In the 18th century, watercolours became a popular way for professional and amateur artists alike to document the landscapes, animals and plants that were important to them. Portable and aesthetically pleasing, watercolours helped bring painters' worlds to life.

Today, these works are precious and unwitting documents of a world altered by the ravages of climate change, overhunting, urbanisation and other human activity. The Watercolour World, financed by the London-based Marandi Foundation, is a free online database of watercolours painted before 1900.

It's the brainchild of Fred Hohler, a former British diplomat devoted to art preservation. His last project, the Public Catalogue Foundation, a charity that is also called Art UK, catalogued all of Britain's publicly owned oil paintings.

This project brings together tens of thousands of art online. The nonprofit organization works with collectors around the world to find and digitise watercolours. It also is on the hunt for other pre-1900 watercolours that document animals, places, plants or events. So far, it has collected about 80,000 images.

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The point isn't just to preserve them - it's to provide their documentary power to researchers.

"With the world at risk from climate change, rising sea levels, and worse, the project will provide scientists and environmentalists with an accurate visual account of much of the natural world as it used to be," Hohler said in a statement.

That visual testimony can be strikingly different from today's world.

For example, a search for "ice" shows chilly landscapes in the Hudson Strait, the Swiss Alps and Antarctica - three places whose ice has waned with the warming climate. The site's founders hope scientists will use the paintings as comparison points as they study phenomena such as coastal erosion and glacial retreat.

The watercolours offer other glimpses into the past, such as a circa 1638 painting of a dodo, an circa 1837 painting of a quagga zebra and an 1885 painting of a huia bird. All are extinct.