Venus' runaway greenhouse effect a warning for Earth

[Sam Carana]

Venus was transformed from a haven for water to a fiery hell by an
runaway greenhouse effect, concludes the European Space Agency (ESA),
after studying data from the Venus Express, which has been orbiting
Venus since April 2006.

Venus today is a hellish place with surface temperatures of over 400°C
(752°Fahrenheit), winds blowing at speeds of over 100 m/s (224 mph)
and pressure a hundred times that on Earth, a pressure equivalent, on
Earth, to being one km (0.62 miles) under the sea.

Hakan Svedhem, ESA scientist and lead author of one of eight studies
published on Wednesday in the British journal Nature, says that Earth
and Venus have nearly the same mass, size and density, and have about
the same amount of carbon dioxide (CO2). In the past, Venus was much
more Earth-like and was partially covered with water, like oceans, the
ESA scientists believe.

How could a world so similar to Earth have turned into such a noxious
and inhospitable place? The answer is planetary warming. At some
point, atmospheric carbon triggered a runaway warming on Venus that
boiled away the oceans. As water vapour is a greenhouse gas, this
further trapped solar heat, causing the planet to heat up even more.
So, more surface water evaporated, and eventually dissipated into
space. It was a "positive feedback" -- a vicious circle of self-
reinforcing warming which slowly dessicated the planet.

"Eventually the oceans began to boil," said David Grinspoon, a Venus
Express interdisciplinary scientist from the Denver Museum of Nature
and Science, Colorado, USA. "You wound up with what we call a runaway
greenhouse effect," Hakan Svedhem says. Venus Express found hydrogen
and oxygen ions escaping in a two to one ratio, meaning that water
vapour in the atmosphere -- the little that is left of what they
believe were once oceans -- is still disappearing.

While most of Earth's carbon store remained locked up in the soil,
rocks and oceans, on Venus it went into the atmosphere, resulting in
Venus' atmosphere now consisting of about 95% carbon dioxide.

"Earth is moving along the curve that connects it to Venus," warns
Dmitry Titov, science coordinator of the Venus Express mission.


References:

Venus Express - European Space Agency (ESA)
http://www.esa.int/SPECIALS/Venus_Express/SEMGK373R8F_0.html

Venus inferno due to 'runaway greenhouse effect', say scientists
http://www.physorg.com/news115477239.html

Probe likens young Venus to Earth
http://physicsworld.com/cws/article/news/32018

European mission reports from Venus
http://www.nature.com/nature/journal/v437/n7062/full/4371071a.html

[Sam Carana]

Over the years, I've discussed ideas to could increase cloud coverage, with the aim of reflecting more sunlight back into space. See the thread at:
http://groups.google.com/group/greenhouseeffect/browse_thread/thread/dea66030b534709c

As discussed, one of my worries is that if water gets up too high in the atmosphere, it will trap some of the light underneath, thus strengthening the greenhouse effect. What worries me even more is the possibility that Earth will start loosing hydrogen and oxygen to space, if we artificially increased humidity. I wrote about this danger in the article below, which was also posted at:
http://www.gather.com/viewArticle.jsp?articleId=281474977189423

Has anyone got more information about this?

Cheers!
Sam Carana