The Role of Biology in the
Climate System:
Long Term Climate Regulation
Earth History, Gaia and Human
Perturbations of Biological Systems
A Brief History of Earth’s Climate
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Earth formed 4.6 billion years ago
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Earth developed a thick CO2-rich atmosphere and a
deep ocean
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Earth, Mercury, Venus and Mars are composed principally
of rock (iron and silicate minerals) from the hot, inner parts
of the condensing nebula
Outer parts of the nebula, icy/volatile (low boiling point)
materials such as water, methane and ammonia condensed
to form Jupiter, Saturn, Uranus and Neptune
Despite lower solar luminosity at the time (ca. 30% lower
– sun brightens as it ages), the earth was warm because of
the intense greenhouse effect
The sun then brightened, and atm CO2 decreased (due
to negative feedback in the weathering cycle) and
climate was maintained at levels favorable to life
Paleoenvironmental
(Past Environment) Indicators
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Biology: fossil record (follow ancient “Holdrige Life
Zones”)
Chemistry: isotopic evidence (e.g. Oxygen, Carbon),
banded iron formations
Physical evidence: e.g. charcoal and evidence for
glaciation (at that location, average summer
temperatures below 0oC)
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Moraines
Striations
Dropstones (ice-rafting)
Tillites
Formation and History of the
Earth's Atmosphere and Oceans
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Impact degassing up to ca. 3.8 billion years ago:
bombardment of the surface by smaller planetesimals
released water, CO2 and other volatile compounds into
the atm
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Also contributions from volcanoes and hot springs
Also contributions to atm from comets and other volatilerich asteroids
Early atm w/o O2, but rich in CO2 (1,000-30,000x
present!), N2, H2S, CO2, HCL, H2O
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High CO2 because small continents (they accrete over time
by plate tectonics)
So no place to store carbon via silicate weathering
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Removal of atmospheric CO2
by weathering
+ (shorter term deposition of
limestone and organic matter on
ocean floor)
Weathering
http://www.uoregon.edu/~jrice/geol_311/Seds.html
Long Term Feedbacks in the
Weathering/Carbonate-Silicate Cycle
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Temperature
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Increased temperature increases reaction
rates, including chemical weathering
Net rainfall
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Increased water increases weathering as water
is required water for dissolution and transport
Increase atmospheric CO2 leading to warmer world,
leading to wetter world, leading to more weathering
thereby decreasing atmospheric CO2
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First evidence of life 3.8 billion years ago: procaryotes,
did not produce O2
 Procaryotes=single-celled organisms w/o nuclei
First procaryotes that did produce O2 evolved around 3.5
billion years ago:
 CO2 + H2O -> CH2O + O2
Oxygen started to accumulate and ozone O3 formed a
protective layer against uv radiation
Increasing oxygen
resulted in
formation of Fe
(iron) deposits 2.2
to 1.6 billion
years ago: the
solubility of Fe in
water is a function
of the oxygen
concentration
Life
Life, continued
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Evidence for higher lifeforms abundant after 600
million years, fossil record, only 13% of Earth's
history! (Cambrian)
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Prior 600 million years ago (Precambrian) very little
preservation
Production of O2 by photosynthesis was balanced by
respiration (reverse of reaction above)
First humans:~4 million years ago, homo sapiens 0.4
million years ago
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An english yard is the distance from the tip of the nose to
the end of the middle finger, one stroke of a file on the nail
would erase the entire history of humankind
“Modern” Conditions
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Over the past few hundred million years, Earth’s climate
has fluctuated between warm and cold conditions,
primarily as a result of these inter-related factors:
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Changes in locations of continents/sea level/mountains
induced by plate tectonics
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http://www.scotese.com/paleocli.htm
http://www.ucmp.berkeley.edu/geology/anim3.html
http://wrgis.wr.usgs.gov/docs/parks/animate/pltecan.html
Changes in atmospheric CO2 related to the carbonate-silicate
cycle and biology
Changes in albedo related to glaciations
Devonian period (410360 Mya): Spread of
vascular plants with deep
root systems and
microorganisms accelerate
weathering and decrease
atm CO2 by increasing the
CO2 partial pressure in
soils and releasing volatile
organic acids that help
dissolve rocks (thereby
taking up CO2)
Carboniferous period
(360-286 Mya):
formation of coal
deposits (from burial of
peat) – buries carbon,
decreasing atm CO2
… Biological influences tend
to decrease atm CO2 and
cause cooling over the past
500 my
Mesozoic Era (251-65 mya =
Dinosaurs)
Faster sea floor spreading
–More subduction of deep sea
carbonates
–Faster release of CO2 through
carbonate metamorphism
–More release of CO2 by outgassing at
spreading ridges
–Higher sea level (because of hot, high
oceans) result in less continental
weathering
No ice at poles for ice/albedo
feedback
…Physical causes for elevated
CO2 and warmer climates
Climate Evolution on
Venus and Mars
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Like Earth, Venus and Mars started with
water, carbon, silicate …
Venus
At first glance, if Earth had
a twin, it would be Venus.
The two planets are similar
in size, mass, composition,
and distance from the Sun.
But there the similarities
end. Venus has no ocean.
Venus is covered by thick,
rapidly spinning clouds that
trap surface heat, creating
a scorched greenhouselike world with
temperatures hot enough
to melt lead and pressure
so intense that standing on
Venus would feel like the
pressure felt 900 meters
deep in Earth's oceans.
These clouds reflect
sunlight in addition to
trapping heat. Because
Venus reflects so much
sunlight, it is usually the
brightest planet in the sky.
http://photojournal.jpl.nasa.gov/jpegMod/PIA00271_modest.jpg
Venus
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Closer to the sun so solar flux at surface of Venus is
1.9x that of Earth
So atmosphere becomes so warm and full of water
vapor that virtually no infrared radiation from the
surface is allowed to escape to back to space
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Runaway greenhouse: surface becomes warmer and
warmer, temperatures as high as 1500 K
Oceans evaporate – all water turns to vapor (so no
silicate weathering) and then is lost by
photodissociation and escape of hydrogen into space
Turns hot and dry with dense swirling clouds of sulfuric
acid
Mars
http://mars.jpl.nasa.gov/gallery/duststorms/20020508a_b.html
Mars
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Solar flux only 43% that of Earth so solar heating so
low that CO2 itself condensed forming clouds and polar
ice caps which are mixtures of CO2 and water ice (CO2
ice = dry ice)
Was once (before 3.8 bya) warm enough to allow liquid
water to flow on its surface
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Terrain: channels/valleys cut by flowing water
http://themis.la.asu.edu/fullimages/20020621a.jpg
Maybe cooled off so quickly because of its small size
and therefore small internal radioactive/”geothermal”
heat source, no plate tectonics
Most of CO2 locked into rocks or ice
http://themis.la.asu.edu/zoom-20020621a.html
Gaia
(Ancient Greek Mythology=Goddess of Mother Earth)
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James Lovelock and Lynn Margulis: Life
itself has been responsible for maintaining
the stability of Earth’s climate
Self regulating by feedback loops
Organisms can be components of selfregulating, natural systems simply because
they influence and are influenced by, the
physical environment in which they live
Daisyworld?
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A world populated entirely by white daisies and gray soil (or black
daisies)
Two component system
 Temperature
 Area of white daisy coverage
More white daisies, more reflectance (higher albedo), cooler
temperatures
But … daisies have an optimum growth band – don’t like temperatures
too hot or too cold (Monday lecture)
If temperatures cool
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Daisies don’t grow as well, leaving enough dark area exposed to absorb
sunlight and maintain the temperature within their optimum range
What if something causes temperatures to warm above the optimum?
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The daisies will die off because it is too warm
Causing more gray area to be exposed, absorbing more sunlight, and
killing more daisies
More on this in Chapter 2
How have/can humans affect(ed) biological systems?
How can these changes in biological systems affect
climate?
Purposeful Use of Biology to Modify
Climate
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Carbon trading/reforestation
Ocean fertilization with iron
Greenroofs
Consider …
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How would this approach work? What aspect of the
climate system is it designed to affect?
Where would it work best?
What are the positive and negative side effects? Include
social as well as climatological (e.g. asthetics)
Is this a good idea? Should it be widely promoted/used?