This false-colour ultraviolet image of the south pole of Venus was taken by the monitoring camera on board ESA's Venus Express in 2008. (ESA/MPS/DLR/IDA)

Computers simulating high-altitude clouds of sulphur dioxide blanketing Venus are giving scientists pause over a theory that introducing a sulphur haze over Earth could help combat global warming here.

The European Space Agency’s Venus Express probe first discovered a thin, high-elevation mist of sulphur dioxide covering Venus in 2008. The layer baffled researchers, who reasoned that all traces of sulphuric dioxide should have been destroyed at such heights by the sun’s radiation.

While the clouds on Venus typically form at 50 to 70 km above the surface after volcanic eruptions, the mysterious layer observed by researchers hovered at about 90 to 110 km.

The new computer models built by Xi Zhang, a graduate student at the institute’s Division of Geological and Planetary Sciences at the California Institute of Technology, showed that some droplets of sulphuric acid may evaporate at high altitude, thus freeing gaseous sulphuric acid. The gas rises to greater altitude before being broken apart by sunlight and releasing sulphur dioxide gas.

“We had not expected the high-altitude layer, but now we can explain our measurements,” Hakan Svedhem, the ESA’s Venus Express Project Scientist, said in a release.

“However, the new findings also mean that the atmospheric sulphur cycle is more complicated than we thought.”

This new understanding has implications for geo-engineering on Earth, as it was once believed that sending an artificial sulphur layer in the atmosphere would create a protective haze here that could reflect the sun’s runs, thus cooling the planet. That proposal, from Nobel Prize-winning chemist and meteorologist Paul Crutzen, may have to be re-evaluated.

Scientists do not yet know how quickly that protective layer would be converted back into a gas that cannot block the sun’s rays.

Jean-Loup Bertaux, the principal investigator of the SPICAV sensor on Venus Express, called for further study for applications at home.

“We must study in great detail the potential consequences of such an artificial sulphur layer in the atmosphere of Earth,” he said.