Posted on 09/13/2006 12:32:39 PM PDT by cogitator
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 complicated by a third possibility: that the Sun's brightness could have increased.
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.
The University Corporation for Atmospheric Research manages the National Center for Atmospheric Research under primary sponsorship by the National Science Foundation. 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.
"The pirate theory seems plausible enough.'
Then join us matey, yah hears the call of the sea dont ya?
Or are ye a lilly livered landlubber?
Fetch yer cutlass and watch the might of buccanneers tame the beastie global warmin.
I get seasick.
Muller does not factor in changes in Solar output.
His analysis deals mainly with the impact of changes due to the in the precession of the earths orbit as it intersects in and out of the accretion disc of interplanetary debris and dust affecting the formation of cloud layers reflecting sunlight away from the earth.
Of the two quatities, solar irradiation and albedo the Earth, by far parameter with the greates potential for variation and impact on the earth's temperature is that of the Earth's albedo, a measure of how much sunlight is reflected away from the earth.
"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."
In other words,
we know that there is alot more that we do not know,
we have neither the tools or the science to know everything we need to know,
so we will build speculative models
based only on the limited knowledge we have,
knowing that what we know is less than everything we need to know and
then we will give pretense to the public that they should make major economic-impacting public policy based on our admitted ignorance.
arrrggggggg
Lord Nelson got seasick too.
BS. The sun is a contained nuclear reaction where the container is the gravitational field of the sun itself. The gravitation field of the sun's core creates the pressure that causes the nuclear fusion which is the source of the sun's energy. The heat of the reaction causes the mantle to expand. As the mantle expands it reduces the density of the core, reducing the gravitational field and the pressure at the core. When the density of the core falls below a certain point, the rate of nuclear fusion slows, the amount of heat generated diminishes and the mantle cools and contracts increasing the core density, increasing the rate of fusion starting the cycle over again.
This cycle was part of basic physics back farther than I can remember and I have not seen anything to contradict it to date. The output of the sun is not fixed. It varies according to a natural cycle due to the forces which are the basic physics upon which the sun relies.
As I read it, changes in sunspot numbers are the main cause of variations in solar brightness. Do you have a different interpretation?
That 0.2% has a significant affect on Earth's radiative balance.
Which is one reason that cloud feedback effects are still the source of greatest uncertainty in climate models.
(Wow, a reasonable exchange. How quaint.)
Brightness of the source is not the same as incident energy flux .... not in a system like this.
Yet this warming trend has not yet reached the levels of the early Medieval Period from the 5th to 12th Centuries, when Palm trees grew in Southern England, and Greenland supported wheat cultivation. Other than a solar cause for this period of warming, what man-made global warming theory explains this?
This article simply documents a dying hoax, and the partisans struggling to keep their plans and desires for remaking the world in their ecological image alive. This hoax is dying from the shear weight of facts and common sense that exposes the flimsy nature of the rationale for today's "Global Warming Political Initiative", i.e. the unmaking of Western Industrial Capitalism in the name of Ecological Disaster Theory, which is "Global Warming". Al Gore as its "President" wishes to preside over a new paradigm in governance and social-economic planning, with the ascendancy of Eco-Technocracy to authoritarian control of our lives. Thank you Global Warming Theorists.
Second, it isn't clear from the article how they modelled the effect of increased solar radiation on the Earth's temperature. If all they're doing is adding the energy to the atmosphere's heat budget and asking what the temperature is, they're almost certainly wrong.
But the Sun is not constant. It is a varable star that grows and dims. I seem to recall that the cycle was about 9 days, but, I can't remember where I read it, maybe in Sky And Telescope. All I can remember is that they messured the brightness of Jupiter over a period of months and noted that there was a definate change in Jupiter's brightness.
Then, of course, there is the 11 year cycle, the 22 year cycle and some other 'harmonic' cycles.
Which is one reason that cloud feedback effects are still the source of greatest uncertainty in climate models.
Especially since there are so many factors affecting albedo other than the just minor direct radiation effects of atmospheric CO2 concentration that come into play that are inadequately characterized and in many cases totally lacking in the UN/IPCC climate models.
changes in sunspot numbers are the main cause of variations in solar brightness. Do you have a different interpretation?
Certainly as variations in sunspot numbers are a direct measure of the activity solar magnetic field flux being caused by said flux which varies cosmic ray incidence on the earth affecting cloud formation in much the same way as is observable in a Cloud Chamber.
Cloud density affecting Earth's albedo is a much more variable and more significant parameter than direct solar irradience any day.
Are you saying that a 150-watt bulb does not produce more heat than a 25-watt bulb?
That's really, really easy to disprove, IMHO.
Amazing that this little ball has lasted these billions of years if it is so precarisuly "balanced" that a 0.2% change in one varible makes such a big difference.
(But then again, a 350% greater change in another varible does not seem make any difference according to the "experts") < /s >
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