We are all witnesses to climate change's devastating impact on our world. We just have to stop and listen.

It was spring 2004. The air was cool and still, the encroaching dawn light outlined the horizon; and there, in the heart of California’s Sugarloaf Ridge State Park, was Bernie Krause busily setting up his microphone.

The soundscape ecologist recorded the symphony of the forest’s sounds that day: the gurgle of the gushing stream; the melodic birdsong from sparrows and woodpeckers, robins and grosbeaks, towhees and wild turkeys. It was a rich and vibrant recording, a celebration of life and biodiversity.

Krause returned last year to the same spot in Sugarloaf, located a short drive from his Glen Ellen home. The details of the recording session were the same: springtime in early dawn, a microphone and a tripod. But the habitat’s soundtrack had altered dramatically.

“[It was the] first spring in my 77 years that was completely silent,” said Krause. “There were birds. But there was no birdsong whatsoever.” Even the surge of the stream could not be heard.

As Krause explained, the music of the Sugarloaf area had been diminishing for years, silenced in part by California’s record-breaking drought.

“Between 2009 and 2015, under the full impact of the drought, you hear an almost complete lack of density and diversity,” he told Outside magazine in December. “Whether or not it regains vitality remains to be seen.”

Soundscape ecology is the study of nature’s sounds -- from the lapping of the ocean’s waves and the rustle of leaves, to the howls of wolves and the chortle of kangaroos.

“Natural soundscapes are a narrative of place. They contain information vital to our understanding of the natural world,” Krause told The Huffington Post in an email this week. “They provide feedback to us as to how well we are doing in relationship to a given environment, whether it is under stress, or thriving.”

For almost five decades, Krause has devoted his life to documenting the sounds of the world’s many natural habitats. He’s recorded the growls of Amazonian jaguars; the belch of Fijian sea anemones; the groaning of Arctic glaciers; and even the bizarre, beautiful “song” of a cottonwood tree. Since 1968, he’s captured more than 5,000 hours of audio in habitats both terrestrial and marine.

“When I first began recording wild soundscapes, I had no idea that ants, insect larvae, sea anemones and viruses created a sound signature,” said Krause in a 2013 TED Talk about his work. “But they do. And so does every wild habitat on the planet.”

If, however, Krause’s earlier recordings were a chronicle of the Earth’s rich biodiversity, his more recent work is a testament to the planet’s decline.

The soundscapes “speak eloquently to all of the climate issues we are now confronting,” Krause said. “Global warming, severe weather shifts, earlier and later warm seasons, shifts in the density and diversity of bird, frog and mammal populations. All of these factors are conveyed.”

Of the 3,700-plus habitats represented in his archive, more than 50 percent are now either “altogether silent or so radically altered because of human endeavor, that they can no longer be heard in any of their original voice,” Krause said.

“These are soundscapes that no one will ever experience again in their natural state. They exist now only as an abstraction, a digital acoustic impression of what we once had,” he added.

﻿Here's a recording from the Osa Peninsula of Costa Rica, which Krause captured in 1989:

He returned several years later, after the tropical forest had been clear-cut:

Scientists estimate that one-quarter of the world’s species may be driven to extinction because of climate change by 2050. That number could rise to 50 percent by 2100.

“A great silence is spreading over the natural world even as the sound of man is becoming deafening,” Krause wrote in his 2012 book, “The Great Animal Orchestra.” “Little by little the vast orchestra of life, the chorus of the natural world, is in the process of being quietened.”

In July, the Fondation Cartier pour l’Art Contemporain in Paris will launch a special exhibition showcasing Bernie Krause’s work entitled, “The Great Animal Orchestra.” It is the first ever exhibit dedicated to the subject of soundscape ecology, according to Krause. Works by other artists, including Mexican architect Gabriela Carrillo and Chinese artist Cai Guo-Qiang, will also be featured. Find out more about the exhibit, which will run till January 8, 2017, here.