Friday, November 30, 2007

Venus' runaway greenhouse effect a warning for Earth

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. 


Venus Express - European Space Agency (ESA) 

Venus inferno due to 'runaway greenhouse effect', say scientists 

Probe likens young Venus to Earth 

European mission reports from Venus