Just today, there was an article posted on a site called Spaceflightnow about climate change, where the Earth is compared with Venus and Mars. According to that article, Venus and Mars were originally fairly Earthlike, but later on they suffered climate catastrophes.
The article stresses that Venus has suffered a runaway greenhouse effect. This happened after its atmosphere slowly changed until it reached a point of no return. Since there are no people on Venus polluting its atmosphere, most of the atmospheric change of our sister planet was driven by the steady brightening of the Sun. (The rest of the atmospheric change of Venus may have been caused by heavy volcanism on this planet.)
The article quotes David Grinspoon, one of the scientists working on the Venus Express mission, who says that the changing atmosphere of the Earth, too, may reach a point of no return, after which there will be a runaway greenhouse effect on our planet. Scientists do not yet know how close we are to such a point of no return.
Here is a link to the article:
Climate Catastrophes in the Solar System Ann
