Thomas Crowther, the ETH Zürich ecologist whose rapid rise to prominence brought him intense media coverage, large research grants, and a position advising the United Nations, blurred personal and professional boundaries and broke rules regarding financial compliance and hiring, according to a report the university released last week. The redacted report—which does not name Crowther but describes particulars that match his case—also notes multiple allegations of inappropriate behavior toward employees. Crowther has been denied tenure as a result of the findings and will leave the institution in September when his contract expires, the university has announced.
ETH Zürich did not reach a definitive conclusion about some of the interpersonal allegations, university Vice President for Personnel Development and Leadership Julia Dannath said in a 25 April online statement that referred to “an ETH assistant professor.” But she says the professor “did not maintain an adequate professional distance from students, doctoral students and staff.” Vice President for Finance and Controlling Stefan Spiegel said the professor “repeatedly failed to follow internal rules and adequately address conflicts of interest.”
In an email to Science, Crowther said he “sometimes blurred the lines between friendship and leadership” but that he had not committed any personal misconduct and if university procedures “were inadvertently not fully respected,” this was unintentional. He added that he had treated employees with “kindness and respect” and was “deeply saddened” that his approach did not work for some lab members. Members of his lab have written to ETH leadership contesting the findings and complaining of “profound procedural flaws and biased reasoning” in the investigation.
Crowther shot to fame in 2019 with a headline-grabbing Science paper reporting that the planet had enough land for an extra trillion trees to be planted, and that doing so could sharply slow climate change. Some scientists criticized the conclusions as simplistic and suggested large-scale tree planting could damage grasslands. Crowther’s team issued corrections to the paper, and he clarified that he had never intended to encourage tree planting in open ecosystems.
That and other influential papers helped make Crowther “one of the most high-profile figures in global ecology,” says University College Cork ecologist Markus Eichhorn. His work gave rise to the World Economic Forum’s Trillion Trees initiative, and Crowther serves as a co-chair of the advisory board to the U.N. Decade on Ecosystem Restoration. But questions about his lab culture began to emerge. A September 2019 profile in Nature prompted a social media pile-on drawing parallels to the “toxic culture of Silicon Valley” and pointing out the lack of diversity in the lab. In a profile in Science 1 month later, Crowther responded that he was “seriously worried about” diversity and was making an effort to recruit more women. The gender balance in the lab has been at parity for the past 5 years, Crowther says.
In 2023 and 2024, complaints about Crowther’s behavior and financial compliance were filed with ETH, the new report says, prompting the university to engage a law firm to investigate. Some of the complaints were reported by Swiss newspaper Tages-Anzeiger last year, but it omitted details because of a court injunction prohibiting their publication. The court has partially lifted the injunction, and on Friday Tages-Anzeiger reported details of some complaints, including alleged unwanted approaches to women, which Crowther denies.
The report also says some employees describe a “toxic management culture” in the lab, with “sexist and discriminatory comments” and pressure to join social events. And it says lab members reported “repeated cases of inappropriate behavior towards employees in the context of pranks and games.”
The law firm investigated three specific allegations of “inappropriate personal advances,” all from past employees. The university concluded that contradictory accounts made the exact details difficult to establish, but that multiple current lab members corroborated the general problem of inappropriate behavior. Although many lab members enjoyed the highly social atmosphere in the lab, the report said, Crowther “displays a leadership style and general behaviour that at least partly contradicts ETH Zürich’s values.”
In an email to Science, Crowther’s lawyers wrote that he “welcomes the fact that … the allegations of harassment or other inappropriate behavior [have] been completely dropped.” The lawyers argue that “ETH has acknowledged between the lines that the complainants may not always have told the truth.” Crowther “never created a toxic culture and behaved appropriately towards all members of ETH,” the email says.
The university also found Crowther had broken various financial rules, including using ETH funds for public relations advice and legal fees after news of allegations against him broke in August 2024. The university said Crowther had attempted but failed to hire a family member. According to the report, the family member was then employed in another department while actually working for the Crowther lab. Crowther denies this, saying his sister helped his lab with social media posts in her spare time.
Lab manager Emily Clark disputes the claims about Crowther’s behavior, saying she never witnessed anything that “would be construed as personal misconduct or harassment.” The lab celebrated the diversity of its members and was a close-knit community, she says: “Tom has always been one of the most genuinely inclusive and accepting leaders I’ve ever worked with.”
Dozens of supportive posts on social media describe Crowther as “visionary and kind” and the Crowther lab as a “warm caring environment” with a “culture of inclusivity, respect, and unwavering support.” Postdoc Lidong Mo said on X that the lab was “the happiest and most supportive environment I have ever worked in.” In February, lab members //medium.com/@ian.brettell_51041/our-experience-our-voice-an-open-letter-from-members-of-the-crowther-lab-410a76a4c705" style="box-sizing: border-box; color: rgb(202, 32, 21); text-decoration: underline; background-color: transparent; word-break: break-word;">posted an open letter describing their positive experiences in the lab.
Sam Suarez, a former lab employee, welcomes the report, saying it provides “critical clarity” on the case. The university seems to have used the case as impetus to improve its safeguards, she says, but “time will tell” whether its efforts bear fruit.
Crowther would not comment to Science about his future or that of his ETH lab. “For now I am focusing on my mental health, and that of my lab members.” Clark says the lab is negotiating with the university to extend some members’ contracts, but that depending on the outcome, between 25 and 30 employees will lose their jobs, and in many cases will be forced to leave the country.
