output to past climate changes. Now a closer look at earlier studies of the Sun and Sun-like stars casts doubt on the evidence of such cycles, their intensity, and their possible influence on Earth's climate. The findings, by a solar physicist and two climate experts, appear in the October 1 issue of the journal Science.

The authors write, ". . .long-term irradiance variations used in climate models in the past decade may be a factor of 5 [five times] larger than can be justified. The full impact of this changed outlook on attempts to explain past climate variations and estimates of climate sensitivity to external forcing remains to be seen."

Scientists have attributed observed climate changes to a combination of natural variations and human activities. Computer models of global climate reproduced an observed global warming during the first half of the 20th century when two solar influences were combined: a well-documented 11-year sunspot cycle and the decades-long solar cycles now in dispute. A more pronounced warming observed during the century"s late decades is attributed to greenhouse gases accumulating in Earth's atmosphere and is not part of the new study.

"Removing these long-term solar cycles from the input to climate models takes away about a tenth of a degree [Celsius] of the early 20th century warming," says Tom Wigley, a climate expert at the National Center for Atmospheric Research (NCAR) and a co-author of the paper. "Although this makes it harder to explain the warming, the difference falls within the noise range for natural variability. This suggests that other influences on past climate changes may play a greater role than the solar one."

Peter Foukal of Heliophysics Inc., Gerald North of Texas A&M University, and Wigley authored the paper. The National Science Foundation, NCAR's primary sponsor, and NASA funded the research.

Climate models have also linked long-term changes in solar energy to preindustrial climate changes, such as the so-called Little Ice Age of the 17th and 18th centuries.

"Removing or reducing the long-term solar influence is most important for understanding the Little Ice Age," says Wigley. Although this cooling occurred primarily in Europe, it has commonly been attributed to a lethargic Sun.

The authors scrutinize a considerable range of previous evidence related to solar cycles, including:

  • brightness variations of selected stars
  • whether the selected stars are actually Sun-like
  • the long-term relation between stellar brightness and magnetic field
  • the magnitude of the supposed solar variations
One of the earlier studies mentioned by the authors examined other stars to observe brightness changes at various stages, with the idea that similar activity occurs on the Sun. Researchers have questioned whether those stars' mass, age, and chemical composition were truly Sun-like.

The 11-year sunspot cycle is not questioned in the Science paper, but its effect alone is "probably too little for a practical influence on climate," the authors write. They also briefly consider possible influences of ultraviolet and cosmic ray fluxes in Earth's climate.

The authors allow that long-term brightness variations of the Sun may exist, but more convincing evidence is needed, they say. New technologies now available can provide better data for understanding Sun-climate relations, they conclude.

Opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.