Not assumed to be caused, but known to be caused. The science is clear,
it's only that the vast majority of the population is science
illiterate to the point that many people with university degrees in
economics, engineering etc. don't know much about physics and are
susceptible to the same nonsense as most lay persons.
http://www.sciencemag.org/content/330/6002/356.full
ABSTRACT
Ample physical evidence shows that carbon dioxide (CO2) is the single
most important climate-relevant greenhouse gas in Earth¡¯s atmosphere.
This is because CO2, like ozone, N2O, CH4, and chlorofluorocarbons,
does not condense and precipitate from the atmosphere at current
climate temperatures, whereas water vapor can and does. Noncondensing
greenhouse gases, which account for 25% of the total terrestrial
greenhouse effect, thus serve to provide the stable temperature
structure that sustains the current levels of atmospheric water vapor
and clouds via feedback processes that account for the remaining 75% of
the greenhouse effect. Without the radiative forcing supplied by CO2
and the other noncondensing greenhouse gases, the terrestrial
greenhouse would collapse, plunging the global climate into an icebound
Earth state.
It often is stated that water vapor is the chief greenhouse gas (GHG)
in the atmosphere. For example, it has been asserted that ¡°about 98%
of the natural greenhouse effect is due to water vapour and stratiform
clouds with CO2 contributing less than 2%¡± (1). If true, this would
imply that changes in atmospheric CO2 are not important influences on
the natural greenhouse capacity of Earth, and that the continuing
increase in CO2 due to human activity is therefore not relevant to
climate change. This misunderstanding is resolved through simple
examination of the terrestrial greenhouse.
The difference between the nominal global mean surface temperature (TS
= 288 K) and the global mean effective temperature (TE = 255 K) is a
common measure of the terrestrial greenhouse effect (GT = TS ¨C TE = 33
K). Assuming global energy balance, TE is also the Planck radiation
equivalent of the 240 W/m2 of global mean solar radiation absorbed by
Earth.
The Sun is the source of energy that heats Earth. Besides direct solar
heating of the ground, there is also indirect longwave (LW) warming
arising from the thermal radiation that is emitted by the ground, then
absorbed locally within the atmosphere, from which it is re-emitted in
both upward and downward directions, further heating the ground and
maintaining the temperature gradient in the atmosphere. This radiative
interaction is the greenhouse effect, which was first discovered by
Joseph Fourier in 1824 (2), experimentally verified by John Tyndall in
1863 (3), and quantified by Svante Arrhenius in 1896 (4). These studies
established long ago that water vapor and CO2 are indeed the principal
terrestrial GHGs. Now, further consideration shows that CO2 is the one
that controls climate change.
CO2 is a well-mixed gas that does not condense or precipitate from the
atmosphere. Water vapor and clouds, on the other hand, are highly
active components of the climate system that respond rapidly to changes
in temperature and air pressure by evaporating, condensing, and
precipitating. This identifies water vapor and clouds as the fast
feedback processes in the climate system.
Radiative forcing experiments assuming doubled CO2 and a 2% increase in
solar irradiance (5) show that water vapor provides the strongest
climate feedback of any of the atmospheric GHGs, but that it is not the
cause (forcing) of global climate change. The response of the climate
system to an applied forcing is determined to be the sum of the direct
(no-feedback) response to the applied forcing and the induced radiative
response that is attributable to the feedback process contributions.
The ratio of the total climate response to the no-feedback response is
commonly known as the feedback factor, which incorporates all the
complexities of the climate system feedback interactions. For the
doubled CO2 and the 2% solar irradiance forcings, for which the direct
no-feedback responses of the global surface temperature are 1.2¡ã and
1.3¡ãC, respectively, the ~4¡ãC surface warming implies respective
feedback factors of 3.3 and 3.0 (5).
Because the solar-thermal energy balance of Earth [at the top of the
atmosphere (TOA)] is maintained by radiative processes only, and
because all the global net advective energy transports must equal zero,
it follows that the global average surface temperature must be
determined in full by the radiative fluxes arising from the patterns of
temperature and absorption of radiation. This then is the basic
underlying physics that explains the close coupling that exists between
TOA radiative fluxes, the greenhouse effect, and the global mean
surface temperature.
An improved understanding of the relative importance of the different
contributors to the greenhouse effect comes from radiative flux
experiments that we performed using Goddard Institute for Space Studies
(GISS) ModelE (6). Figure 1 depicts the essence of these calculations,
including the separation of the greenhouse contributors into feedback
and forcing categories.
In round numbers, water vapor accounts for about 50% of Earth¡¯s
greenhouse effect, with clouds contributing 25%, CO2 20%, and the minor
GHGs and aerosols accounting for the remaining 5%. Because CO2, O3,
N2O, CH4, and chlorofluorocarbons (CFCs) do not condense and
precipitate, noncondensing GHGs constitute the key 25% of the radiative
forcing that supports and sustains the entire terrestrial greenhouse
effect, the remaining 75% coming as fast feedback contributions from
water vapor and clouds.
We used the GISS 4¡ã ¡Á 5¡ã ModelE to calculate changes in
instantaneous LW TOA flux (annual global averages) in experiments where
atmospheric constituents (including water vapor, clouds, CO2, O3, N2O,
CH4, CFCs, and aerosols) were added to or subtracted from an
equilibrium atmosphere with a given global temperature structure, one
constituent at a time for a 1-year period. Decreases in outgoing TOA
flux for each constituent relative to the empty or the full-component
atmosphere define the bounds for the relative impact on the total
greenhouse effect. Had the overlapping absorption been negligible, the
sum of the flux differences would have been equal to the LW flux
equivalent of the total greenhouse effect (GF = ¦ÒTS^4 ¨C ¦ÒTE^4 = 150
W/m2), where ¦Ò is the Stefan-Boltzmann constant. We found the
single-addition flux differences to be overestimated by a factor of
1.36, whereas in the single-subtraction cases, the sum of the TOA flux
differences was underestimated by a factor of 0.734. By normalizing
these fractional contributions to match the full-atmosphere value of
GF, we obtained the fractional response contributions shown in Fig. 1.
Because of overlapping absorption, the fractional attribution of the
greenhouse effect is to some extent qualitative (as shown by the dashed
and dotted extremum lines in Fig. 1), even though the spectral integral
is a full and accurate determination of the atmospheric greenhouse
strength for the specified global temperature structure. Still, the
fractional attribution is sufficiently precise to clearly differentiate
the radiative flux contributions due to the noncondensable GHGs from
those arising from the fast feedback processes. This allows an
empirical determination of the climate feedback factor as the ratio of
the total global flux change to the flux change that is attributable to
the radiative forcing due to the noncondensing GHGs. This empirical
determination leads then to a climate feedback factor of 4, based on
the noncondensing GHG forcing accounting for 25% of the outgoing flux
reduction at the TOA for the full-constituent atmosphere. This implies
that Earth¡¯s climate system operates with strong positive feedback
that arises from the forcing-induced changes in the condensable species.
A direct consequence of this combination of feedback by the condensable
and forcing by the noncondensable constituents of the atmospheric
greenhouse is that the terrestrial greenhouse effect would collapse
were it not for the presence of these noncondensing GHGs. If the global
atmospheric temperatures were to fall to as low as TS = TE, the
Clausius-Clapeyron relation would imply that the sustainable amount of
atmospheric water vapor would become less than 10% of the current
atmospheric value. This would result in (radiative) forcing reduced by
~30 W/m2, causing much of the remaining water vapor to precipitate,
thus enhancing the snow/ice albedo to further diminish the absorbed
solar radiation. Such a condition would inevitably lead to runaway
glaciation, producing an ice ball Earth.
Claims that removing all CO2 from the atmosphere ¡°would lead to a 1¡ãC
decrease in global warming¡± (7), or ¡°by 3.53¡ãC when 40% cloud cover
is assumed¡± [8] are still being heard. A clear demonstration is needed
to show that water vapor and clouds do indeed behave as fast feedback
processes and that their atmospheric distributions are regulated by the
sustained radiative forcing due to the noncondensing GHGs. To this end,
we performed a simple climate experiment with the GISS 2¡ã ¡Á 2.5¡ã AR5
version of ModelE, using the Q-flux ocean with a mixed-layer depth of
250 m, zeroing out all the noncondensing GHGs and aerosols.
The results, summarized in Fig. 2, show unequivocally that the
radiative forcing by noncondensing GHGs is essential to sustain the
atmospheric temperatures that are needed for significant levels of
water vapor and cloud feedback. Without this noncondensable GHG
forcing, the physics of this model send the climate of Earth plunging
rapidly and irrevocably to an icebound state, though perhaps not to
total ocean freezeover.
The scope of the climate impact becomes apparent in just 10 years.
During the first year alone, global mean surface temperature falls by
4.6¡ãC. After 50 years, the global temperature stands at ¨C21¡ãC, a
decrease of 34.8¡ãC. Atmospheric water vapor is at ~10% of the control
climate value (22.6 to 2.2 mm). Global cloud cover increases from its
58% control value to more than 75%, and the global sea ice fraction
goes from 4.6% to 46.7%, causing the planetary albedo of Earth to also
increase from ~29% to 41.8%. This has the effect of reducing the
absorbed solar energy to further exacerbate the global cooling.
After 50 years, a third of the ocean surface still remains ice-free,
even though the global surface temperature is colder than ¨C21¡ãC. At
tropical latitudes, incident solar radiation is sufficient to keep the
ocean from freezing. Although this thermal oasis within an otherwise
icebound Earth appears to be stable, further calculations with an
interactive ocean would be needed to verify the potential for long-term
stability. The surface temperatures in Fig. 3 are only marginally
warmer than 1¡ãC within the remaining low-latitude heat island.
From the foregoing, it is clear that CO2 is the key atmospheric gas
that exerts principal control over the strength of the terrestrial
greenhouse effect. Water vapor and clouds are fast-acting feedback
effects, and as such are controlled by the radiative forcings supplied
by the noncondensing GHGs. There is telling evidence that atmospheric
CO2 also governs the temperature of Earth on geological time scales,
suggesting the related question of what the geological processes that
control atmospheric CO2 are. The geological evidence of glaciation at
tropical latitudes from 650 to 750 million years ago supports the
snowball Earth hypothesis (9), and by inference, that escape from the
snowball Earth condition is also achievable.
On million-year time scales, volcanoes are the principal source of
atmospheric CO2, and rock weathering is the principal sink, with the
biosphere acting as both source and sink (10). Because the CO2 sources
and sinks operate independently, the atmospheric level of CO2 can
fluctuate. If the atmospheric CO2 level were to fall below its critical
value, snowball Earth conditions can result.
Antarctic and Greenland ice core data show atmospheric CO2 fluctuations
between 180 to 300 parts per million (ppm) over the
glacial-interglacial cycles during the past 650,000 years (11). The
relevant physical processes that turn the CO2 control knob on
thousand-year time scales between glacial and interglacial extremes are
not fully understood, but appear to involve both the biosphere and the
ocean chemistry, including a significant role for Milankovitch
variations of the Earth-orbital parameters.
Besides CO2, methane is another potent greenhouse control knob, being
implicated in the Paleocene-Eocene thermal maximummass extinction 55
million years ago, when global warming by up to 5¡ãC (12) occurred
because of a massive release of methane from the disintegration of
seafloor clathrates (13, 14). Methane is the second most important
noncondensing GHG after CO2. Of the 2.9 W/m2 of GHG radiative forcing
from 1750 to 2000, CO2 contributed 1.5 W/m2, methane 0.55 W/m2, and
CFCs 0.3 W/m2, with the rest coming from N2O and ozone (15). All of
these increases in noncondensing GHG forcing are attributable to human
activity (16).
Climate control knobs on the solar side of the energy balance ledger
include the steady growth in luminosity since the beginning of the
Solar System (from about 70% of present luminosity, depending on the
postulated early solar mass loss), as hydrogen is consumed in nuclear
reactions in the solar interior (17, 18). Milankovitch variations of
the Earth-orbital parameters, which alter the relative seasonal
distribution as well as the intensity of incident solar radiation
within the polar regions, are another important solar energy control
knob that is intimately associated with glacial-interglacial cycles of
climate change. For solar irradiance changes over the past several
centuries, an increase by about 0.1 W/m2 is inferred since the time of
the Maunder minimum, based on trends in sunspot activity and other
proxies (19).
Of the climate control knobs relevant to current climate, those on the
solar side of the energy balance ledger show only negligible impact.
Several decades of solar irradiance monitoring have not detected any
long-term trends in solar irradiance beyond the 11-year oscillation
associated with the solar sunspot cycle. Large volcanic eruptions can
happen at any time, but no substantial eruptions have occurred since
the eruption of Mt. Pinatubo in the Philippines in 1991.
In a broader perspective, CO2 greenhouses also operate on Mars and
Venus, because both planets possess atmospheres with substantial
amounts of CO2. The atmospheric greenhouse effect requires that a
substantial fraction of the incident solar radiation must be absorbed
at the ground in order to make the indirect greenhouse heating of the
ground surface possible. Greenhouse parameters and relative surface
pressure (PS) for Mars, Earth, and Venus are summarized in Table 1.
Earth is unique among terrestrial planets in having a greenhouse effect
in which water vapor provides strong amplification of the heat-trapping
action of the CO2 greenhouse. Also, N2 and O2, although possessing no
substantial absorption bands of their own, are actually important
contributors to the total greenhouse effect because of
pressure-broadening of CO2 absorption lines, as well as by providing
the physical structure within which the absorbing gases can interact
with the radiation field.
The anthropogenic radiative forcings that fuel the growing terrestrial
greenhouse effect continue unabated. The continuing high rate of
atmospheric CO2 increase is particularly worrisome, because the present
CO2 level of 390 ppm is far in excess of the 280 ppm that is more
typical for the interglacial maximum, and still the atmospheric CO2
control knob is now being turned faster than at any time in the
geological record (20). The concern is that we are well past even the
300- to 350-ppm target level for atmospheric CO2, beyond which
dangerous anthropogenic interference in the climate system would exceed
the 25% risk tolerance for impending degradation of land and ocean
ecosystems, sea-level rise, and inevitable disruption of socioeconomic
and food-producing infrastructure (21, 22). Furthermore, the
atmospheric residence time of CO2 is exceedingly long, being measured
in thousands of years (23). This makes the reduction and control of
atmospheric CO2 a serious and pressing issue, worthy of real-time
attention.
Citeren Roger Clough <[email protected]>:
On Global Warming----The sun is getting a little hotter
Up to the present day, studies of global warming were
based on CO2 levels in the atmosphere, assumed to be caused by
automobiles (the supposed greenhouse effect).
But more resent studies show that total solar irradiation (TSI) --
solar radiation coming from outside of the atmosphere- not CO2 levels--
is the driving force:
http://wattsupwiththat.com/2012/09/06/soon-and-briggs-global-warming-fanatics-take-note-sunspots-do-impact-climate/
C02 levels are not reliable indicators of what causes surface
temperature warming (the supposed greenhouse effect) ?
.
Why ? Because some of the CO2 in the atmosphere is there because as
the earth warms, the
oceans warm and CO2 gases sare less soluble in warmer water, so fizle out
into the atmosphere. So it is doubtful to say that current levels of CO2
are entirely from automobiles.
So current scientific evalutations as in the graph below do not rely on CO2
measurements, they use solar radiation which is not influenced by C02 levels
and relate that instead to surface gtemperatures.
The total solar radiation (TSI) is not obtained from measurements
made on earth, so
it isn't supposed to include greenshouse gas effects. It is measured
these days by satellite,
but is reconconstructed from pre-satellite days (<1979 ) based on a model
based on the number of sunspots.
http://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/abs/2007/19/aa6725-06/aa6725-06.html
"Reconstruction of solar total irradiance since 1700 from the surface
magnetic flux
N. A. Krivova, L. Balmaceda, and S. K. Solanki
Max-Planck-Institut f? Sonnensystemforschung, Max-Planck-Str. 2,
37191 Katlenburg-Lindau, Germany
e-mail: [email protected]
(Received 9 November 2006 / Accepted 23 February 2007)
Abstract
Context.Total solar irradiance changes by about 0.1% between solar
activity maximum and minimum. Accurate measurements of this quantity
are only available since 1978 and do not provide information on
longer-term secular trends.
Aims.In order to reliably evaluate the Sun's role in recent global
climate change, longer time series are, however, needed. They can
only be assessed with the help of suitable models.
Methods.The total solar irradiance is reconstructed from the end of
the Maunder minimum to the present based on variations of the surface
distribution of the solar magnetic field. The latter is calculated
from the historical record of the sunspot number using a simple but
consistent physical model.
Results.Our model successfully reproduces three independent data
sets: total solar irradiance measurements available since 1978, total
photospheric magnetic flux since 1974 and the open magnetic flux
since 1868 empirically reconstructed using the geomagnetic aa-index.
The model predicts an increase in the solar total irradiance since
the Maunder minimum of $1.3^{\rm +0.2}_{\rm -0.4}$ Wm-2. "
Dr. Roger Clough NIST (ret.) 3/30/2013
"Coincidences are God's way of remaining anonymous."
- Albert Einstein
____________________________________________________________________
Dr. Roger Clough NIST (ret.) 6/15/2013
See my Leibniz site at
http://team.academia.edu/RogerClough
____________________________________________________________________
DreamMail - The first mail software supporting source tracking
www.dreammail.org
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