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4 Temperature does correlate with solar activity
Correlation does not imply causation. But it does waggle its eyebrows suggestively
and gesture furtively while mouthing, ‘look over there.’[1]
Solar activity cycles have a
relatively consistent duration, lasting, on average, roughly 11 years. This can be seen in figure 11, which is
NASA’s chart of the last four centuries of solar activity. Solar cycle 23, which began in May 1996, is
winding down, but has not yet reached its end.
The incoming cycle – Solar cycle 24 – is late, and appears likely to be
unusually weak when it eventually does arrive.
Based on sunspot numbers and the length of time since the previous cycle
peaked, the coming cycle may be as low as those which preceded the Maunder
Minimum in the depths of the Little Ice Age.[2] As the Tuchman quote heading chapter 2
suggests, this was not a pleasant period for humanity. Harvests were poor, crop failures rampant,
disease persistent, and winters long and hard.
If the Earth were to return to such a climate as a result of a less active
Sun, the question of which phenomenon – solar activity or carbon dioxide – is
the key driver of terrestrial climate would be definitively answered; but the
cost for humanity could be severe.
In its Second (1996) and Third (2001) Assessment Reports,
the IPCC considered the role of solar variability in influencing climate, but
concluded that its impact was less than that of GHG forcing. On the basis of this argument, the IPCC
discounted any possible impact of solar variability
on Earth’s climate, and, in particular, on the warming that has been taking
place since the end of the Little Ice Age.[4] Indeed, in its Fourth Assessment Report
(2007), the IPCC went so far as to conclude that “during the past 50 years, the sum of solar and volcanic forcings would likely
have produced cooling.”[5] They reached this dubious conclusion despite
the fact that, during the period in question, the sun was in the midst of an
80+ year Solar Grand Maximum.[6]
Figure 11
portrays how high solar activity has been over the past half-century, compared
to the previous four hundred years. The
periodicity of solar activity cycles correlates closely with the observed
cyclical nature of global temperature.
Robinson et al., for example, make this very clear, while also
emphasizing (as noted in the last chapter) that temperatures do not correlate
at all with hydrocarbon use (see figure 12).
Apart from
the obvious impact on climate of increased or decreased solar activity (i.e.
more, or less, solar energy striking the Earth) the difficulty with the thesis
that solar activity drives atmospheric temperatures was that no one had ever
demonstrated experimentally a mechanism whereby this might be
accomplished. That changed with the
publication in 2006 of the results of a series of experiments at the Danish
National Space Centre by physicist Henrik Svensmark and his team. Noting that colder climatic periods tended to
correspond with low sunspot numbers (an indicator of solar activity, and the
key observational metric employed in measuring solar activity cycles) Svensmark
suggested that the Sun likely controlled temperatures by interfering, or not
interfering, with cosmic rays (figure 13).
Geological
evidence of periods of higher and lower cosmic ray bombardment – for example,
the presence or absence of the beryllium-10 isotope in rocks picked up by
icebergs and dropped on the ocean floor (sometimes as far south as Africa) –
suggested prima facie that periods of
intense cosmic radiation corresponded with periods of intense cold (see figure
14).
(Svensmark notes: “The upper panel shows
observations of temperatures (blue) and cosmic rays (red). The lower panel
shows the match achieved by removing El Niño, the North Atlantic Oscillation,
volcanic aerosols, and also a linear trend (0.14 § 0.4 K/Decade)”.)
|
The
mechanism that Svensmark proposed was relatively straightforward. Heavy cosmic rays – muons[9]
– are a key factor in the nucleation of low clouds because they are more likely
to penetrate further into the atmosphere.
During periods of intense solar activity, the solar wind pushes these
particles away from Earth, inhibiting low cloud formation, leading to lower
terrestrial albedo (reflectivity) and, therefore, greater warming. During periods of low solar activity,
however, the solar wind is less intense, meaning that more cosmic rays impact
the atmosphere, leading to higher rates of low cloud formation, resulting in a
higher albedo, and therefore a cooler planet.[10]
Svensmark
and his team tested this idea in 2005 and obtained experimental results
corroborating their hypothesis. Their
work has since been buttressed by proposals offered by other elements of the
space sciences, including – but not limited to – a significant correlation
between prehistoric cooling periods and the passage of the Solar System through
the spiral arms of the Milky Way Galaxy. According to a theory posited by Nir
Shaviv, an astrophysicist at the Racah Institute of Physics in Jerusalem, the
four major coolings that occurred during the half-billion-year span of animal
life on Earth can be explained by the passage of the Solar System through the
galactic arms on its quarter-billion-year gavotte around the galaxy’s core.[11]
Figure 14 - Periods of high cosmic radiation
correlate strongly with periods of heavy iceberg activity in the Atlantic Ocean
over the past 12,000 years[12]
(The empty solar
disk denotes high levels of solar activity; the darker the disk, the lower
the solar activity level. Note the
clear correlation between low solar activity, high levels of cosmic
radiation, and high levels of iceberg activity in the Atlantic Ocean.)
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The cycle
of passage through the spiral arms – which occurs roughly every 142 million
years – may be complicated by the Solar system’s oscillation above and below
the galactic plane, which further alters the exposure of the Earth to varying
intensities of cosmic radiation.[13]
Svensmark
summarizes the evidence for the link between cosmic radiation and temperature
thusly:
·
“four peaks and troughs in temperature in the
past 500 million years are matched to variations in cosmic rays as observed in
iron meteorites, and to the Solar System’s path through the galaxy;
·
“Rhythmic variations in climate over thousands
of years match the variations in production of radiocarbon and other
radionuclides by cosmic rays;
·
“Variations in the rate of warming during the
past 100 years also match the variations in cosmic-ray intensity;” and, perhaps
most importantly,
·
“The mechanism of cosmic-ray action is verified
by observations of low cloud cover correlated with cosmic-ray variations, and
by experimental evidence for the microphysical
mechanism whereby cosmic rays accelerate the production of cloud
condensation nuclei.”[14]
None of
these factors – which appear to have a far greater correlation with, and
therefore a far more significant influence on, average global temperatures than
CO2 concentration[15]
– is taken into consideration in the general circulation models (GCMs) relied
on by the proponents of the AGW thesis.
Nor, for that matter, do the GCMs pay adequate heed to the impact on
climate of fluctuations in total solar irradiance (TSI); one recent study noted
that there was a “significant TSI increase” between 1980 and 2000 and that this “could have
contributed significantly to global warming during the last three decades.” However, the authors note, the current
suite of climate models used by the IPCC assume “that the TSI did not vary significantly during the
last 30 years and have therefore underestimated the solar contribution and
overestimated the anthropogenic contribution to global warming.”[16]
That there
appears to be a correlation between solar activity and global climate should
not come as a surprise. Proponents of
the AGW thesis are fond of pointing out that without GHG like water vapour,
methane and carbon dioxide in the atmosphere, Earth’s temperature would be far
lower. It is generally agreed that, were
the Sun not present, temperatures would be somewhat lower still. As noted in the citation heading this
chapter, correlation does not by itself prove causation, but it does imply a
potential connection between phenomena that merits closer investigation in
order to determine, via experimentation, whether a causal relationship exists. This is precisely what Svensmark did with the
SKY experiment, obtaining results that corroborated his cosmic-ray nucleation
thesis. No similar experimental
corroboration has ever been obtained for the climate-forcing mechanisms
postulated in the AGW thesis.
In support of Svensmark’s thesis, Shaviv has calculated that “the total [solar]
flux entering the oceans in response to the solar cycle is about an order of
magnitude larger than the globally averaged irradiance variations of 0.17 W/m2.” He goes on to argue that that “[t]he sheer
size of the heat flux, and the lack of any phase lag between the flux and the
driving force further implies that it cannot be part of an atmospheric feedback
and [is] very unlikely to be part of a coupled atmosphere-ocean oscillation
mode”; and concludes that oceanic warming correlating with solar activity
levels “must therefore be the manifestation of real variations in the global radiative
forcing.”[17]
Shaviv
stresses that
the observed correlation between the oceanic heat flux
and solar activity does not provide proof for any particular amplification
mechanism, including that of the CRF [cosmic ray flux]/climate link. It does
however provide very strong support for the notion that an amplification mechanism
exists. Given that the CRF/climate links predicts the correct radiation
imbalance observed in the cloud cover variations, it is a favorable candidate.[18]
We are, as
noted above, coming to the end of a Solar Grand Maximum, during which the Sun
was more active, and for longer periods, than at any time in the past 11,000
years.[19] If the Svensmark thesis is correct, we should
not be surprised that this period of heightened solar activity corresponds with
the slight warming observed over the past three centuries as the Earth
recovered from the Little Ice Age. It should
also not be surprising that similar surface warming has been observed on Mars,[20]
Jupiter,[21]
Triton (Neptune’s largest moon),[22]
and even Pluto.[23] Scientists who dispute the thesis that solar
activity may be the principal cause of warming on Mars and the outer planets
tend to base their arguments on the fact that the delta in direct heating due
to fluctuations in total solar irradiance appears to be too low to directly
warm these planets. However, if Svensmark’s
thesis, and Shaviv’s calculations, are correct, then the amplifying effect of
changes in the cosmic ray flux attributable to fluctuations in solar activity could
account for observed extra-terrestrial warming.
Logically,
when seeking the source of simultaneous warming on five different planets, one
would look for an agent capable of affecting them all simultaneously. It certainly cannot have been human activity;
there has, after all, been very little human activity on Mars, Jupiter, Triton
or Pluto, none of it involving the consumption of fossil fuels. The obvious candidate, faute de mieux, is the Sun.
Svensmark has demonstrated a mechanism whereby solar activity can directly
influence planetary climates, and his proposal has been verified both theoretically
and experimentally. Why has this
discovery, and its obvious significance for climate science, not been
acknowledged (much less explained) by the AGW theorists?
To focus
on a non-correlating phenomenon while studiously ignoring other phenomena that
correlate closely with observed, historical and proxy temperature records, and that
therefore offer far greater explicatory power, is thoroughly unscientific. This is not merely a question of choosing, in
obedience to Occam’s Razor, the less complex of two equally valid
hypotheses. It is a question of choosing
between one hypothesis that offers a credible explanation for observed data,
and another that does not.
[1]
Randall Munroe, physicist, [http://xkcd.com/552/].
[2]
Svensmark and Calder, 225.
[3]
NASA.gov, 7 November 2008 [http://science.nasa.gov/headlines/y2008/11jul_solarcycleupdate.htm].
[4] In the TAR, the IPCC acknowledged that “studies include uncertainties in forcing due to
anthropogenic sulfate aerosols and natural factors (volcanoes and solar
irradiance)” but argued that “natural forcings are negative over this period and cannot explain the warming”. IPCC, “Climate Change 2001: Synthesis Report
– Summary for Policymakers”, 5.
[5]
IPCC, “Climate Change 2007: Synthesis Report – Summary for Policymakers”, 5. Emphasis added.
[6]
“Recent activity has been abnormally high for at least 8 cycles.” J.A. Abreu, et al., “For how long will the
current grand maximum of solar activity persist?”, Geophysical Research Letters, Volume 35, Issue 20, October 2008.
[7]
Robinson, Robinson & Soon,
79.
[8] Henrik
Svensmark and Eigil Friis-Christensen, “Reply to Lockwood and Fröhlich -
The persistent role of the Sun in climate forcing”,
Danish National Space Centre, Scientific Report 3/2007, ISBN-10 87-91694-14-0,
1.
[9]
A muon is a negatively-charged particle with 200 times the mass of an
electron. They are also very unstable,
surviving only for two-millionths of a second before shedding two neutrinos to
become a normal electron.
[10] For a complete overview of the cosmic-ray nucleation
thesis and the results of the SKY experiment, see Henrik Svensmark and Nigel
Calder, The Chilling Stars: A Cosmic View
of Climate Change (Cambridge, UK: Icon Books, 2007). See also N.D. Marsh and H. Svensmark, “Low cloud properties influenced by cosmic rays”, Physical
Review Letters 85 (2000), p. 5004-5007.
[11] See N. Shaviv and J. Veizer, “Celestial driver of phanerozoic climate?”, Geological Society of
America 13 (2003), 4-10.
[12]
Svensmark and Calder, The Chilling Stars, 25.
[13] Svensmark and Calder, The Chilling Stars, 132-55.
See also R.G. Harrison and D.B.Stephenson, “Empirical evidence for a
nonlinear effect of galactic cosmic rays on clouds” Proceedings
of the Royal Society A (UK): 10.1098 / rspa.2005.1628 (2006).
[14]
Svensmark and Calder, 248.
[15] Tree ring proxy studies show a high correlation
(R=0.58-0.94) with solar periodicity, especially the 200-year de Vries
cycle. O.M. Raspopov, et al., “The influence of the de Vries (~200-year) solar
cycle on climate variations: Results from the Central Asian Mountains and their global link”, Palaeogeography, Palaeoclimatology, Palaeoecology 259
(2008), 15.
[16]
N. Scafetta and R. C. Willson “ACRIM-gap and TSI trend issue resolved using a
surface magnetic flux TSI proxy model”, Geophysical
Research Letters 36 (2009)
L05701, doi:10.1029/2008GL036307 [http://www.agu.org/pubs/crossref/2009/2008GL036307.shtml].
[17]
Some climate scientists, e.g.,
Joseph D’Aleo, have made persuasive arguments that oceanic cycles (for example,
the Pacific Decadal Oscillation, or PDO) can have a strong forcing effect on
climate. In a presentation to a recent
scientific conference on climate change, D’Aleo demonstrated a statistically
significant synchrony between US annual temperatures, oceanic cycles and Total
Solar Irradiance (this should not surprise us, as water covers 70% of our
planet, and thus intercepts 70% of the solar energy striking the planet). D’Aleo noted that the trend-lines for both
the PDO and TSI at present indicate imminent cooling. D’Aleo’s presentation may be found at [http://www.heartland.org/events/NewYork09/
proceedings.html].
[18]
Nir Shaviv,
“Using the oceans as a calorimeter to quantify the solar radiative forcing”, Journal of
Geophysical Research 113 (2008), A11101,
doi:10.1029/2007JA012989, paras 73-74 [http://www.friendsofscience.org/assets/documents/Oceans_Solar_Forcing.pdf].
[19] See Zbigniew Jaworowski, “CO2:
The Greatest Scientific Scandal Of Our Time”, 21st Century Science and Technology, Spring/Summer 2007,
22. In 2008, Jaworowski was chairman of the Scientific Council of
the Central Laboratory for Radiological Protection in Warsaw, and is the former
chair of the United Nations Scientific Committee on the Effects of Atomic
Radiation.
[20]
This argument has been brought forward by many astrophysicists, including
Michael Malin of the Mars Orbiter programme at NASA (“…for three Mars summers
in a row, deposits of frozen carbon dioxide near Mars' south pole have shrunk
from the previous year's size, suggesting a climate change in progress.”). NASA JPL, “Orbiter’s Long Life Helps
Scientists Track Changes on Mars”, NASA Press Release, 20 September 2005 [http://mars.jpl.nasa.gov/mgs/newsroom/20050920a.html]. Warming on other planets in the Solar System
has also been noted by Habibullo Abdussamatov, head of space research at St.
Petersburg's Pulkovo Astronomical Observatory in Russia. Kate Ravilious, “Mars Melt Hints At Solar, Not
Human, Cause For Warming, Scientist Says”, National Geographic News, 28
February 2007 [http://news.nationalgeographic.com/news/2007/02/070228-mars-warming.html].
[21]
Sara Goudarzi, “New Storm on
Jupiter Hints at Climate Change”, Space.com, 4 May 2006 [http://www.space.com/scienceastronomy/060504_red_jr.html].
[22]
Massachusetts Institute of
Technology, “MIT research finds evidence of global warming on Neptune’s largest
moon”, MIT News Office, 24 June 1998, [http://web.mit.edu/newsoffice/1998/triton.html].
[23]
Massachusetts Institute of Technology, “Pluto is undergoing global warming,
researchers find”, MIT News Office, 9 October 2002 [http://web.mit.edu/newsoffice/2002/pluto.html].
It should be noted that there are other possible explanations, including
Pluto’s highly eccentric orbit, for this phenomenon. See also Lorne Gunter, “Bright Sun, Warm Earth: Coincidence?”, National Post, 12 March 2007.
