太陽亮度變化太微弱，不足以解釋地球全球暖化現象
Changes in Solar Brightness Too Weak to Explain Global Warming
About the article Title:
"Variations in solar luminosity and their effect on the Earth's climate."
Authors: P. Foukal, C. Frohlich, H. Spruit, and T.M.L. Wigley
Publication: Nature, September 14, 2006
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BOULDER—Changes in the Sun's brightness over the past millennium have
had only a small effect on Earth's climate, according to a review of
existing results and new calculations performed by researchers in the
United States, Switzerland, and Germany.
The review, led by Peter Foukal (Heliophysics, Inc.), appears in the
September 14 issue of Nature. Among the coauthors is Tom Wigley of the
National Center for Atmospheric Research. NCAR’s primary sponsor is
the National Science Foundation.
“Our results imply that, over the past century, climate change due to
human influences must far outweigh the effects of changes in the Sun's
brightness,” says Wigley.
Reconstructions of climate over the past millennium show a warming
since the 17th century, which has accelerated dramatically over the
past 100 years. Many recent studies have attributed the bulk of 20th-
century global warming to an increase in greenhouse gas concentrations
in the atmosphere. Natural internal variability of Earth’s climate
system may also have played a role. However, the discussion is comp-
licated by a third possibility: that the Sun's brightness could have
increased.
ftp://ftp.ucar.edu/communications/activity-02-high.jpg
In this image from an active solar period in March 2001, colors are
shifted to highlight the contrast between sunspots (black and dark red)
and the faculae that surround them (bright yellow). During the peak of
the 11-year solar cycle, the expansion of faculae outweighs the dark-
ening from increased sunspot activity. The result is a net increase in
solar brightness. (Image courtesy NASA.)
The new review in Nature examines the factors observed by astronomers
that relate to solar brightness. It then analyzes how those factors have
changed along with global temperature over the last 1,000 years.
Brightness variations are the result of changes in the amount of the
Sun’s surface covered by dark sunspots and by bright points called
faculae. The sunspots act as thermal plugs, diverting heat from the
solar surface, while the faculae act as thermal leaks, allowing heat
from subsurface layers to escape more readily. During times of high
solar activity, both the sunspots and faculae increase, but the effect
of the faculae dominates, leading to an overall increase in brightness.
The new study looked at observations of solar brightness since 1978 and
at indirect measures before then, in order to assess how sunspots and
faculae affect the Sun’s brightness. Data collected from radiometers
on U.S. and European spacecraft show that the Sun is about 0.07 percent
brighter in years of peak sunspot activity, such as around 2000, than
when spots are rare (as they are now, at the low end of the 11-year
solar cycle). Variations of this magnitude are too small to have
contributed appreciably to the accelerated global warming observed
since the mid-1970s, according to the study, and there is no sign of a
net increase in brightness over the period
To assess the period before 1978, the authors used historical records
of sunspot activity and examined radioisotopes produced in Earth's
atmosphere and recorded in the Greenland and Antarctic ice sheets.
During periods of high solar activity, the enhanced solar wind shields
Earth from cosmic rays that produce the isotopes, thus giving
scientists a record of the activity.
The authors used a blend of seven recent reconstructions of Northern
Hemisphere temperature over the past millennium to test the effects
of long-term changes in brightness. They then assessed how much the
changes in solar brightness produced by sunspots and faculae (as
measured by the sunspot and radioisotope data) might have affected
temperature. Even though sunspots and faculae have increased over the
last 400 years, these phenomena explain only a small fraction of global
warming over the period, according to the authors.
Indirect evidence has suggested that there may be changes in solar
brightness, over periods of centuries, beyond changes associated with
sunspot numbers. However, the authors conclude on theoretical grounds
that these additional low-frequency changes are unlikely.
“There is no plausible physical cause for long-term changes in solar
brightness other than changes caused by sunspots and faculae,” says
Wigley.
Apart from solar brightness, more subtle influences on climate from
cosmic rays or the Sun's ultraviolet radiation cannot be excluded,
say the authors. However, these influences cannot be confirmed, they
add, because physical models for such effects are still too poorly
developed.
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太陽亮度變化太微弱，不足以解釋地球全球暖化現象
根據美國、瑞士與德國太陽物理學家Peter Foukal等人的最新研究結果顯示：
太陽過去1000年來的亮度變化，對於地球氣候的影響非常小；因此地球的全球
暖化現象，主要是由人類的活動所造成。相關論文發表在2006年9月14日出版
的自然（Nature）期刊中。
綜觀地球過去1000年的氣候變化，從17世紀開始就開始呈現逐漸暖化的現象，
而這個暖化現象在最近100年更是急遽增高。許多研究都顯示暖化主要肇因於
溫室效應氣體釋放到大氣中的結果；地球本身的自然變化也有一些影響。另外
還有一些人提出第三種理論：太陽的亮度增加可能對地球氣候暖化也有貢獻。
http://www.tam.gov.tw/news/2006/200609/activity-02-high.jpg
黑子就像拴塞一樣，會阻擋太陽內部的熱量傳遞到太陽表面，因而使表面變暗
；然而這些被堵住的熱能會從太陽黑子周圍洩漏而出，形成光斑。在太陽活動
最活躍的時期，黑子和光斑的數量都會增加。上圖是2001年3月太陽表面最活
躍時期拍攝的影像，黑色與暗紅色部分為太陽黑子，太陽黑子周圍則有大片的
明亮光斑（faculae）環繞(Image courtesy NASA) 。但基本上，太陽愈活躍
，光斑出現的比例愈高，使太陽變得明亮的程度，比大量黑子出現、使太陽亮
度減低的效應還高。
Foukal等人分析1978年以後直接觀測的太陽亮度，和1978年以前的資料則以間
接的其他方式測量，如格陵蘭和南極冰原中存藏的同位素含量等。分析結果顯
示，在11年太陽黑子活動週期中，太陽亮度在活動達到最高的程度時，只比活
動最低點時平均亮了0.07％而已。這樣的亮度變化實在是太過於微弱，不可能
對1970年代中期以後全球加速暖化的現象有明顯的影響，而且不同週期的太陽
淨亮度也沒有增加的趨勢，換句話說，每一次活動週期中的太陽亮度都差不多。
不過，這想探討僅限於太陽亮度的影響，並未將太陽所發出的紫外輻射或宇宙
線的想囊括在內。目前對於紫外輻射或宇宙線的物理模型還不夠成熟，因此對
於這方面的探討也比較少。
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來源：UCAR
http://www.ucar.edu/news/releases/2006/brightness.shtml
TAM
http://www.tam.gov.tw/news/2006/200609/06092001.htm
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