10 February 2026

Today’s Exemplar from Science Senior Editor Jesse Smith looks at the curious case of a methane surge. But first, catch up on the latest science news, including the underappreciated benefit of hosting a photosymbiont and a potential limit to the number of calories you can burn through exercise.

Ecology | Science

Persistent pesticides

It’s been more than 60 years since Rachel Carson’s Silent Spring woke the world to the dangers of pesticides. But have countries really stopped spraying them?

Clearly not, finds a new analysis published last week in Science . Researchers combined safety thresholds from seven international regulatory agencies to follow a single toxicity metric created by the United Nations (UN) called “total applied toxicity” (TAT). They then applied TAT to 625 pesticides, 65 countries, and eight ecological groups including fish, pollinators, terrestrial vertebrates, and even aquatic and terrestrial plants.

The metric revealed that global ecological toxicity increased during the study period of 2013 to 2019. Not all creatures suffered equally; toxicity rose 27% for fish and 43% for terrestrial arthropods, for example. Unsurprisingly, big agricultural powerhouses were big polluters: Brazil, India, Russia, and the United States contributed as much as two-thirds of the toxicity. Crops like fruits, vegetables, maize, soybean, rice, and cereals contributed up to 83% of global TAT.

The authors suggest that increased TAT is due to countries using larger volumes of pesticides, as well as more toxic ones in response to pests adapting to traditional chemicals. These trends directly counter the UN’s 2022 commitments to halve global pesticide use by 2030, note the authors. The study results “should be a stark warning that applied toxicities are still increasing in many regions, particularly for species groups that serve vital ecological functions,” lead author Jakob Wolfram told The Guardian.

Read the Paper

Evolution | Current Biology

Food friend or breathing buddy?

Tetrahymena thermophila Robinson/PLOS BIOLOGY (2006) via Wikimedia Commons | CC BY

In modern ecosystems, there are lots of organisms that host little photosynthetic pets inside them—the algae that live inside corals, for example—a phenomenon called photosymbiosis. It’s generally thought that these internalized photosynthesizers provide their hosts with food in exchange for protection and access to nutrients, so scientists have long assumed that supplemental carbon (i.e. food) for the host was the primary reason photosymbiosis evolved. However, a new study suggests that the first benefit of engulfing a photosynthesizer may have actually been extra oxygen—a by-product of photosynthesis—especially in the low-oxygen environments of early Earth.

Researchers studied Tetrahymena thermophila, a freshwater, single-celled protozoan covered in tiny hairlike cilia that it uses to swim and prey on microbes. In the lab, the team fed Tetrahymena different photosynthetic organisms, including algae and cyanobacteria; in some cases, the prey were not fully digested and continued to live inside the host.

Under normal conditions, these lingering organisms didn’t help much. The carbon they provided was of little benefit; sometimes the Tetrahymena grew slower, suggesting they were a hindrance. But when placed in well-lit, low-oxygen conditions, the photosynthetic cells of ingested organisms provided necessary oxygen, allowing the host to survive. In the dark, when photosynthesis stopped, the host protozoan died.

“We show that in an initial predatory-prey state, the supply of carbon by photosynthetic prey supports little growth of the predator, while the supply of oxygen in a hypoxic environment leads to a readily observable survival advantage,” the authors explained.

Read the Paper

pHYSIOLOGY | cURRENT bIOLOGY

There may be a limit to how many calories you can burn through exercise

It’s often assumed that losing weight is a matter of basic math. The human body burns a certain number of calories every day just by performing normal metabolic functions like breathing, circulating blood, and growing cells—no physical activity required. According to the predominant additive model, the number of calories a person burns during a workout simply gets added to that base number. But as new research shows, things may not be so straightforward.

A different model, known as the constrained total energy hypothesis, suggests that, when a person burns more calories through exercise, their body compensates by reducing the energy spent on tasks like cell repair and immune function. Some researchers have criticized this theory, and a study published in October of last year even appeared to debunk it . Now, in a new article, scientists reviewed 14 studies involving 450 people who participated in exercise programs, as well as several animal studies. They found that, while exercise does increase total energy use, the additive model tends to overestimate how many calories truly get burned. Some percentage—roughly 30% on average, the team reports—is offset through compensation, with the body finding ways to hang on to calories it would typically spend on other tasks.

This compensation, the team notes, tended to be greater for people who exercised while also eating a calorie-restricted diet, which “may help to explain why weight loss from exercise is typically modest, whether used alone or paired with diet.”

Read the paper

SPONSORED

Personalized CRISPR therapy delivered at record speed. Danaher helps turn bold ideas into faster breakthroughs in human health

SEE HOW

Exemplar

Because of fossil fuel emissions, methane steadily increased in the air in the 1980s until it reached an equilibrium when the rate of methane entering the atmosphere was similar to the rate of removal by oxidation. Atmospheric methane began to resurge in 2007, primarily because of emissions driven by wetlands, agriculture, and landfills. One part per billion (ppb) of atmospheric methane is equivalent to 2.8 million tonnes entering the atmosphere. M. HERSHER/SCIENCE

Ciais, P et al. Why methane surged in the atmosphere during the early 2020s. Science 391 (2025). 10.1126/science.adx8262

Solving the mystery of a methane surge

Jesse Smith, Senior Editor, Science

Methane is the second most important radiative forcing agent among all the anthropogenic trace greenhouse gases, with a climate warming effect second only to carbon dioxide. Therefore, it is important to understand why its atmospheric concentration changes. Its global atmospheric abundance is growing steadily but not monotonically, and the question of what factors are responsible for the variability the methane growth rate is a key one.

The long-term secular rise of atmospheric methane concentrations is, unsurprisingly, due largely to anthropogenic methane emissions from agriculture, the oil and gas industry, and waste management, which together contribute more than half of all global methane emissions. The shorter-term ups and downs that occur at a subdecadal timescale are more difficult to understand, though. Many factors have the potential to influence atmospheric methane concentrations, including changes in emissions from agriculture, wetlands, permafrost, wildfires and the oil and gas industry, which themselves depend on drivers such as climate change, rainfall changes caused by El Niño/La Niña, and economic factors, all of whose impacts can be difficult to attribute and untangle from each other.

The approach used by Ciais et al. is one way to try to do that . What the authors did was to look at the atmospheric methane record for the period since 2010, with particular attention on the latest wobble in a wobbly history: the puzzling surge that occurred after the beginning of 2019 and continued until the end of 2020. They concluded that the primary reason for the rapid increase in the growth rate was not what was going into the atmosphere but what was coming out. As is true for any given constituent of any dynamic reservoir, the atmospheric abundance of methane reflects the balance of input and output—the water level in a bathtub depends on how fast water is added from the faucet as well as how fast it is going down the drain.

In this case, they found that methane surged mostly because its consumption by hydroxyl radicals (OH) declined due to a drop in atmospheric OH concentration. OH is the primary atmospheric oxidant, responsible for the destruction of most organic air pollution like methane, so if its abundance decreases then its effectiveness as an atmospheric “detergent” also diminishes. Atmospheric OH concentrations are very difficult to measure directly, however, so the authors determined them using atmospheric chemistry models and determinations of the atmospheric abundances of key OH precursors, which (like methane) are easily measured, as well as by using estimates of the emissions of those precursors. Using that information, they showed that between 2020 and 2022, the concentration of atmospheric OH decreased enough to account for more than 80% of the methane concentration growth rate change, while emissions from wetlands and inland waters, plus contributions from agriculture and waste management, explained the balance.

The subsequent atmospheric methane decrease that occurred in 2022 and 2023 was due to the opposite combination: an increase in OH and a decrease in emissions. The authors also provide a good regional breakdown of the magnitudes and processes that caused these methane changes, and a model-grid-box-scale picture of methane emission anomalies for the different major sources. So, one study at a time, we are understanding what factors are driving variations in atmospheric methane concentration, and how to quantify them better.

Read the RELATED PERSPECTIVE

Read the paper

Et Cetera

Birds of different feathers flock together

Observations in Texas suggest that different bird species may preen each other often. “People think that nature is always about violence and conflict, red in tooth and claw,” said one expert. “But actually there’s a lot of collaboration and cooperation that goes on.”

Ecology and Evolution Paper | Read more at The New York Times

Not monkeying around

The board of directors of Oregon Health and Science University have voted to start discussions with the U.S. National Institutes of Health about transforming the Oregon National Primate Research Center into a reserve where no research is done. Some scientists are upset about the move. “It’s a travesty,” one former director of the facility said. “Why are we tearing down something that works very well? I’m shocked and disappointed.”