Muir Glacier and Inlet (1895)

In the photo above, the west shoreline of Muir Inlet in Alaska's Glacier Bay National Park & Preserve is shown as it appeared in 1895. Notice the lack of vegetation on the slopes of the mountains, and the glacier that stands more than 300 feet high. See the glacier as it looked in 2005 on the next page. (USGS/Bruce Molnia)

Photographing Alaska's stunning landscapes has been a passion of Bruce Molnia's since the first time he visited the 49th state, as a Cornell University graduate student in the late 1960s.

While studying for his Ph.D. in geology – which would later lead him to a storied career with the U.S. Geological Survey in coastal, glacial, and ocean research – he came across the photos taken by the earliest American explorers of Alaska back in the early 1880s.

It was these photos – taken by everyone from John Muir in 1879 to later explorers like William Field and National Geographic's Bradford Washburn – that Molnia would use when he was asked in 1999 by then-Interior Secretary Bruce Babbit to find "unequivocal, unambiguous" proof that climate change was real.

Bruce Molnia

Since his first visit in 1969, Molnia has returned to Alaska "probably 300 times," he says. On nearly every visit, he has made expeditions of his own to recreate the photos taken by Muir and others, from their exact same vantage points.

Molnia spoke with weather.com about the work he's done over the last 14 years, and what it means to our understanding of how Earth's climate is changing today. The stories and thoughts below were captured during our conversation with him:

I started out with wow, look how the glaciers are changing. But it became pretty clear after the first or second year of doing this, that it wasn’t only the glaciers you could document changing. To me, the most remarkable thing was how quickly ecosystems became established in areas where the early photograph shows nothing but bare bedrock.

This all began in September 2000, when I spent a week with a team of four people in Prince William Sound. We visited about 15 locations where I had found historical photos from the early decades of the 20th century.

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This was before we had Google Earth to help us. Some of [the photos] I knew were going to be impossible to attempt to duplicate because of the locations, and others because when I had been in those general areas, the vegetation was so dense that I knew you would never be able to see from that original photo point.

But many of them were [taken] standing on the shoreline, or from the top of a ridge. So that was my premise: Finding sites where there was a good enough image that you cold then look at a map and figure out which peak on the map was which peak on the photo, and where the photo might have been taken from.

That was what prompted me to think, I have enough historical images that I could do this. To me, understanding the obvious – the photographic pairs – was the best mechanism to present irrefutable, non-judgmental, unambiguous, unequivocal visual documentation that climate change was both real and underway.

There are so many late 19th-century photos because of John Muir. Once he publicized it, steamers started making their way up to coastal Alaska. This corresponded to a time when Eastman-Kodak was making available handheld cameras that people could take with them that were pre-loaded with up to 100 exposures.

The Pederson Glacier in Alaska's Kenai Fjords National Park, viewed between the mid-1920s and 1940s (on the left) and in August 2005 on the right.

(USGS/Bruce Molnia)

In the photo pairs, the landscape goes from black and white, to blue and green. I have a photo that was taken in 1941 of the Muir Glacier. We went back in 2004 and the vegetation was so dense I couldn’t get my field assistants out onto this bedrock ridge that is in the foreground of this picture.

In the photographer's notes for the photo, he said you go to this particular creek, you walk up the creek, you walk up this rise ... and you’ll be there in 15 minutes. We went to the creek, and the alder was so dense that you were literally pushing each branch out of the way and stepping over them to be able just to go up in the stream bed.

It took us almost six hours to get from where we started, which was probably a distance of less than two miles. Because the vegetation was so dense, you couldn’t even see the sky.

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To understand climate change, we have to look at what climate’s done for the last 1,000 years. Beginning about 900 years ago, we experienced a global cooling event that triggered the Little Ice Age. In Alaska, glaciers expanded dramatically, and many glaciers filled fjords.

At the peak of the Little Ice Age, there were probably 200 ice-calving [glaciers] in Alaska. Since then, we have seen more than 99 percent of the more than 2,000 glaciers in Alaska begin to actively retreat, and continue to retreat up to the present. We’ve gone from over 200 tidewater-calving glaciers to less than 50.

About a dozen years ago, someone caught a marlin off the coast of southeastern Alaska. How could that be? The fishermen tell me that in Prince William Sound, for years now, they have seen a major influx of sand sharks and other species that were not native and are out-competing the fishermen for bottom fish, like halibut - and for crab. And so the ecosystem is rapidly changing.

The simplicity of the photos is so striking. My basic premise is, if a picture’s worth a thousand words, what’s a pair of photos showing dramatic change worth? And that clearly is the message I’m trying to convey.

See more at USGS: Glacier and Landscape Change in Response to Changing Climate