Venus: Earth’s “Hot”
Future?
Overview
Similarities to Earth
 Differences from Earth
 Current situations of both planets (recap)
 The “dry” runaway greenhouse effect
 The “wet” runaway greenhouse effect
 How they relate to Earth
 Skeptics of either/or scenarios on Earth
 An example of it already happening
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Similarities
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Orbital radius is 70% that of Earth’s.
Planetary radius is 95% of Earth’s.
One of the inner “rocky planets”
Has similar mass and density.
Surface features of highlands and lowlands.
Abundant atmosphere.
Geological processes still continue (volcanoes,
etc)
Akna Mountains
Venus Northern Hemisphere (radar imaging)
Differences
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Makes one axial rotation every 243 Earth days.
Orbits in retrograde motion.
Tilted 177.4 degrees compared to Earth’s 23.5
degrees.
Atmosphere 90 times more massive than Earth’s.
Very high atmospheric concentration of CO2
Has very low amounts of hydrogen.
Current Situations
Venus:
 Barren wasteland
 Avg. Temp of 900° F
 96.5% of atmosphere
is CO2
 No water
 Clouds of sulfuric acid
 Behaves as it was
expected to
Earth:
 Supports life
 Avg. Temp of 57 ° F
 0.04% of atmosphere
is CO2
 Abundant water
 Clouds of water vapor
 Deviates from
expected behavior
Why is this so?
Venus and Earth both formed
approximately 4.5 billion years ago and
given their similarities, should have turned
out the same, but they do not. Why didn’t
they?
 How is it that Earth can support life when
Venus is completely hostile to it?
 The answer: Global warming.
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Two Runaway Greenhouse Effects
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“Dry” Runaway Greenhouse Effect – no
liquid water.
“Wet” Runaway Greenhouse Effect – liquid
water present.
“Dry” Effect
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Venus was closer to the sun and this proximity didn’t allow water to
condense.
Since no water condensed, carbon dioxide could not be taken out of
the atmosphere by oceans.
Outgasing from the planet (through volcanoes) would continue to
increase amounts of CO2 and water vapor in the atmosphere.
This heating leads to whatever water vapor present to rise to the
top o the atmosphere.
It is broken in oxygen and hydrogen molecules by ultraviolet light.
Lighter hydrogen escapes into space, oxygen left recombines with
other elements like sulfur and oxygen.
The planet loses hydrogen, and in effect loses all the water it had
and becomes the inferno that it is today.
“Wet” Effect
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The water on Venus did condense into oceans.
Higher temperatures than Earth would cause it to evaporate large
amounts of water into the atmosphere.
It would not precipitate back since the temp. was so high and
oceans gradually vanished.
The higher temperature also caused rocks to hold carbon less
effectively and carbonates would eventually undergo processes
releasing their stored carbon.
As more water vapor enters atmosphere, the temperature rises even
more and when the oceans were completely gone, water vapor
again starts to rise to the top of the atmosphere
They are then broken up by ultraviolet rays and hydrogen escapes
into space while oxygen remains and recombines.
The planet STILL loses all its water even if it once had liquid oceans.
Earth’s Greenhouse Effect
Greenhouse gases on Earth, carbon
dioxide, methane, ozone, and water vapor
raise the temperature of the planet.
 Without the greenhouse effect, the planet
would be -13° F, with it, it is about 55 ° F.
 Most of the greenhouse effect comes from
carbon dioxide which is responsible for
57% of the total.
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Venus Relevance to Earth
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Human activity is increasing greenhouse gas
concentrations.
Every year 6 billion tons of carbon dioxide alone
are put into the atmosphere.
In the past 133 years, avg. global temp. has
risen by 0.5° C or 1 ° F.
By 2100 it is expected to rise anywhere from 1.5
° C to 5.5 ° C (2.7 ° F to 10 ° F)
This may or may not be enough to trigger a
“Wet” Runaway Greenhouse Effect
Venus Relevance to Earth (cont.)
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A “Wet” Runaway Greenhouse Effect on Earth would require that
the majority of the oceans around the world evaporate more water
than they get back through precipitation.
The average temperature where this is occurs is more than 80° F.
Currently, the highest ocean surface temp. at any given time usually
does not rise above 87° F.
The average ocean surface temp. varies between 50° to 60° F
(closer to the 50).
If by 2100 the average global temp. rises by 10° F then the average
surface temperature could possibly rise to about 70° F, this is much
closer to the doomsday number of just slightly over 80° F.
If this process were ever to start, it would be impossible to stop
given the vast energies involved in it.
Venus Relevance to Earth (cont.)
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All the water would evaporate into the atmosphere, fueling more global warming until
all the oceans were gone.
At this point, water molecules in the atmosphere would move closer to the top of the
atmosphere and get broken apart by ultraviolet rays.
The reason ultraviolet rays would affect them more at that point than now is because
there would be virtually no ozone layer left at this point.
Global warming contributes to the destruction of ozone.
Once the water molecules were broken up, hydrogen would escape into space, just
like on Venus and oxygen would remain to recombine with other elements.
If this sounds similar to Venus, it should. Venus, in becoming the 900° F inferno that
it is, follows and expected path of progression while Earth is the anomaly, not the
other way round.
The only things preventing Earth from fulfilling its expected outcome are the carbon
cycle, since oceans remove a great deal of carbon dioxide and keep it in check and
life, since many organisms (such as shellfish) create carbonates in the form of shells
and help take carbon dioxide out of the atmosphere.
This is a very delicate process that can be easily upset.
Skeptics’ Arguments
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Skeptics of either scenario happening have some facts to
try and support their claims.
One compelling argument they make is that carbon
dioxide is only 0.04% of the Earth’s atmosphere and, to
date, humans have contributed only 3% directly.
Although 6 billion tons of CO2 may be released every
year into the atmosphere by humans, 200 billion is
released by natural processes in the same time frame.
But their one flaw is that they fail to realize how fragile
the system is and how narrowly Earth avoided becoming
a second Venus.
A disruption of the carbon cycle that keeps global
temperatures in check could change…
This…
Into…
This!
My planet!
I mean…
This.
Venus (view from space)
Example Already Happening
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In fact, a very localized scenario of the “wet” runaway
effect has already occurred.
In May of 2002, scientists discovered an area in the
Pacific Ocean to the North East of Australia that
exhibited a runaway effect.
This location was warm enough year round to continually
evaporate more water vapor than precipitated back to it.
Luckily, since it is only a localized area, surrounding
parts of the ocean compensate for it. If the entire planet
were to runaway, however, there would be no other
areas to compensate.
This one example shows that we could very well be close
to the entire planet running away.
Conclusion
Action must be taken now to avoid the
Venus outcome happening on Earth.
 If it is indeed the one planet that supports
life, human beings have a great
responsibility to preserve it.
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Hope everyone has a good winter break!
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