We investigated Arrakis using a climate model, a computer program similar to those used to give weather forecasts. We found the world that Herbert had created, well before climate models even existed, was remarkably accurate—and would be habitable, if not hospitable.

However, Arrakis wasn't always a desert. In Dune lore, 91% of the planet was once covered by oceans, until some ancient catastrophe led to its desertification. What water remained was further removed by sand trout, an invasive species brought to Arrakis. These proliferated and carried liquid into cavities deep underground, leading to the planet becoming more and more arid.

To see what a large ocean would mean for the planet's climate and habitability, we have now used the same climate model—putting in an ocean while changing no other factors.

When most of Arrakis is flooded, we calculate that the global average temperature would be reduced by 4°C. This is mostly because oceans add moisture to the atmosphere, which leads to more snow and certain types of cloud, both of which reflect the sun's energy back into space. But it's also because oceans on Earth and (we assume) on Arrakis emit "halogens" that cool the planet by depleting ozone, a potent greenhouse gas which Arrakis would have significantly more of than Earth.