In the early hours of March 24, 1989, the channel connecting the Alaskan port of Valdez with Prince William Sound was riddled with icebergs shed from the deteriorating Columbia Glacier, a massive river of ice that had begun breaking apart only a few years earlier.

With an inexperienced third mate guiding the massive tanker, the Exxon Valdez swerved out of its designated shipping lane to avoid the ice. It was a standard maneuver.

But this time, on this night, before the third mate could correct course, the tanker careened into the outcropping of Bligh Reef, where it ultimately released roughly 11 million gallons of crude oil into Prince William Sound.

That such a catastrophe might happen was not news to the company.

Beginning in 1975, the U.S. Geological Survey had warned Exxon and its co-investors in the Trans-Alaska Pipeline System that the glacier was becoming unstable.

What was triggering the glacier to drop icebergs at such a ferocious and ultimately disastrous pace was unclear at the time. But some scientists, even then, were beginning to look at climate change's role.

In 1978, a news article in the scientific journal Nature reported that the USGS was "concerned that the glacier could, as a result of changing climatic conditions, experience a 'drastic retreat' which might result in … a major hazard to shipping."

In the decades following the accident, as Exxon publicly questioned the risks climate change posed both to society and its own operations and assets, a growing number of glaciologists identified climate as a factor in one of world's largest and costliest environmental disasters.

While glaciers grow and retreat over decades and centuries, most of the planet's glaciers are now shrinking at unprecedented rates, leading scientists to conclude with confidence that a changing climate is the culprit.

"There is no question now that climate change is responsible for both the initial breakup" of the glacier, due to decreased precipitation in the region and its "continued retreat due to higher global temperatures," said Wendell Tangborn, a retired USGS geologist who studied the Columbia Glacier.

The Exxon Valdez oil spill was one of the earliest and most devastating examples of the risks posed by a changing climate, many scientists now say — one that ultimately resulted in the polluting of a pristine sound and the destruction of local fisheries, and cost Exxon a total of $3.4 billion through 2008 in cleanup costs and court settlements.

A number of factors, including an inebriated captain who had retired to his stateroom, an overworked crew and lax regulatory oversight, led to the accident. But it was the icebergs from the deteriorating glacier that created the treacherous conditions that forced the ship to veer off course.

For the two decades following the Exxon Valdez disaster, the company worked quietly to safeguard its operations and infrastructure against steadily rising sea levels and thawing permafrost. Yet in public, it fought regulations and policies that would have limited fossil fuel emissions, while publicly questioning the science behind climate change.

Investigations into the company have been launched by attorneys general in California, New York, Massachusetts and elsewhere concerning its disclosure of climate risks to shareholders for decades.

Alan Jeffers, an Exxon Mobil spokesman, called findings as false and misleading, and said in an e-mail that on the issue of the glacier, there is no "causal link between the Valdez oil spill and climate change."

"As we have stated many times, Exxon Mobil believes the risk of climate change is real and warrants action," Jeffers said in another e-mail.

The trail that led to the Exxon Valdez disaster began in 1968, when Humble Oil, one of two companies that would consolidate to form Exxon, discovered a massive reservoir of crude oil in the Alaskan Arctic.

To get some of those 25 billion barrels to customers, Exxon and its co-investors joined forces to build an 800-mile-long pipeline stretching from the oil field in Prudhoe Bay to Valdez. A year into construction, on Aug. 25, 1975, a glaciologist for the U.S. Geological Survey created a stir with an appearance on the NBC nightly newscast. "Valdez was picked as a pipeline terminus because that bay is open year-round," said Tom Brokaw, the network anchor. But, he added, "that may not always be the case."

The glaciologist, Austin Post, told viewers the glacier was likely to begin a drastic retreat resulting in "a massive ice pack moving out into Prince William Sound." In other words, it was a major threat to the oil tankers navigating the Valdez waters.

In December 1983, the glacier began its predicted retreat.

The ice in the channel connecting Prince William Sound and the port of Valdez was a particular hazard on the night of March 23, 1989, as the Exxon Valdez departed from Valdez.

Radar spotted ice ahead, and Capt. Joseph Hazelwood ordered the ship to leave its lane to avoid the icebergs. "Once we're clear of the ice out of Columbia … we'll give you another shout," Hazelwood radioed to the Coast Guard.

Instead of waiting on the bridge, Hazelwood left his third mate in charge.

The third mate never maneuvered back into the shipping lane, and the tanker slammed into Bligh Reef. The oil spill was an unprecedented disaster environmentally and for Exxon's bottom line.

Today, the Columbia glacier has receded more than 12 miles from its position in 1980, and has lost about half its thickness, according to a 2014 NASA report. Scientists estimate it is has contributed to nearly 1 percent of global sea level rise.