The biggest science stories that lit up our world in 2024

As nearly half of the world’s population headed to the polls this year, politics grabbed many of the headlines. But scientists and the natural world also managed to attract the public’s attention. Here, Knowable Magazine takes a look at some of the most notable research-related events and discoveries of 2024, as well as a few studies and policy moves that we are eager to watch play out in the coming year.

Sky show

Celestial events encouraged many people to look skyward this year, with the Sun taking center stage.

In April, millions of people stopped to watch the “Great North American Eclipse.” Total solar eclipses happen every year or two, but this one provided the longest period of totality visible from land in over a decade, casting its shadow on a path smack over North America. The show was mostly of interest as a public spectacle, but citizen science projects also helped to collect data that should, for example, help to refine models of solar activity.

WATCH: Millions of people witness rare total solar eclipse across North America

Sky gazers were also stunned by auroras this year, thanks to a natural peak in solar activity caused by the 11-year cycle of the flipping of the Sun’s magnetic poles. While this solar maximum doesn’t look particularly strong in terms of the number of sunspots, “there were many more big flares than we would expect compared to the last cycle,” says solar physicist Lyndsay Fletcher of the University of Glasgow. “It’s quite exciting.” Big flares in May created the biggest solar storm to reach the Earth in just over two decades, and more big flares brought bright lights to the skies in October.

The last dramatic year for auroras was two cycles ago, in 2003. Back then, we didn’t have pervasive cell phone cameras that could easily capture aurora colors, or social media sites like Facebook to spread the news. The show will continue: Forecasts show the solar maximum lasting into early 2025.

READ MORE: Wondering why the aurora borealis was visible so far south? Here’s why it’s all thanks to the sun

Alongside these solar fireworks, heliophysicists have some fresh data to look forward to: This Christmas Eve, NASA’s Parker Solar Probe mission will get closer to the Sun than ever before, zooming by at 3.8 million miles from the surface. Such studies help astronomers to better understand the solar activity that leads to both auroras and space weather that can foul up electrical equipment.

Total map of a brain

In October, scientists published the first complete map of a complex (though tiny) brain: that of the fruit fly Drosophila melanogaster, one of the most-studied animals in biological research. The new “connectome” charts the wiring between 140,000 neurons, giving new insights into the roles of different brain regions.

The human brain presents a far bigger challenge, with more than 80 billion neurons. But scientists have made a start. In May, researchers at Google revealed a 3D image of a tiny piece of human brain the size of half a grain of rice, containing about 16,000 neurons. That adds to a high-resolution atlas of brain architecture created by the European Union’s Human Brain Project last year.

Artificial intelligence (AI) algorithms are helping to tackle these data-heavy tasks. Along with seeking to better understand fundamentals of how the brain works, such projects aim to solve mysteries of human mental illnesses or chart better paths to recovery after brain injury — and, along the way, might also help to improve AI.

Hot Earth

It will come as no surprise that 2024 once again broke heat records, with the global average temperature topping 1.5 degrees Celsius above the pre-industrial average for the first time. High summer temperatures brought the planet’s fourth and most widespread global coral bleaching event, affecting around 75 percent of global corals.

WATCH: How Climate Corps members are tackling the climate crisis in communities across the U.S.

A warmer planet comes with extreme weather: Unusual heat in the Gulf of Mexico fed supercharged hurricanes, and Valencia, Spain, received more than a year’s worth of rain in eight hours in October, causing deadly flooding. “The urgency is very tangible,” says Andrew Satchwell, an energy economist at Lawrence Berkeley National Laboratory who works on climate policy.

A pedestrian crosses a street in downtown Los Angeles on Sept. 4, 2024, as Southern California faces a heat wave. Photo by Etienne Laurent/ AFP via Getty Images

Global carbon dioxide emissions looked like they were starting to level off in 2023, but 2024 saw emissions bump upward again. The world is not on track to hit Paris Agreement targets that aim to limit warming. Instead, current policies and actions look set to see a world that’s perhaps 2.7 degrees C warmer by 2100. Still, a few policy moves are starting to see traction. In the United States, for example, substantial pots of cash from the Inflation Reduction Act to decarbonize the country’s energy started to flow in 2024. “I think we have seen a turn,” says Satchwell.

Efforts to track emissions of methane — an even more powerful though shorter-lived greenhouse gas — have revealed some nasty surprises. The largest inventory of methane emissions from U.S. oil and gas production, for example, found them to be around three times the government estimate. A 2024 report highlighted a worrying bump up in large methane leaks detected, including a record-breaking blowout in Kazakhstan that lasted more than 6 months.

Dealing with dementia

This year, several researcher groups took big steps toward a simple and cheap blood test for Alzheimer’s disease, which accounts for around two-thirds of the world’s 55 million cases of dementia; the UK’s Blood Biomarker Challenge hopes to add a routine blood test for dementia to the British public health care system within five years.

More extensive diagnosis is key to tackling Alzheimer’s, says Joshua Grill, director of the Institute for Memory Impairments and Neurological Disorders at the University of California, Irvine. “We have to catch people early.”

READ MORE: FDA approves 2nd Alzheimer’s drug that can modestly slow dementia

The disease has no cure, but early-stage patients may benefit from new drugs that aim to slow its progression: Monoclonal antibodies that target amyloid protein, which builds up in the brains of Alzheimer’s patients, have made waves after a 20-year gap with no new drugs for the disease. “These positive trials were a big deal and very welcome,” says Grill. Donanemab was approved in the United States this year, following lecanemab’s approval in 2023.

Such drugs might even prove effective at preventing the disease in high-risk people who haven’t yet shown memory symptoms; trials are underway and the results should be out in four years, says Grill. Meanwhile, a 2024 Lancet report by a panel of dementia experts listed more than a dozen simple actions that research has shown can help to prevent or delay dementia, from using hearing aids to keeping cholesterol in check and exercising.

Work on conditions that plague our later years is welcome as the global population ages dramatically. Between 2015 and 2050, the percentage of people over 60 years old is expected to nearly double, to 22 percent.

Plastic pollution panic

Children walk on a garbage dump filled with plastics in Rodriguez, Rizal province, Philippines, on Nov. 28, 2024. Photo by Eloisa Lopez/ Reuters

Plastics hit the spotlight this year as delegates to the United Nations tried to thrash out an international treaty to end plastic pollution. Although they failed to come to an agreement by December as originally planned, their work will continue next year.

READ MORE: Negotiators fail to reach agreement on plastic pollution treaty at talks in South Korea

There are now an estimated eight gigatons of accumulated plastic on Earth — twice as much as the weight of all animal life. Plastic has leached into every corner of our lives, including our oceans, air, food, blood and mothers’ milk. To support the treaty process, researchers modeled various plastic control policies and cataloged more than 16,000 plastic chemicals. More than 4,200 of these were found to be of concern because they were “persistent, bioaccumulative, mobile and/or toxic.”

“I would far rather we take the time needed to agree upon a strong treaty rather than settle for something of little substance,” says Richard Thompson, a marine biologist at the University of Plymouth in England who studies plastics and is coleader of the Scientists’ Coalition for an Effective Plastics Treaty. “Personally, I remain hopeful; there are answers to this problem.” The key, he says, is to dramatically reduce overall production, and make the remaining essential plastics “better by design” — with more recycled content, for example, and fewer toxic additives.

Researchers also continue to seek out better ways to recycle or dispose of plastics (including finding fungi or bacteria to do the job), or to create more biodegradable versions.

AI gets supercharged

Artificial intelligence programs improved dramatically this year. The large language models that power chatbots like ChatGPT have now surpassed people in many areas; some can achieve medal-worthy performance in the Math Olympiad and beat science PhDs in “Google-proof” tests of their own fields. The wave of developments caught the eye of the Nobel committee, with 2024 prizes in both physics and chemistry going to AI-related discoveries.

As the technology advances, the electricity and water demand for the computing that powers AI has ballooned worryingly. “We’re starting to see industrial-scale challenges for power supply,” says data scientist Jakub Kraus from the Center for AI Policy in Washington, DC, who notes that big tech companies are now turning to nuclear power to fill their voracious energy needs.

Despite their cleverness, chatbots continue to make serious mistakes, hallucinate false facts and perpetuate bias. Misuse can cause serious problems. AI-generated deepfakes made waves in this year’s elections, for example when Joe Biden’s voice was cloned to send out fake telemarketing calls urging Democrats not to vote in the primaries.

The European Union’s AI Act, which went into force in August, will begin to regulate AI providers and ensure good practices, such as transparency about how the systems work. “This is a good step forward,” says Kraus. “Overall, there has not been a major AI policy package in the US. That might change.”

Votes cast for change

2024 was a year of both communal action and global divides. Around the world, a record-setting number of voters headed to the polls: More than 75 nations, holding roughly half of the world’s population, held national elections. The prevailing trend was for change: An ABC News analysis showed that in over 80 percent of democracies, the incumbent party lost seats or voter share.

SERIES: America at a Crossroads

In this banner “super year” for elections, the entire concept of democracy is facing challenges. Voter turnout is going down, riots have become more common, election results are often disputed in courts and there are deep and troubling social divides, including in the United States.

“American democracy is in crisis,” writes legal scholar Bertrall Ross of the University of Virginia in the 2024 Annual Review of Law and Social Science. “Both sides perceive every election as an existential threat to their ways of life.”

A river runs through it

Athletes dive into the Seine river to start the swimming stage of the men’s individual triathlon at the Paris 2024 Olympic Games in Paris on July 31, 2024. Photo by Anne-Christine Poujoulat/ AFP via Getty Images

The Paris Summer Olympics threw a spotlight on water pollution when athletes complained bitterly about the poor condition of the Seine, which was meant to be clean for the games. Paris is not alone. Rivers the world over increasingly face troubles from pollution, decreased water supply and more. An August series of reports from the UN Environment Program found worrying changes to the distribution, quantity and quality of river water globally: River flow, for example, has decreased in 402 basins worldwide.

That may be a small fraction of the total 12,572 basins, but it’s a fivefold increase over the number of dwindling rivers documented 15 years ago. And pollution makes things worse. A 2024 research paper concluded that out of 10,000 global river basins, around 1,000 face problems because of water scarcity, and that number more than doubles, to 2,500, when taking into account nitrogen pollution, mainly from agricultural runoff.

Disease dangers spreading

The mosquito-spread dengue virus raised alarms this year as cases hit record numbers. The Americas have been hardest hit, with more than 12 million cases — double the number from 2023 and three to four times the average over the past five years.

READ MORE: What you need to know about the latest outbreak of dengue fever

In October, the World Health Organization launched a plan to tackle the disease globally. Dengue is rarely fatal, says Scott Weaver, director of the Institute for Human Infections and Immunity at the University of Texas Medical Branch in Galveston. But the meteoric rise in cases has infectious disease specialists scratching their heads. “I’m worried that we don’t understand what’s going on,” Weaver says. Climate change might be part of the answer. Other mosquito-borne diseases like West Nile virus are on the rise in more temperate climes like Europe as the world warms.

A worker fumigates against mosquitoes around a building after a spike in dengue fever cases in Penuelas, Puerto Rico, on March 27, 2024. Photo by Ricardo Ortiz/ Reuters

Meanwhile, mpox is also a pressing concern. The disease — previously known as monkey pox — was considered a disease largely spread to humans from other animals and endemic to central and west Africa. Then in 2022, cases spread by close person-to-person contact began popping up globally. In August 2024, an outbreak in the Democratic Republic of the Congo was declared a public health emergency of international concern as a more virulent and deadly form of the virus — called clade 1 — started to spread, with the first known case appearing in the U.S. in November. “This is pretty concerning,” says Weaver.

Five years after the outbreak of COVID-19, better plans for coping with pandemics remain elusive: Delegates to the World Health Organization disappointingly failed to come to an agreement for a treaty on pandemic responses this year. “I’m not very optimistic that international cooperation is going to improve a lot,” says Weaver.

Moon matters

Several craft are sent to the Moon every year, but 2024 brought a few special successes: Texas-based Intuitive Machines became the first company to put a lander on the Moon, and Japan became the fifth nation to do so. Excitingly, China’s Chang’e-6 mission brought back the first rocks ever collected from the “far side” of the Moon, with signs of surprisingly young volcanism.

READ MORE: Catch the supermoon lunar eclipse? Here’s what you saw

“After the Apollo missions, it was thought that the Moon was homogenous, and there was a feeling we’d ‘been there done that.’ We now know that’s not true; it’s much more rich and varied,” says planetary geologist John Spray of the University of New Brunswick in Canada. “There’s renewed excitement about what we can learn from the Moon.” NASA is planning to send people back to explore, starting with an orbital mission in 2025.

Aliens ahoy

There’s no proof of alien life as yet, but researchers keep looking. In July, NASA’s Perseverance rover took photos of an intriguing rock on Mars with leopard-pattern spots that could be evidence of ancient microbes. “These spots are a big surprise,” said David Flannery, an astrobiologist on the Perseverance science team, in a statement from NASA. “On Earth, these types of features in rocks are often associated with the fossilized record of microbes living in the subsurface.”

In May, astronomers spotted a planet, Gliese 12 b, that’s only slightly larger and warmer than Earth and could be habitable — one of a handful of Earth-like worlds among the more than 5,000 exoplanets spotted over the past 30 years, and among the closest such finds to date at just 40 light-years away.

READ MORE: Pentagon study finds no sign of alien life in reported UFO sightings going back decades

Aliens may be top of mind for those captivated earlier this year by Netflix’s mind-bending 2024 sci-fi hit “3 Body Problem,” about an alien civilization threatened by chaotic climate caused by unpredictable orbits of its three suns. The story is kicked off by a real-life event: a mysterious radio signal picked up in 1977 that is often conjectured to be a sign of intelligent communication. Sadly, this August the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo published a report proposing a natural origin for the so-called WOW! signal: the sudden brightening of a cold hydrogen cloud.

The show’s 3 Body Problem, by the way, is also a real-life puzzle in physics: how to predict the interaction of three large objects like stars in which none dominates the orbits of the others. Mathematicians made progress this year in finding a less computationally intensive way of calculating the outcomes of these chaotic systems.

This story first appeared in Knowable Magazine.