Two climate activists made a beeline for a beautiful Monet painting exhibited at the National Museum in Sweden on a recent Wednesday morning. They wanted to convey the urgency of the environmental crisis — pollution, global warming and other man-made disasters — that could turn the artist’s gorgeous gardens at Giverny into a distant memory. So the young protesters followed what has become a familiar playbook: gluing a hand to the artwork’s protective glass and smearing it with red paint.

In April, at the National Gallery of Art in Washington, two eco-activists splattered paint on the case surrounding a 19th century Degas sculpture, “Little Dancer Aged Fourteen,” drawing pine trees and frowny faces onto its plinth with red and black paint — symbolic of blood and oil.

Similar scenes have unfolded at more than a dozen museums over the last year, leaving cultural workers on edge and at a loss for how to prevent climate activists from targeting delicate artworks. Just last weekend, the Metropolitan Museum of Art in Manhattan was targeted for the second time, as more than 40 activists occupied galleries, silently holding signs that proclaimed “No art on a dead planet.” Meanwhile, the costs for security, conservation and insurance are growing, according to cultural institutions that have experienced attacks.

In some cases they are suing the activists for the damages. In February, Viennese prosecutors dropped their case against protesters who doused a 1915 Klimt painting at the Leopold Museum in black liquid after the demonstrators agreed to pay about $2,200 in damages for the cost of art handling, cleanup and repairing the gallery wall.

But the museum’s director, Hans-Peter Wipplinger, told The New York Times that the Leopold continues to incur the financial repercussions of the climate protest in November 2022. The museum has had to add two additional staff members to its entrance, which has increased operational costs by roughly $32,800, while the price of further glass protections amounts to about $11,000. Wipplinger also said that insurance costs “have risen markedly” on important paintings that draw crowds.

Cultural institutions are attempting to be proactive, when their budgets allow. At the Metropolitan Museum of Art, more security has been added to certain exhibitions, including the current blockbuster, “Van Gogh’s Cypresses.” Lisa Pilosi, head of objects conservation at the Met, said in an interview that every artwork — more than 40 paintings and prints — is behind protective glass because of concerns about climate activists. (Last year, protesters threw soup at a Van Gogh painting at London’s National Gallery.)

“We used very high-end plexiglass because we didn’t want to deal with attacks,” she explained. “But the glass is there to prevent people from touching the works, not to prevent the liquids from dripping down.”

Returning a painting to its former glory after attacks can require hours of careful conservation work, and expensive glass cannot wholly prevent liquids from seeping through the protective barrier.

“We knew something like this could happen,” said Per Hedström, interim director of the National Museum in Sweden. “We had started working on a plan last fall.”

Hedström said that his museum is still calculating the cost of damages that the government might request in prosecuting the activists, who belong to the environmental organization Aterställ Vatmarker (Restore Wetlands).

The number of workers required to clean a painting like the Monet “is actually quite big,” Hedström said. “We had about 10 or 15 people working for a couple of days: conservators, press officers, curators.”

But there are limited options for a state-run museum like his to prevent an attack. “An extreme consequence would be to close the museum,” said Hedström, though that was unrealistic, he admitted, since the collection belongs to the Swedish public. “Activists are using the principles of an open society as a vulnerability.”

In what appears to be a tipping point in the United States, prosecutors have brought serious federal charges against protesters who threatened the safety of art at the National Gallery of Art in Washington, which is a federal institution. Last month, Joanna Smith and Tim Martin, both 53, were charged with conspiracy to commit an offense against the U.S. and damaging a National Gallery exhibit after they smeared paint on the case surrounding the fragile beeswax sculpture of “Little Dancer” in April. Each charge carries a statutory maximum sentence of five years in prison and fines of up to $250,000.

Climate activists have called the sentence “unjustly harsh.” “It was not a call for everyone to rampage museums,” Smith said in a phone interview, adding that she thought the charges would suppress free speech. “It was a call for people to look deeply and think about what they cherish on Earth and what they can do to protect those things.”

Kaywin Feldman, the National Gallery’s director, said she appreciated work done by the authorities “to bring these serious charges.”

After the attack, nearly two dozen employees worked to clean the gallery, examine the sculpture and repair its vitrine, which Feldman said suffered about $2,400 worth of damage. The Degas artwork was removed from the galleries for a total of 13 days. Feldman said that conservators were less concerned by the paint splatters and more concerned by the heavy vibrations caused by the commotion. The sculpture’s delicate wax body can develop cracks from such movements, which is why the museum rarely moves, and never lends, the artwork. The last time the sculpture was moved was in 2020 for an exhibition.

“People keep saying to me: What on earth does Degas’s ‘Little Dancer’ have to do with climate change? Of course, the answer is nothing,” Feldman said. “Museums have always been committed to offering the greatest amount of access possible to original works of art and it has been part of its founding ethos. It bothers us all to have to put up more and more barriers.”