Trails of smoke form an ever-changing black flag in this video footage, created by Irish artist John Gerrard to highlight the threat posed by increasing levels of carbon dioxide in the earth's atmosphere.

The film suggests that the flag is a real installation – but it is actually a lifelike virtual simulation.

It was broadcast on a large screen in the courtyard of London's Somerset House for a week, to coincide with Earth Day back in April.

The setting for the project is Spindletop, a vast oil field discovered in Texas at the start of the 20th century. As the home of the Lucas gusher, which initially produced around 100,000 barrels of oil per day, the site has become synonymous with the Texas oil boom.

Today it is hard to imagine that this site, which is now completely barren, was once a highly valuable piece of real estate.

Gerrard's film, called Western Flag, aims to highlight the contrast between then and now.

"One of the greatest legacies of the 20th century is not just population explosion or better living standards, but vastly raised carbon dioxide levels in the atmosphere," said the artist.

"A new flag attempts to give this invisible gas, this international risk, an image, a way to represent itself. I like to think of it as a flag for a new kind of world order."

Gerrard used real-time computer graphics to create the simulation. It is technically a piece of software, built by converting a comprehensive photographic survey of the site into computer code.

Then, for the duration of the broadcast, the constructed scene was constantly updated using the latest photographic recordings. Live information was fed through by a computer at a rate of 50 frames per second – meaning the view was true to life at every moment.

As a result, viewers were able to watch the sun rising and setting at precisely the right times, and to observe the changing levels of light and shadow across the day.

To match, the simulated flag – a slender pole with seven smoke spouts – didn't repeat itself at any point during the broadcast, in order to be as realistic as possible.

The project is the latest in a series of virtual worlds created by Gerrard, who is based in both Dublin and Vienna, but the first the artist has presented outside of a gallery.

Not only was it viewed by visitors to Somerset House, it was also aired on UK television, on Channel Four, on 22 April 2017.