Home Science Sea Level As rising seas erode shorelines, Tasmania shows what can be lost.

As rising seas erode shorelines, Tasmania shows what can be lost.

ISLE OF THE DEAD, Tasmania — Maybe the hardened convicts who carved the 19th-century gravestones dotting this tiny island were barely literate, or perhaps one of them just had a wicked sense of humor. The schoolmaster Benjamin Horne went to his repose in 1843 with this sentence chiseled above his head: “Sincerely regretted by all who knew him.”

If he ever managed to sleep peacefully beneath that pungent epitaph, Mr. Horne can rest no longer.

The very island on which he lies is being chewed away by the sea. The roots of trees that have stood for decades now dangle perilously over a fast-eroding shore. A few miles away, a seaside coal mine once worked by the convicts is under similar assault by the waves.

The ocean is rising in large part, of course, because people the world over have burned so much coal, pumping planet-warming carbon dioxide into the air. Perhaps a new stone marker ought to be planted above the eroding mine: Cause, Meet Effect.

Chris Sharples, a coastal consultant, has lately been spotting such problems all over southern Tasmania, including once-sturdy electric poles in danger of falling over as the ocean strips the land away. Under a brilliant sky, he walked the shoreline near the historic mine one recent day and pointed to a steep scarp cut by the waves, a bellwether of recent damage.

“It’s a smoking gun for sea-level rise causing an acceleration of erosion,” he said. “And it’s coal! Mined for burning!”

Both the imperiled island cemetery and the coal mine are part of the Port Arthur Historic Sites, in the far southeastern corner of Tasmania, the Australian island state. Convict ancestry was once a badge of shame in Australia, but now it is bragged about, and Port Arthur, a 19th-century prison that received some of the most incorrigible criminals in the British Empire, has become one of the country’s premier tourist attractions.

It is also under costly siege by a rising sea, and Port Arthur is but one example of a looming global problem.

In country after country, managers of national parks and other historic sites are realizing that climate change, with its coastal flooding and erosion, rising temperatures and more intense rainstorms, represents a profound risk to the heritage they are trying to preserve.

Venice, home of architectural and artistic masterpieces, is under such grave threat that $6 billion worth of sea gates are being installed to protect against increased tidal flooding. Rising temperatures seem to be on the verge of wiping out large sections of the Great Barrier Reef in Australia. Coastal erosion threatens scores of treasured sites in Scotland, including the spectacular Neolithic ruins of the Orkney Islands. The famed statues of Easter Island are in danger.

In the United States, most of the glaciers that in the 19th century dotted what is now Glacier National Park have already melted, and the rest are expected to be gone within this century. Archaeological sites on the Alaska coast are being lost. The very symbol of America, the Statue of Liberty, cannot be considered safe: Flooding from Hurricane Sandy, made worse by a century of sea-level rise, destroyed much of the infrastructure on Liberty Island in 2012 and closed the monument to visitors for months.

Like so many other problems associated with climate change, this was a crisis foretold.

In a report in 2007, the staff of the World Heritage Convention, an arm of the United Nations that oversees listings of heritage sites, warned of the peril from human-caused climate change. It specifically pointed out the risk to coral reefs, including the Great Barrier Reef.

When the group wanted to update its report in 2016, the conservative government of Australia, under fierce attack at home for the perceived weakness of its climate policies, demanded that any mention of the Great Barrier Reef be stripped out of the new version. The United Nations complied, though the suppressed material quickly leaked.

In the very year that controversy played out, the reef suffered profound damage from high water temperatures, fulfilling the prophecy of a decade earlier. And the same sort of damage is occurring again this year, part of an unprecedented back-to-back die-off that may leave large segments of the reef in ruins.

Rising ocean temperatures and rising sea levels are two sides of a coin: Most of the excess heat trapped by human emissions of greenhouse gases is absorbed by the ocean, and the water expands as it warms, accounting for much of the rise in the sea over the past century. It has gone up about eight inches since 1880, which sounds small, but has been enough in some places to cause extensive erosion, forcing governments to spend billions to cope. The problem is worse in places where the land is also sinking, as in Venice and along much of the East Coast of the United States.

Over the long term, the rise of the sea appears to be accelerating because of runaway growth in greenhouse emissions, and scientists fear much bigger effects this century, perhaps so large they could ultimately force the abandonment of entire coastlines.

Though awareness of the risk to historic sites and natural wonders is growing, the effort to tackle the problem is in its infancy. In most places, discussion and report-writing have yet to give way to concrete action. “We’re a long way from managing this issue well,” said Adam Markham, who is deputy director for climate and energy with the Union of Concerned Scientists, an American group, and who was the lead author of the most recent report on world heritage sites.

Much could be done to shore up old buildings, but that is invariably expensive — and most park services and heritage agencies are badly underfunded. Beyond money, the agencies face deep philosophical issues. How far will they ultimately be willing to go to salvage buildings or parks at risk? Should they, for instance, build sea walls that would forever alter the character of old forts or other coastal sites?

In Tasmania, the archaeology manager of the Port Arthur Historic Site Management Authority, David Roe, wrestles with such questions. The historic site has spent $5 million reinforcing old prison buildings, which are under attack by the rising salt water in the soil and also vulnerable to wind damage. But Dr. Roe is reluctant to consider more aggressive solutions, like a sea wall that would isolate the site from the ocean that connected it to a once-mighty empire.

As he sees the matter, to build such a thing would be to undermine the cultural value that made the place worth preserving.

“We can’t retreat” from the rising sea, Dr. Roe said. “We can’t elevate. We can’t rebuild. Perhaps all we can do is manage loss.”

David Luchsinger was in charge of the Statue of Liberty for the National Park Service when Hurricane Sandy ravaged Liberty Island in 2012, and he led the team that brought the park back to life on July 4 the following year. Mr. Luchsinger, retired and living in New Hampshire, said the issue with historic sites was not just finding the money to make them more resilient, but also slowing the emissions that are putting them at risk in the first place.

“To turn a blind eye on how sea-level rise and climate change are going to affect preserving our history is just, to me, unacceptable,” he said. “That’s where we come from. That is who we are.”