Today in Astronomy 106: cultural self-destruction
Self-imposed limitations on
a civilization’s lifespan:
 Uncommunicativeness
 Overpopulation and
Malthusian collapse
 Resource depletion
 Destruction of habitat:
• Nuclear war and nuclear
winter
• CO2, ocean acidification,
and catastrophic global
warming
19 November 2015
Ivy Mike: the first US H Bomb, 1
November 1952, with a yield of 10
megatons (US Department of Energy)
Astronomy 106, Fall 2015
1
The main achievements of these
two civilizations were invented
independently of one another:
:30
Astronomy 106, Fall 2015
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19 November 2015
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India and China
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A. China and Egypt
2
Shooting ourselves in the foot
Technological civilizations can collapse and/or lose the ability to
communicate with those on other planets by two general means: selfinflicted damage and natural disasters. First we shall discuss the selfinflicted sort, of which there are four main types, listed here in increasing
order of danger:
 Loss of interest in searching for other civilizations, while retaining
technological capability.
 Population growth to the point of societal collapse.
 Depletion of resources within reach of the civilization.
 Destruction of the habitability of the planet(s) on which the
civilization resides.
19 November 2015
Astronomy 106, Fall 2015
3
Being uncommunicative
Just because a civilization can communicate with others far away doesn’t
mean it will. Best local analogy: China.
 China has been a leading civilization, capable of exploring far past its
borders, continuously for about 3500 years.
 Yet for almost all of this time she has not only denied interest in other
cultures, but has been proud of that.
• e.g. the Qing dynasty’s Qianlong Emperor,
in refusing the British request to exchange
ambassadors in 1793:
This request is contrary to all usage of my
dynasty…I set no value on objects strange or
ingenious, and have no use for your country’s
manufactures.
19 November 2015
Astronomy 106, Fall 2015
4
Being uncommunicative (continued)
 In the early years of the Tang Dynasty (618-907 AD), the borders of
China were advanced along the Silk Road as far as modern
Kazakhstan, but China lost interest in further advance after losing a
battle (Talas River, 751 AD) to the Arabs of the Abbasid Caliphate,
never establishing permanent political relationships in the West.
 The third ruler of the Ming Dynasty,
the Yongle Emperor, sent his vizier
Zheng He – in a fleet of 1500-ton ships
– on seven voyages of exploration and
tribute collection (1405-1423 AD) that
made it as far as East Africa: the only
explorations in Chinese history.
So although China was capable of communication, her communicative phase was short:
L = 18 years, 0.5% of the possible lifetime.
19 November 2015
Astronomy 106, Fall 2015
Talas R.
Wikimedia Commons
5
If there are other civilizations
nearby in the Galaxy, should we try
to communicate with them?
A. True
:15
50%
50%
B. False
19 November 2015
Astronomy 106, Fall 2015
Fa
l se
Tr
ue
(i.e. yes, no)
6
Overpopulation and collapse
Thomas Malthus remarked famously (1798) that population seems
inevitably to increase faster than its means of subsistence – food – can
increase:
The power of population is so superior to the power of the earth to
produce subsistence for man, that premature death must in some
shape or other visit the human race … should [armies] fail in [their]
war of extermination, sickly seasons, epidemics, pestilence, and
plague advance in terrific array, and sweep off their thousands and
tens of thousands. Should success be still incomplete, gigantic
inevitable famine stalks in the rear, and with one mighty blow levels
the population with the food of the world.
On this basis Malthus expressed worries about the viability of several
nations, and one of his chief worries was Ireland. Soon Ireland became the
exemplar of this form of collapse.
19 November 2015
Astronomy 106, Fall 2015
7
Overpopulation and collapse (continued)
 From the early 1700s on, Ireland, with a population of 7-8 million, was
on the very edge of being able to feed itself. Ireland’s poor relied
almost exclusively on potatoes for nutrition.
 When a blight destroyed the potato crop two years in a row (1845-46),
two million died, three million emigrated, and the Irish nation was
virtually destroyed.
 Although Malthus was certainly right about Ireland, there was an
interesting additional, evolutionary, factor at play: only a few
varieties of the ~100 different strains of potatoes in the Andes had
made it to Europe.
• This left the crops vulnerable to a well-aimed disease that
wouldn’t have been a problem in a more diverse plant
population.
19 November 2015
Astronomy 106, Fall 2015
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Overpopulation and collapse (continued)
Two examples on larger scale:
 By the end of the third century
AD, both the Roman and Han
Chinese empires were populated
near the limit of their subsistence.
 Repeated epidemics, and
probably a minor cooling of
global climate, sent both empires
into tailspins from which neither
recovered; their civilizations and
influence were destroyed.
Earth can feed a maximum of about 20 billion; the current population is
over 7 billion and doubling every 55 years.
19 November 2015
Astronomy 106, Fall 2015
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Resource depletion and collapse
Resource-abuse-related micro-examples in the collapse
of civilizations on Earth (Diamond 2004):
 On Easter Island, Polynesian colonists, unused to
the timescale for tree growth in more temperate
climates, systematically deforested the island and
left themselves without transportation and fishing
vessels. Probably about 70% population loss.
 The Greenland Norse practiced forms of farming,
shipbuilding and weaponry, developed in
Scandinavia, that were unsustainable on Greenland;
unsustainability became catastrophic when they ran
out of wood and iron, ceased to be visited from
Iceland, and endured worsening climate (the Little
Ice Age) in the late 15th century.
19 November 2015
Astronomy 106, Fall 2015
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Resource depletion and collapse (continued)
Globally we are now using technology which is based upon access to
resources we are using unsustainably, mostly in the realm of
nonrenewable resources like petroleum and natural gas. Petrochemicals
provide, among other things,
 our highest-energy-density fuels, without which aviation would be
far more difficult.
 plastics, without which modern technology is scarcely imaginable.
 fertilizers, important in maintaining the high crop yields upon which
we have come to depend.
A sudden collapse, either of technology or population, may attend the
exhaustion of this resource, if we’re not careful.
19 November 2015
Astronomy 106, Fall 2015
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Resource depletion and collapse (continued)
Unsustainable?
 At the largest sober
estimate, we
currently have
approximately 104
petagrams (Pgm) of
carbon in the form
of coal, oil and
natural gas
underground.
Underground
reservoirs: limestone,
coal, oil. About 93%
of Earth’s carbon.
gm
(1 Pgm =
= 109 ton = 1 Gt)
1015
Woods Hole Research Center; see also Le Quéré et al. 2009.
19 November 2015
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Resource depletion and collapse (continued)
 We currently burn 7.7 Pgm of this per year. At this rate the fossil fuels
would last 1300 years.
 But the burn rate is increasing roughly linearly, doubling every 22
years. At this rate, 10,000 Pgm would last only 138 years.
So, yeah, we’d better save some – and not just because running out would
be a bad thing, as we shall see.
Global anthropogenic
CO2 emissions (IPCC
#5).
19 November 2015
Astronomy 106, Fall 2015
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Destruction of habitability
For sixty years, humans have held the power to destroy their habitat, by
three primary means. We’ll discuss two. (Third is pollution of air and
fresh water. )
 Weapons of mass destruction, such as nuclear weapons. From 1965 to
1985, the arsenals of the USA and USSR contained about 60,000 warheads,
totalling 40,000 megatons. Same as
 five Class 5 hurricanes, though more concentrated.
 impact of a few-km diameter asteroid.
 200 large volcanic explosions (e.g. Krakatoa 1883).
But worst of all,
 ten times as much as would completely destroy every large city in
each country.
19 November 2015
Astronomy 106, Fall 2015
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Destruction of habitability (continued)
Result of all-out nuclear war:
 Aimed preferentially at cities, so population would be preferentially
destroyed.
 H-bomb-destroyed cities would turn very efficiently into dust, which
would scatter and rise in the atmosphere.
 This in turn would prevent sunlight from reaching the ground (5090% of it), and temperatures would drop and stay low for several
years: nuclear winter.
 And this, in turn, would cause a progressive collapse of the food
chain, much as in the case of prehistoric extinctions.
 Outcome accurately portrayed in many movies.
19 November 2015
Astronomy 106, Fall 2015
15
What do you think will get us first?
Exhaustion of energy
resources.
C.
Exhaustion of other
technological necessities.
D.
Nuclear destruction.
E.
Other.
Astronomy 106, Fall 2015
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A. Overpopulation.
19 November 2015
:30
16
Mid-lecture Break
 Homework #5
is available on
WeBWorK; it’s
due next
Wednesday, 25
November 2015,
7PM.
Major T.J. “King” Kong rodeo-rides an H bomb down
to Siberia. (From Stanley Kubrick’s Dr. Strangelove,
1964)
19 November 2015
Astronomy 106, Fall 2015
17
Destruction of habitability (continued)
 Emission of carbon dioxide gas. The concentration of CO2 in the
atmosphere and the oceans is governed by the following interlocking
cycles.
 Plants. CO2 is removed from the atmosphere by photosynthesis at a
rate proportional to the number of plants.
• In turn plants return CO2 to the atmosphere as they use
photosynthetic energy (respiration).
• But not all: plants sequester carbon as they grow, and as they add
to Earth’s crust when they die – as soil, and over longer terms as
coal, oil and natural gas.
 Ocean. CO2 dissolves in water, producing carbonic acid: H2CO3, or in
solution H3O+ and HCO3-.
19 November 2015
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Destruction of habitability (continued)
 Not that readily in ocean water: only about 10% of any increase in
atmospheric CO2 gets dissolved (Revelle & Suess 1957), but enough
that the near-surface acidity of the ocean is significantly affected.
• About 40% of the CO2 added since 1750 is still in the atmosphere;
30% is dissolved in the ocean.
 Carbonic acid in rain weathers rocks, and adds calcium to the runoff.
 In the ocean, and in addition to photosynthesis, several
microorganisms sequester carbon by converting calcium and
carbonic acid into calcium carbonate (CaCO3) in shells and coral. They
also respire some CO2.
 Some of the shells and corals are subducted on ~10 My time scales
along with the rest of the ocean plates; some is included as limestone
in the continental plates.
19 November 2015
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Destruction of habitability (continued)
 Burning fossil fuels and carbonate rocks. In all, about 20% of the
carbon underground currently in the form of coal, oil and gas, and
most of the rest is in the form of limestone, which is burned to make
concrete. This sequestration of about 93% of Earth’s carbon was vital
in producing the atmospheric conditions in which our species
evolved. But now,
• We burn fossil fuels to CO2, currently at the rate of 7.7×1015 grams
(7.7 Pgm = petagrams) of C per year.
• Concrete manufacturing adds another 0.3 Pgm/yr of C in CO2.
• This is about 4% of the annual traffic of carbon among the air,
plants/soil, and the ocean,
• and is added too fast to be taken up completely by plants and the
ocean, so 70-80% of it stays in the atmosphere.
19 November 2015
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Destruction of habitability (continued)
 The concentration of CO2
in the atmosphere is
accurately measurable
for about 400,000 years into
the past, using air bubbles
trapped in ice.
 Such measurements
show that atmospheric
CO2 has increased very
sharply since the Industrial
Revolution, and is now the
highest on record.
Woods Hole Research Center; see also Le
Quéré et al. 2009.
 The increase can be confidently be ascribed to fossil-fuel burning.
19 November 2015
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Destruction of habitability (continued)
Why is this a worry?
Two reasons:
 Dissolved CO2 is
reducing oceanic pH
significantly and
steadily.
Doney et al. 2009
• In concert with
this acidification
has been a decline in many aquatic species – in particular many
species, like corals, that are involved in turning carbonate ions
into carbonate minerals.
These data, from the Laboratory for Microbial Oceanography at the
University of Hawaii, can be found here.
19 November 2015
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Links to these data: ocean temperature 1800-date, ocean
temperature AD200-date, Mauna Loa atmospheric CO2, icecore bubble CO2,
19 November 2015
360
0.5
Mann & Jones 2003
MacFarling et al. 2006
0.4
0.3
0.2
340
0.1
0
320
-0.1
300
-0.2
-0.3
280
260
-0.4
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700
1200
-0.5
1700
0.5
Year
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Astronomy 106, Fall 2015
-0.4
1850
1900
NH mean ocean temperature - 16 C
380
1950
2000
NH mean ocean temperature - 16 C
 There is no previous global
warming of the observed
magnitude for hundreds of
thousands of years.
Atmospheric CO2 concentration, ppmv
 More famously, the global
surface temperature – which
is also measurable for the
past several hundred
thousand years – has
increased also increased to
historic highs over the last
100+ years in step with the
atmospheric CO2 increases.
Atmospheric CO2 concentration, ppmv
Destruction of habitability (continued)
-0.5
Year
23
Destruction of habitability (continued)
 If the current trend of oceanic pH keeps up, a substantial fraction of
ocean life will die, and the global food chain will collapse, on a
relatively short time scale.
 If global warming keeps up, the polar icecaps will vanish -- raising
the sea level by hundreds of meters – and vast areas at low latitudes
will become uninhabitable.
• Gains in habitable area at the poles would not offset losses at low
latitudes.
 Global warming is caused by the greenhouse effect of the additional
atmospheric CO2. It is possible, though considered unlikely, that a
runaway greenhouse effect could result from putting a large fraction
of the underground carbon back in the atmosphere.
• That would make Earth like Venus: permanently uninhabitable.
19 November 2015
Astronomy 106, Fall 2015
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Destruction of
habitability
(continued)
At the rate we’re going
With stringent controls
IPCC #5
19 November 2015
Astronomy 106, Fall 2015
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The greenhouse effect: a primer
As we saw early in the semester
(9 February 2012) the planets
emit most of their light at
infrared wavelengths.
 The rocky planets would all
be brightest near a
wavelength of 10 µm.
 Solar heating arrives mostly
at visible wavelengths,
where the atmosphere is
transparent.
Created for Global Warming Art by Robert A. Rohde
19 November 2015
Astronomy 106, Fall 2015
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The greenhouse effect (continued)
 Infrared light is absorbed
very strongly by molecules
in the atmosphere, notably
by water and CO2.
• Some CO2 traded for
methane (CH4) in
animals and decaying
vegetation.
Created for Global Warming Art by Robert A. Rohde
19 November 2015
 Light from the surface can
only escape directly to
outer space through
“windows”, of which the
most important lie at
wavelengths 8-13, 4.4-5,
and 3-4.2 µm.
Astronomy 106, Fall 2015
27
The greenhouse effect (continued)
 Increasing CO2 per H2O in
the atmosphere tends to close
the 3-5 and 8-13 µm windows.
• Methane absorption also
narrows these windows,
but CO2 is the big
malefactor.
 Hotter blackbodies shine
more at shorter wavelengths,
so if not enough light escapes
at 3-5 and 8-13 µm, the
surface heats up until enough
of the emission leaks out in
the shorter-wavelength
windows.
19 November 2015
Created for Global Warming Art by Robert A. Rohde
Astronomy 106, Fall 2015
28
The greenhouse effect (continued)
Water produces the strongest greenhouse effect. If there’s liquid water
on the surface, water’s greenhouse effect can be self-stabilizing, as water
droplets form clouds that reflect sunlight – depending upon the altitude
at which the clouds form. (CO2 and CH4 form neither droplets nor
clouds.)
If temperature rises,
→ more water evaporates into atmosphere
→ more clouds form
→ albedo increases
→ less sunlight reaches surface
→ temperature drops.
And vice versa.
On Venus, sunlight and the greenhouse effect was sufficient to evaporate
all of the water, leaving no liquid bodies on the surface: all water and all
CO2 stayed in the atmosphere.
19 November 2015
Astronomy 106, Fall 2015
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The greenhouse effect (continued)
 Under solar ultraviolet illumination, water molecules high in the
atmosphere dissociate readily, producing atomic hydrogen and
oxygen.
• Oxygen goes on to react rapidly with other molecules; hydrogen,
not so much.
 Hydrogen is too light to be retained by Venus’s gravity (or Earth’s),
so it escaped, relatively quickly.
• Soon there was no more water, or possibilities for making any
more water: a dead world.
• And all the carbon and oxygen wound up in CO2, the atmosphere
pressurized, and the greenhouse effect cranked up to 735 K: a
sterilized world.
19 November 2015
Astronomy 106, Fall 2015
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The greenhouse effect (continued)
Latest estimates for greenhouseeffect increase with increasing
atmospheric CO2 (Ramirez et al.
2014):
 Burning all of our gas, oil and
coal reserves at the present rate
would increase atmospheric
CO2 by a factor of 12, possibly
raising the surface temperature
to about T = 500 K (440 F).
Burning all the fossil fuels
 This would sterilize the Earth
but would not lead to a loss of
the planet’s water. Life could
try again some day.
19 November 2015
Astronomy 106, Fall 2015
Favored relative-humidity feedback
Standard relative humidity
No relative-humidity feedback
31
What do you think will get us first?
:30
A. Killing the oceans.
B.
Melting the icecaps and
restricting habitats to the poles.
Runaway greenhouse effect.
D.
All of the above will happen in
rapid sequence.
E.
None, as we’ll prevent them.
F.
Who cares, the robots will have
taken over by then.
19 November 2015
Astronomy 106, Fall 2015
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