Theme 9 – Venus and Global Warming
ASTR 101
Prof. Dave Hanes
Enigmatic Venus
a near-twin of Earth in size and mass
Cloud-covered, hard to
study. Imagination run riot!
Goddess of Beauty?
Or Hellish Reality?
Hot Enough to Melt Lead
Other Unpleasant Features
The atmosphere is 96% CO2.
The clouds consist of sulphuric acid
droplets; there is acid rain.
The air pressure at the surface
is ~90 x Earth’s. This is like being
1 km deep in the ocean.
(American Seawolf submarines
have an estimated ‘crush depth ’
limit of about 750 metres)
Runaway Greenhouse Effect
It is NOT the clouds of Venus but rather the thick CO2
atmosphere that has led to the runaway greenhouse effect.
Indeed, the clouds reflect a lot of sunlight (so Venus is
very bright!). The clouds actually reduce the amount of
incoming radiation. Without them, it would be even hotter.
One Surprising Feature
The surface of Venus is the same temperature everywhere,
even though it rotates very slowly (and backwards, too, as
it happens). You might expect the side facing the Sun to
be hot, the other side relatively cool.
By contrast: on Earth,
consider how the soil
temperature changes
over the course of a day:
Why is Venus’s Heat So Uniform?
There are tremendously high winds in the
Venusian atmosphere that serve to redistribute the
heat (but no oceans to do the same).
Runaway Greenhouse Effect
- a Timely Warning for Earth
Venus is hot because of the extreme greenhouse
warming caused by the thick CO2 atmosphere.
The Earth has just as much CO2 as Venus does…
So are we likewise threatened?
NO.
Most of the CO2 on the Earth
is tied up in carbonate rocks
(formed via geochemistry, or
from life-forms – sea shells,
etc). There is also some in
the form of vegetation, or
dissolved in the oceans.
A Complex Cycle
Atmospheric CO2 is Increasing
- and the global temperature as well
Is Nature to Blame?
http://www.youtube.com/watch?v=bgRnVhbfIKQ
Know the Numbers!
“I have flown twice over Mt Saint Helens out on our west coast. I’m not
a scientist and I don’t know the figures, but I have a suspicion that
that one little mountain has probably released more sulphur dioxide
into the atmosphere than has been released in the last ten years of
automobile driving…..”
President Ronald Reagan
Human Activity
1.
Increased release of CO2 (especially from fossil fuels).
1.
Clearing of rain forests, etc.
Other Threats
Global warming will lead to the melting of frozen
tundra, where rotting vegetation will release lots
of methane (CH4) – a more potent greenhouse gas
than CO2 itself.
Predictable Outcomes
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a warmer atmosphere: more energy content, leading to
more extreme weather events, less predictable and more
unstable climate
melting ice caps (Greenland, Antarctica) lead to sea-level
rise, flooding of coastal areas
warmer oceans also lead to sea-level rise (the water
expands with temperature)
change in global weather patterns may lead to extreme
heat, drought and desertification in many areas (e.g.
Australia)
reduced habitats for polar bears, coral reefs, …
Sea Level Change
A Terrifying Sequence
https://www.youtube.com/watch?v=hC3VTgIPoGU
Mediating Factors
1.
A rise in temperature would evaporate
more water in the atmosphere, yielding
more clouds. They would reflect more
light (remember Venus?) and might serve
to moderate the growing greenhouse
effect.
Conversely
2.
Suppose the sun dimmed for some
reason. Perhaps the biosphere would
respond by producing more darkcoloured plants, extensive algae on the
surfaces of ponds and the oceans, etc, to
absorb more light and keep the biosphere
temperature higher.
How Would the
Earth ‘Know’ to Do
These Things? GAIA
This hypothesis has elements of mysticism around it
– almost suggesting a sentient Earth. But there
may be some validity to certain elements of it in a
natural-feedback way. In its most developed form, it
is known as the GAIA Hypothesis, championed by
James Lovelock and Lynn Margulis.
http://www.scienceclarified.com/Ex-Ga/Gaia-Hypothesis.html
A Continuing Concern
Climate change is a hot topic that is as much
political and economic as it is scientific.
I personally believe that the problem is real,
serious, and a consequence of human action.
It would be irresponsible to count on the Earth
itself ‘coming to our rescue’ by putting our entire
trust in GAIA!