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Nature Briefing: UV-Activated Tattoo Ink, PhD Pay Gaps and Climate Science at a Crossroads

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Invisible tattoo ink appears under UV light

Nanoscientists have developed a tattoo ink that becomes visible under ultraviolet light and can be hidden again using bright visible light. The ink contains small acrylic-glass spheres filled with photochrome, a compound that undergoes a reversible color change when exposed to certain wavelengths of light.

The technology could eventually be used in medical tattoos, including markers that help clinicians deliver radiation therapy to specific parts of the body.

Nature | 3-minute read

Reference: Matter and Light paper

Proposed US visa-training fee could threaten international science talent

US universities may soon have to pay higher fees when international students seek science jobs domestically after graduation. A proposal unveiled last week by President Donald Trump’s administration would require academic institutions to pay $100,000 for “optional on-the-job training”, allowing international students to work in the United States for up to three years after completing their studies.

Economist Michael Clemens says this and other measures designed to limit student immigration could “end up wiping out the pipeline” of scientific talent.

Nature | 6-minute read

IPCC deadlock could delay a major climate report

An unprecedented impasse among members of the Intergovernmental Panel on Climate Change (IPCC) could affect the publication of an influential climate-change report. The disagreement could leave the 2028 United Nations Climate Conference, COP33, without the latest scientific basis for its expected “global inventory” of progress.

Climate-change negotiations could proceed without the latest scientific basis. Climatologist and panel co-chair Robert Vautard said that the timeline for IPCC reports is typically approved within “minutes”. Oil-producing countries have been accused by other committee members of using the issue as a stalling tactic.

Reuters | 8-minute read

This week’s infographic: What do PhD students earn across Europe?

“It is notoriously difficult to collect comparative data on remuneration across Europe,” says Norbert Benze, one of the authors of a new report examining the earnings of first-year doctoral candidates in 26 countries during 2024–2025.

The report considers salary and tax structures, the cost of living and the prevalence of part-time contracts, particularly in Germany. Its findings suggest that large differences in doctoral pay could be contributing to a brain drain from parts of Europe to Scandinavia and the Benelux countries: Belgium, the Netherlands and Luxembourg.

Nature | 5-minute read

Reference: Report of the European Council of Doctoral Candidates and Young Researchers (Eurodoc)

Features and impressions

Can the Amazon rainforest absorb more carbon?

Step into the rainforest with climatologist David Lapolla, whose team is conducting large-scale climate research. The Amazon Free Air CO₂ Enrichment Experiment, or AmazonFACE, is scheduled to begin in the coming months and will run for 10 years.

The experiment will test predictions that rising atmospheric CO₂ could have a “fertilizing effect” on plants, encouraging growth and drawing more carbon from the air. That carbon could be stored in long-lived stem tissue—or it could move into leaves and then return to the soil, as happened in a similar experiment in a mature eucalyptus forest in Australia.

“If that were the case, the world wouldn’t get the kind of response it would expect,” Lapolla said.

Nature | 8-minute read

Why reading still matters in the smartphone age

In his book New Dark Age, journalist James Marriott argues that declining reading habits threaten people’s ability to think rationally and engage in coherent discussion.

Books, Marriott writes, make us “better, more knowledgeable people” and give us access to “the highest purposes and deepest solaces of human existence”. But smartphone distractions can erode the concentration needed for sustained reading. Science journalist David Adam described the book as “a love letter to the written word”.

Nature | 8-minute read

Why scientists are running AI models locally

Scientists are turning to tools such as Ollama and LM Studio to download large language models to their computers and chat offline. “I don’t want Claude to start telling people about my findings,” says neuroscientist Ian Gaudet.

Local AI tools allow researchers to query private PDF libraries and can improve reproducibility. Cloud-based AI providers may update their models without notice, meaning a query that works today could produce a different result next month.

Local models also have limitations, including the risk of “hallucinations” and the high cost of computers powerful enough to run them.

Nature | 11-minute read

Can you find the penguin?

On Friday, Leif Penguinson was drinking with a zebra (Equus quagga burchellii) Friends of Etosha National Park, Namibia. Did you find the penguin? When you’re ready, see the answer.

After one reader asked whether the zebra image could be an AI-generated clone, we want to clarify our approach. AI-generated images or text will never appear in a briefing without clear labelling and a good reason, such as an article about AI-generated images. If we discover that an image was generated by AI, as happened with the winner of the Small World in Motion Microscopy contest, we will let you know.

Our penguin-hunting puzzles are handcrafted each week by the briefing’s irreplaceable photo editor, Tom Houghton. Today is the Thanksgiving holiday in Flora Graham’s home country of Canada, making it the perfect opportunity to say: “Thank you, Tom!”

Thank you for reading,

Flora Graham, Nature Briefing Editor-in-Chief

Contributed by Jacob Smith

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