The Astronomical Society of Edinburgh
No 51 - December 2006
Solar global warming
In his book Gaia - A New Look at Life on Earth, James Lovelock observed that, over the last 3.5 billion years, the Sun's output has increased by 25 per cent (1). Despite this, Earth has maintained a fairly constant temperature of between 10 to 20 °C. It is surprising facts like this that underpin his Gaia hypothesis - somehow the Gaia system has managed to counteract increasing heat from the Sun.
Lovelock told me that few astronomers writing about stellar evolution consider the dull middle ages of stars. Consequently, few mention this solar warming. An exception was Nigel Henbest, who observed that 'the Sun is gradually brightening, and is now shining about half as brightly again as it was in the early history of the solar system'. He also noted that, despite this, Earth's average temperature has remained 'between the boiling point and freezing point of water'. His explanation for this was that the amount of CO2 in the atmosphere has 'depleted' (2). Henbest was writing about the time of the publication of Lovelock's Gaia book, and so probably did not realize that he was describing a Gaia activity.
But why is the Sun getting hotter? Lovelock told me that it was because, like the Earth, the Sun suffers its own global warming from a greenhouse gas. As hydrogen is fused in the core of the Sun, helium is produced. While most of this helium accumulates at the centre of the Sun, some escapes to act like a blanket and causes the core region to get hotter, so increasing the rate of the fusion reaction. However, according to Kasting, the accumulation of helium at the core causes the latter to contract and heat up, thereby making the nuclear fusion reactions proceed faster (3).
The gradual increase in the Sun's luminosity (S) is usually calculated from Gough's formula:
S = S0 / [1 + 0.4 t/t0]
Where S0 = present luminosity; t0 = 4.6; and t = time in billion years before present (4). The result is as shown in the table, where the present S is taken as 1.000.
This shows that solar luminosity has increased by 40 per cent since the Earth formed and by 30 per cent since the beginning of life (~3.5 billion years BP). The data also show that the rate of solar warming has been increasing by about 3.7 per cent per half-billion years.
The fact that the Sun was fainter in the distant past led to what is called 'The faint young Sun problem/paradox', the problem being to explain how, with a faint Sun, the Archean climates of Earth and Mars were so mild, or even warmer than today. The answer appears to be that a higher concentration of greenhouse gases (carbon dioxide and methane) was responsible. Subsequently, with the rise of oxygen about 2.3 billion years ago, a decrease in these greenhouse gases led to the paleoproterozoic glaciations, including 'Snowball Earth', when almost the whole planet was a sheet of ice. Glaciation increases Earth's albedo, reflecting more heat back into space. It also lowers sea level, so providing more land area for plants, which can absorb more CO2.
According to Lovelock, the Sun's heat was ideal for life about 2 billion years ago. Since then, although it has become progressively too hot, Earth has maintained an equable climate. Because plants produced the oxygen that led to glaciation, it can be argued that this was Gaia at work. However it seems to have overdone the cooling, nearly extinguishing all life in a planetary glaciation.
Does this mean that the present warming of Earth is partly due to solar warming? Anthropogenic warming is only about a century old, over which time the increase in solar luminosity has been only about 0.000008 per cent. Nevertheless variation in the Earth's orbit and perhaps minor changes in the solar output, on a shorter timescale than the gradual warming, may be partly responsible.
It does mean that we are frustrating Gaia's attempt to cool the planet in the face of increasing insolation. Left alone, Gaia was probably determined to bring about increased glaciation. Whatever we do about global warming, we should take note that the Sun is going to continue increasing its output. In an earlier article (5), I explained how a solar shield is one of the few ways available to cool the planet. Such a shield will be needed eventually to counter the Sun's own global warming. Left alone, Gaia would eventually have to shift to a hotter world.
Notes and references:
I refer to the OUP ed. of 2000, but it was first published in 1979. Unfortunately, Lovelock went on to claim that the Sun's output was 30 % less 3.5 billion years ago. When I pointed out this error (it was 20 % less), he was gracious enough to acknowledge his mistake and told me that I was the first person to spot the mistake in the 27 years since first publication. I noticed similar errors in his latest book (The Revenge of Gaia). When I pointed them out, he was amazed and explained that 'six otherwise good scientists have already reviewed the book without noticing these errors'. I have since pointed the need for further corrections on the matter of the relative strength of the Sun's output.
The Exploding Universe, 1979
James F. Kasting (2005): 'Methane and climate during the Precambrian era', Precambrian Research, 137, 119-129
D.O. Gough (1981): 'Solar interior structure and luminosity variations', Solar Physics, 74, 21-34
Steuart Campbell (2005): 'Cooling the Earth', ASE Journal, 48, 3-6
From: "Jeff Berkowitz (jjb)"
Date: Wed, 07 Jun 95 09:19:00 PDT
Summary: CO2 good, O2 bad
X-Moderator-Note: reprinted with permission
The Consequences of Gaia
- or -
The Carbonist Manifesto
Copyright (C) 1992 Jeff Berkowitz (firstname.lastname@example.org)
Revision 1 of 30 Nov 92
Permission to redistribute this work is granted
provided that (1) it's unmodified, (2) it's all
there ("in entirety"), and (3) my name and the
copyright notice are still attached. The fact
that Sequent's name appears in my e-mail address
has no more significance than if I gave you my
work phone number; it's just a way to reach me,
not an endorsement.
This essay describes some philosophical, ethical, and cosmological
implications of the Gaia hypothesis. Although loosely grounded in
recent research in ecology and paleoclimatology, this is clearly an
essay and not a scientific paper. It is also distinctly tongue in
cheek, but the author has spent some serious moments wondering
whether the belief system outlined below is any more unreasonable
than certain "mainstream" viewpoints.
* * * *
Over the last few years, we've become familiar with the notion that
the biosphere is a dynamic, self-regulating system. In fact, an even
stronger assertion can be made: the biosphere, in its present oxygen-
rich form, is "a kind of superorganism that in its entirety maintains
the conditions that best suit life on earth."  This formulation,
known as the Gaia Hypothesis, was originally advanced by naturalists
James Lovelock and Lynn Margulis (novelist William Golding suggested
A key point in the Gaia hypothesis concerns the stability of the
carbon cycle: that the level of atmospheric CO2 has been maintained
within relatively narrow limits for hundreds of millions of years.
This point is critical because the temperature of the biosphere
is largely controlled by the quantities of greenhouse gases
(primarily CO2) in the atmosphere. Various geophysical and
biological processes cooperate to lower the amount of free CO2
when the biosphere warms, and release CO2 when it cools. Thus
the assertion that CO2 has remained relatively constant is also
an assertion that the temperature has remained within relatively
narrow limits: at no time in the last billion years has the Earth
been a pressure cooker like Venus, or a snowball like Mars.
This essay contends that over geological time periods (in particular,
over the last 500 million years) the amount of available carbon in the
biospheric carbon cycle has slowly decreased. This decrease has been
driven by long term processes that remove CO2 from the atmosphere and
deposit it in rocks. Plants, for example, capture free carbon in the
molecules making up their tissues. As the plants die, their carbon
sometimes leaves the dynamic biological domain of the "carbon cycle"
and enters the geophysical domain as "hydrocarbon deposits" (coal,
oil, and seafloor sediments.)
Various pieces of indirect evidence exist for this slow decline in the
CO2 content of the atmosphere. Numerous plant species, for example,
thrive when subjected to an atmosphere lower in oxygen and higher in
CO2 than the current atmosphere of Earth. It is natural to suppose
that this beneficial effect is a holdover from the bygone era in which
the photosynthetic "apparatus" of these plants evolved; their initial
evolutionary "best fit" has slowly become a "misfit" due to decreasing
levels of atmospheric CO2 across intervening megalenia. Some direct
evidence of CO2 decrease also exists in the form of ice cores [1, p 42]
although it covers a much shorter time scale.
It is true that several arguments for the "essential stability" of the
atmospheric CO2 level exist, in addition to well-understood mechanisms
that "reverse the process" by removing carbon from the geophysical
domain and returning it to the biosphere (that is, the domains are not
truly separate.) It has been widely observed in the literature that
CO2 levels could never have _fallen_ to less than one-third of their
current value, nor could O2 levels have _risen_ significantly from
their current values, without deadly consequences for life .
The author finds these arguments too weak to deflect the main thrust
of this essay. None of the data presented in Garrels et al  appear
to rule out the possibility of somewhat higher atmospheric CO2 in ages
past. In fact, their discussion of the carbon cycle gives short shrift
to "reservior five" - organic carbon locked up in sediment. It is the
relationship between humankind and this crucial reservior five that we
will now continue to explore.
As we've shown, conventional reasoning links the general stability of
the carbon cycle to the general stability of biospheric temperature.
This same reasoning also serves to link the slow decrease in CO2 to an
equally slow (yet systematic) cooling of the biosphere. The Gaian
temperature "equilibrium" is not, in fact, stable. Across geological
eons, the Gaian feedback system achieves not stability, but rather a
slow cooling. Various evidence for this cooling trend exists .
Of course, the Gaian system is quite robust - as evidenced by its
repeated recovery from the effects of barrages of big rocks from
outer space. As Gaia ages, however, it is faced with the threat
of a calamity worse than the impact of a dinosaur killer. This is
the threat of "cold equilibrium", more colorfully called "the White
The White Earth scenario is part of the dirty laundry of the climate
modelling community. As noted in Gleick's "Chaos: Making a New
Science" , some seemingly reasonable (although simple) climate
models suffer from an odd characteristic of falling into a state in
which much of Gaia's free water is locked up in snow and ice; the
surface albedo of the planet is high; and no obvious mechanism for
increasing atmospheric greenhouse gas content or otherwise warming
the planet presents itself. Since this state does not seem to
correspond to anything in the historical record of the Earth, it
is regarded as anomalous and incorrect.
I suggest that we take take a truly novel approach to these seemingly
valid models that drop into the White Earth state: let's presume that
they are valid, and that they are telling us something important. We
are at risk of "cold equilibrium" in the near geological term.
The ability of the paleoclimatological community to accumulate the
data leading to this conclusion and then avoid the conclusion itself
is quite astonishing. One paleoclimatologist  has the audacity to
draw a graph of Gaian temperature that trends smoothly downward for
many millions of years, but is suddenly consumed by a series of sharp
vertical excursions ("wiggles") over the past few hundred thousand.
It's similar to the graph of a coin which rolls slowly around in a
large circle, then rattles rapidly around in an oscillating spiral
for a few moments before coming to rest in an equilibrium state,
stable and dead - Gaia converges on the White Earth.
Now let's take a step back from this impending frozen death for a
moment. The key to the Gaian system is that it is *self-adjusting*.
As observers who have only recently had our eyes opened to this
wonderful concept, the Gaian model, we cannot hope to appreciate
the myriad ways this all-encompassing system might find to regulate
itself - to adapt to conditions and to maintain the equilibrium
necessary for life. We must not underestimate the ability of the
Gaian organism to evolve temporary organelles designed to deal
The last 100,000 years have seen some of the coldest times in the
500 million that have elapsed since the Ordovician period. These
100,000 years form less than 1/1000th of the intervening 500 million
Oddly, they're the same 100,000 years that Homo Sapiens Sapiens has
existed on Earth.
Clearly, the biosphere has reached a point of crisis. The relatively
stable processes of self-regulation that have worked for the past
hundreds of millions of years have reached the limit of their ability
In response to the impending crisis, Gaia evolved a solution. At the
edges of the ice sheets that flowed down over the northern hemisphere
during the last ice age, Gaia brought it to fruition: a short term
corrective process designed to restore the natural balance of free
carbon dioxide in the biosphere.
Yes, Man. Not the destroyer, the pillager, the environmental
rapist of the popular lore; an utterly different view of Man the
restorer, the savior, the solution to an environmental crisis more
dangerous to the biosphere than even the giant stone that ended the
age of dinosaurs. Man, whose only purpose in the Gaian system is
to extract carbon from the rocks and put it back in the atmosphere
where it belongs.
It is not far-fetched to suggest that the evolution of mankind is
an adaptive reaction. Organisms under stress are known to exhibit
all manner of extraordinary behaviors. It is likely that
Levenson's "one last coincidence" [1, p 56] is not a coincidence
at all -
From 1500 to 1850, throughout the Little Ice Age, the
nations of Europe expanded in population, power, techno-
logical competence, military strength, economic endeavors,
in world rule - in virtually every measure of the vigor
of a civilization.
No, it is not a coincidence at all. It is, quite literally, our
destiny; that is why we are so well equipped to succeed and expand
our CO2-returning practices during periods of intense cold.
The climatological community has come close to the point:
Within a few centuries, we [human beings] are returning
to the atmosphere and oceans the concentrated organic
carbon stored in the sedimentary rocks over hundreds of
millions of years .
But as scientists, the community lacked the zeal to make that
final, fundamental leap from observation to motive - the observation
that this is not merely an unanticipated side effect of intelligence,
but the very reason for its existence.
Post-Gaian Environmental Ethics
Given this recognition of mankind's role in the Gaian system, it
is possible to construct a consistent system of environmental ethics
that might be called "Carbonism."
- Carbonists hold viewpoints that differ significantly from widely
accepted environmental viewpoints, but Carbonists are not wanton
destroyers of the environment. Carbonists do not favor poisoning
the environment with long-lived toxins such as heavy metals or
radioactive nucleotides, the accumulation of solid waste, or any
other practice that does not contribute the the increase of CO2
in the biosphere.
Carbonists do hold, however, that other concerns are outweighed
by the prospect of even a small increase in the necessary CO2 in
Gaia's thinning veil.
- Anything that has the direct effect of taking carbon from the
geophysical reservior and returning it to the atmosphere is good.
- Burning coal and oil for heating or to produce electric power
are the greatest goods. Temporary particulate pollution of the
atmosphere associated with these practices are of no consequence.
- Automobiles are very good. Automobiles contribute other
greenhouse gases, in addition to CO2, all at a minimal cost
in annoying particulate pollution.
- Burning wood is good. Logging is good. Slash-and-burn
agriculture is good, particularly when it is done to raise
ruminants (cud-chewing animals) which themselves contribute
nontrivial quantities of greenhouse gases to the atmosphere.
- Eating red meat is good. Consumption of red meat has an amazing
ability to act as an economic incentive for slash-and-burn
agriculture and the cultivation of ruminants in the tropical
regions of the world.
- Hydroelectric and Nuclear power are bad. They replace beneficial
coal and oil burning. Dams are also harmful to fish, and harming
fish has no evident CO2 benefit - Again, Carbonists are not wanton
destroyers of the environment.
Aside from its unfortunate tendency to substitute for coal and oil
burning, nuclear power is fairly neutral. This reflects my personal
viewpoint that the nuclear economy is unlikely to result in
significantly poisoning the environment over time. Being anti-
nuclear is the appropriate Carbonist viewpoint no matter what your
feelings about the safety of nuclear power. Nuclear safety is a
non-issue for Carbonists.
- Natural gas is not good, although it is not as bad as hydroelectric
power (it does add small amounts of certain greenhouse gases to the
atmosphere.) In most cases, however, natural gas substitutes for
the significantly more beneficial practices of burning coal or oil,
and so should be avoided.
- Air pollution is good, particularly when it kills large areas
of forest (Central Europe, California, etc.) These dead trees
are far more likely to end up rotting and burning (and hence
contributing to atmospheric CO2) than to end up in the ground.
The Longer Term and the Meaning of Life
A short term consequence of the restoration of a proper CO2 balance
to the atmosphere will be a radical drop in the number of species
within the Gaian system. This holocaust will be caused by the
inability of most species to adapt to the rapid shift in climate,
non-CO2 pollution occurring as a side effect of CO2 boosting, and
The loss of speciation might well approach the worst of the dinosaur
killer episodes in scope - perhaps 75% or more of Gaia's individual
species will disappear in a period of only a few centuries.
In the longer term, what of it? It's happened before, and it will
happen again. The Gaian system has a proven ability to recover
from loss of speciation. The destruction of 75% of Gaia's species
is a routine event of no consequence; the impending White Earth
Catastrophy offers the prospect of the death of Gaia itself - a
multibillion-year-old organism of unimaginable richness and variety.
Finally, it is worth noting that Carbonism speaks directly to the
fundamental questions of human existence in a way that is both simple
and profound. Carbonism holds that neither individual human life
nor any achievement of humanity, other than the liberation of free
carbon, has any significance whatsoever. Only the collective
behavior of the human species is significant to Gaia, and in a
few centuries (when the carbon balance has been restored) Gaia's
need for humanity will be at an end.
Mark Sweiger (email@example.com) suggested the name "Carbonism."
Reviewers of the document and victims of my lunchtime rants have
included my wife Sylvia and numerous long-suffering engineers
 Levenson, T. "Ice Time: Climate, Science, and Life on Earth."
Harper and Row, 1989, p 10 and others.
 Garrels, Lerman, Mackenzie, "Controls of Atmospheric O2 and CO2
Past, Present, and Future." In "Climates Past and Present",
Skinner, B Ed. William Kaufman Inc, 1981.
 Baes, Goeller, Olson, Rotty, "Carbon Dioxide and Climate: The
Uncontrolled Experiment." In "Climates Past and Present",
Skinner, B ed. William Kaufman Inc, 1981.
 Butzer, K. "Environment and Archeology. An Ecological Approach
to Prehistory", Second Edition. Aldine Athertone 1971, p 18.
 Hecht, A. "Paleoclimate Analysis and Modelling" John Wiley &
Sons, 1985, p 402.
 Gleick, "Chaos: Making a New Science", p 170. I've also
exchanged some email with members of the community, one of
whom indicated that explaining why this has never really
happened on earth had "the status of a cottage industry"
for a time.
Do not remove the checksum endmarker that follows.