A handful of science and natural history museums across the globe announced in recent weeks they are cutting ties with the fossil fuel industry, limiting their sponsorship and donations and culling oil and gas stocks from their investment portfolios.

The Field Museum in Chicago—one of the largest natural history museums in the world—quietly announced Friday it has divested its financial portfolio from fossil fuels. The Australian Academy of Sciences said it finished divesting in late October. The California Academy of Sciences and the Phipps Conservatory and Botanical Gardens in Pittsburgh have both divested and instituted new gifts policies that prohibit them from accepting money from oil and gas interests. London's Science Museum said last week it would not renew a sponsorship deal with Royal Dutch Shell.

Earlier this year, a group of climate scientists sent a letter to museum directors arguing such financial ties with fossil fuels could "undermine public confidence in the validity of these institutions." There was a more recent public reaction when The Guardian reported that Shell was sponsoring the London museum's climate change exhibit, and attempting to influence its contents.

"With public money for museums shrinking, they are increasingly reliant on private funds to keep their doors open," said Beka Economopoulos, co-founder and director of the Brooklyn-based Natural History Museum, a new educational organization that coordinated the scientists' letter. "But when the institutions that educate people about science and the natural world, and inspire awe in the natural world, cozy up to fossil fuel industry, they undermine the faith and trust the public places in them."

More than 30 climate scientists signed the letter when it was released in March; there are now nearly 150 signees. Economopoulos and her colleagues have met with dozens of top museum directors about the campaign, manned booths and organized panel discussions at several major international museum conferences. Interest in the campaign, she said, is growing.

The letter "is certainly something that is provoking conversations and serious thinking" in the museum world, said Jonathan Foley, executive director of the California Academy of Sciences. "A few museums (like us) were already on board, and many more were moving in this direction. Others weren't thinking about it, but now are. Others will dig in, and be resistant. It is the same kind of reaction as we're seeing from universities."

The Field Museum divulged their divestment news in response to a tweet from the Chicago branch of 350.org, saying it had "already divested from fossil fuels awhile ago." The museum did not have any additional comment when contacted by InsideClimate News. The decision by The Science Museum in London came to light last week when it responded to a Freedom of Information request from the British activist group BP or not BP?, saying it didn't "have plans to renew its existing sponsorship deal or initiate a new deal or funding agreement with Royal Dutch Shell."

President of the Australian Academy of Sciences Andrew Holmes announced his institution's divestment from fossil fuels—equaling "millions of dollars," according to a press release—in a speech at a climate science conference Oct 27. "Is the value that could be derived from fossil fuel activities sustainable in the long term? Certainly not from the view of the Earth system—and probably not financially either," he said.

The Phipps Conservatory and Botanical Gardens in Pittsburgh also made the recent decisions without much fanfare. Richard Piacentini, the executive director of the museum, confirmed for the first time publicly to InsideClimate News it had decided to divest at the end of October.

"We view this as part of a broad initiative to make sure that all our investments and actions are consistent with everything we're doing," Piacentini said.

The museum, which is located in the heart of Pennsylvania coal and fracking country, instituted a gifts policy banning oil and gas donations two years ago. It has been replacing old structures with LEED certified buildings in recent years and currently offsets 100 percent of its electricity with renewable energy credits.

"To talk so much about energy and renewable energy and climate change on our campus and in our exhibits, it didn't make sense to be sponsored by the fossil fuel industry," he said.

The California Academy of Sciences said it has been working on divesting from fossil fuels since 2014. In January, it announced a new gifts policy prohibiting it from accepting donations from oil and gas companies and by the summer had divested all of its direct investments in fossil fuel companies. The institute is now looking into any indirect fossil fuel investment they have in their portfolio, said Foley.

Despite the progress by museums in the U.S., Australia and Great Britain, many other institutions remain hesitant to break their bonds with fossil fuels.

The Smithsonian National Museum of Natural History in Washington, D.C. and the American Museum of Natural History in New York came under fire after the scientists' letter in March singled them out for their relationships with David Koch, co-owner of the oil and manufacturing giant Koch Industries and a major contributor to climate denial campaigns. Koch is an advisory board member and trustee, respectively, and major sponsor of both museums. Neither has yet moved to cut ties with him.

Economopoulos said many museums argue they need to be objective or neutral when it comes to controversial topics like climate change, because they don't want to alienate any visitors. Others promise there's a firewall between funders and the content in the museums.

But climate scientists and advocates point to several examples that such a firewall doesn't exist. The Perot Museum of Nature and Science in Texas, for example, largely skirts the issue of anthropogenic climate change in its exhibits and failed to hang an approved panel describing the link between the burning of fossil fuels and global warming. Visitors to the museum can see a massive oil drill bit, take a tour of a fracking well, and touch a piece of the Barnett Shale, which has fueled Texas' recent natural gas boom. The institute's major funders include ExxonMobil and the Rees-Jones Foundation, which was created by the founder of Chief Oil & Gas, among other fossil fuel executives.

"Of course where you get your funding affects your programming," Economopoulos said. "When your multimillion-dollar funder's politics are well known, they don't have to be in the room to have an influence."

Museum directors and organizers told InsideClimate News that momentum for the campaign is increasing.

"I've heard more talk about this issue since last spring, there is a lot more awareness," Piacentini said. "I wish I would see a stampede of people already doing the same thing, but it is the kind of thing that will take a little bit more time. The problem is we don't have much time."