Thanks to SPACEVIEWS for this report,

Venus Subject to Radical Climate Changes The cloudy, extremely hot atmosphere of the planet Venus may have undergone dramatic changes that may also be possible on the Earth, University of Colorado scientists reported Thursday, February 18.

In an article to be published in the March issue of the magazine Scientific American, Colorado planetary scientists Mark Bullock and David Grinspoon outlined a model of the planet's atmosphere that may have had the cloud-shrouded planet free of clouds as recently as 30 million years ago. Bullock and Grinspoon trace their model back 800 million years, when a massive volcanic event resurfaced the entire planet, dumping enough lava to pave over the planet to a depth of 10 kilometers (6 miles). That volcanic event also released large amounts of water vapor and sulfur dioxide, both greenhouse gases.

While those gases would have initially warmed the planet, they would also have formed clouds that would have blocked out the Sun, eventually cooling the planet, cooling the planet down to nearly 90 degrees Celsius (200 degrees Fahrenheit).

As the planet cooled, the water vapor clouds rose through the atmosphere, where sunlight would have disassociated them, allowing hydrogen to escape. The sulfur dioxide would have returned to the surface. As the planet warmed up again, the clouds cleared out, leaving the atmosphere clear 200 million years ago. Bullock and Grinspoon believe the planet remained clear for more than 200 million years, until volcanic activity started up again no later than 30 million years ago, throwing more material into the atmosphere to form the thick cloud deck seen today.

"Our model shows Venus has changed dynamically in the recent past," Bullock said. "Since Venus and Earth have a number of similarities, there are implications here for our own future." Radical changes in climate are not unheard of on the Earth, Grinspoon said, pointing to data from ice cores that show changes of over 10 degrees Celsius (18 degrees Fahrenheit) in less than a decade.

Eventually, though, Earth and Venus will resemble one another, as increased energy from the Sun evaporates the Earth's oceans and triggers a runaway greenhouse effect in about one billion years they said. "In the long term Earth's fate is sealed."