Called News From the Future, the series of renderings depict famous architectural landmarks in places such as Paris, Rome, New York and London submerged beneath waves or smothered in desert sands.
"I try to imagine what would happen in the event of desertification, the rise of the oceans or the tropicalization of a region," Barrau told Dezeen.
For each composition, he combines drone photography and stock images to imagine how future generations of climate-apocalypse survivors might explore the ruins of major cities hundreds of years from now.
He imagines them experiencing "the same feeling as the archaeologists of the 19th century who discovered Pompeii", the Roman city buried and preserved under ash from a catastrophic volcanic explosion in 79 AD.
Barrau's cinematic photomontages draw inspiration from his favourite works of post-apocalyptic fiction.
The image of two whales swimming above Paris' Arc de Triomphe is a tribute to the French artist Roland Cat, whose work in the 1970s and 80s imagined sea creatures swimming above drowned cities.
News From the Future deliberately evokes films such as Planet of the Apes (1968), Mad Max (1979), Akira (1988), and a 2008 documentary from National Geographic called Aftermath: Population Zero.
The dramatic images are intended as a call to action, Barrau told Dezeen.
"My motivation for this series was how to influence awareness of climate change and the urgency to act every day according to one's means and power," he said.
"In my case, my little power is to create images and imagine myself as an explorer who will return from the future with photos of a changed world," added Barrau.
"I remain convinced that a simple image can have more impact on people, especially the youngest, to understand the probabilities of the consequences of inaction."
Barrau is far from the only creative to use their skills to spread a message about the dangers of climate change.
Los Angeles-based artist Lucy McRae has made a wearable survival suit roaming a post-apocalyptic landscape, and design studio Superflux used renderings to imagine how Singapore might look in 2219.
Images courtesy of Fabien Barrau.