America’s efforts to cut its climate change pollution stalled in 2024, with greenhouse gas emissions dropping just a fraction, 0.2 percent, compared to the year before, according to estimates published Thursday by the Rhodium Group, a research firm.

Despite continued rapid growth in solar and wind power, emissions levels stayed relatively flat last year because demand for electricity surged nationwide, which led to a spike in the amount of natural gas burned by power plants.

The fact that emissions didn’t decline much means the United States is even further off-track from hitting President Biden’s goal of slashing greenhouse gases 50 percent below 2005 levels by 2030. Scientists say all major economies would have to cut their emissions deeply this decade to keep global warming at relatively low levels.

Since 2005, United States emissions have fallen roughly 20 percent, a significant drop at a time when the economy has also expanded. But to meet its climate goals, U.S. emissions would need to decline nearly 10 times as fast each year as they’ve fallen over the past decade. That seems increasingly unlikely, experts say, especially since President-elect Donald J. Trump has promised to dismantle Mr. Biden’s climate policies and promote the production of fossil fuels, the burning of which generates greenhouse gases.

“On the one hand, it is notable that we’ve now seen two years in a row where the U.S. economy grew but emissions went down,” said Ben King, an associate director at the Rhodium Group. “But it’s far from enough to achieve our climate targets.”

The biggest reason that U.S. emissions have fallen in recent years is that electric utilities have been retiring their older, dirtier coal-fired power plants and replacing them with cheaper and less-polluting natural gas, wind and solar power. That trend mostly continued last year, with a few unexpected ups and downs.

The nation’s demand for electricity, which has stayed more or less flat for two decades, suddenly jumped by roughly 3 percent in 2024, in large part because scorching heat during the summer caused many Americans to crank up their air-conditioners. A smaller factor was that tech companies have been building more energy-hungry data centers in states like Virginia and Texas.

While power companies installed large numbers of wind turbines, solar panels and batteries last year to meet rising demand, natural gas use also rose to record highs, while coal use declined only slightly. The net result was that emissions from the power sector increased an estimated 0.2 percent, according to the Rhodium Group.

At the same time, transportation, the nation’s largest source of greenhouse gases, saw an 0.8 percent rise in emissions last year. Gasoline and jet fuel consumption both increased as Americans continued to drive and fly more after the pandemic. Nearly 10 percent of new car sales in 2024 were less-polluting electric vehicles, but those models still make up a small fraction of total cars on the road and have yet to put a major dent in transportation emissions.

On the flip side, emissions from America’s industrial sector — which includes steel, cement and chemicals — fell by 1.8 percent in 2024. Some of that may have been the result of lost output, as two hurricanes and a strike at the nation’s ports disrupted some factory activity in the fall, Mr. King said.

“It’s a reminder that there’s always some bumpiness in emissions,” Mr. King said. “It’s not just a question of how many electric vehicles are on the road or how much solar we’ve installed. A big portion of our economy still relies on fossil fuels.”

One of the most striking findings in this year’s data was that emissions from oil and gas operations dropped roughly 3.7 percent in 2024. Even though the United States produced record amounts of oil and near-record amounts of natural gas last year, many companies appear to have curbed leaks of methane, which is the main ingredient in natural gas and which can seep into the atmosphere and contribute significantly to global warming.

Over the past few years, the Biden administration and several states have adopted new regulations that require oil and gas producers to detect and fix methane leaks. Many companies also have financial incentives to capture methane to sell rather than vent it into the air.

Between 2014 and 2024, U.S. companies appear to have reduced the amount of methane that escaped, per each cubic feet of gas they produced, by 40 percent, according to the Rhodium Group.

Several experts have estimated that greenhouse gases generated in the United States could start dropping sharply in the years ahead if many clean energy policies stay in place, particularly the 2022 Inflation Reduction Act that pumped hundreds of billions of dollars into low-carbon energy technologies such as electric vehicles, wind turbines, solar panels, nuclear reactors, green hydrogen and batteries.

While Mr. Trump has pledged to scrap many of Mr. Biden’s subsidies and tax credits for electric vehicles and low-carbon energy, it remains to be seen whether Congress will agree.

That law has not yet had a major impact on the country’s emissions, said Mr. King, since it takes time for new factories to open and power plants to get built. But, he said, data shows that low-carbon energy and transportation now make up fully 5 percent of total U.S. private investment.

“That’s a leading indicator that things are changing quickly,” he said.

Mark Sutton, an Imperial College London paleontologist, is not a punk.

“I’m more of a folk and country person,” he said.

But when Dr. Sutton pieced together 3-D renderings of a tiny fossil mollusk, he was struck by the spikes that covered its wormlike body. “This is like a classic punk hairstyle, the way it’s sticking up,” he thought. He called the fossil “Punk.” Then he found a similar fossil with downward-tipped spines reminiscent of long, side-swept “emo” bangs. He nicknamed that specimen after the emotional alt-rock genre.

On Wednesday, Dr. Sutton and his colleagues published a paper in the journal Nature formally naming the creatures as the species Punk ferox and Emo vorticaudum. True to their names, these worm-mollusks are behind something of an upset (if not quite “anarchy in the U.K.”) over scientists’ understanding of the origins of one of the biggest groups of animals on Earth.

In terms of sheer number of species, mollusks are second only to arthropods (the group that contains insects, spiders and crustaceans). The better-known half of the mollusk family tree, conchiferans, contains animals like snails, clams and octopuses. “The other half is this weird and wacky group of spiny things,” Dr. Sutton said. Some animals in this branch, the aculiferans, resemble armored marine slugs, while others are “obscure, weird molluscan worms,” he said.

Punk and Emo, the forerunners of today’s worm-mollusks, lived on the dark seafloor amid gardens of sponges, nearly 200 million years before the first dinosaurs emerged on land. Today, their ancient seafloor is a fossil site at the border between England and Wales.

The site is littered with rounded rocky nodules that “look a bit like potatoes,” Dr. Sutton said. “And then you crack them open, and some of them have got these fossils inside. But the thing is, they don’t really look like much at first.”

While the nodules can preserve an entire animal’s body in 3-D, the cross-section that becomes visible when a nodule is cracked open can be difficult to interpret “because you’re not seeing the full anatomy,” Dr. Sutton said.

Paleontologists can use CT scans to see parts of fossils still hidden in rock, essentially taking thousands of X-rays of the fossil and then stitching those X-ray slices together into one digital 3-D image. But in these nodules, the fossilized creatures and the rock surrounding them are too similar in density to be easily differentiated by X-rays. Instead, Dr. Sutton essentially recreated this process of slicing and imaging by hand.

“We grind away a slice at a time, take a photo, repeat at 20-micron intervals or so, and basically destroy but digitize the fossil as we go,” Dr. Sutton said. At the end of the process, the original fossil nodule is “a sad-looking pile of dust,” but the thousands of images, when painstakingly digitally combined, provide a remarkable picture of the fossil animal.

Punk and Emo’s Hot Topic-worthy spikes set them apart from other fossils from the aculiferan branch of the mollusk family. “We don’t know much about aculiferans, and it’s unusual to find out we’ve suddenly got two,” Dr. Sutton said.

Stewart Edie, the curator of fossil bivalves at the Smithsonian National Museum of Natural History, said that Punk and Emo’s bizarre appearances shook up a long-held understanding of how mollusks evolved. Traditionally, scientists thought that the group of mollusks containing snails, clams and cephalopods “saw all of the evolutionary action,” said Dr. Edie, who was not involved with the new discovery. “And the other major group, the aculiferans, were considerably less adventurous.” But Punk and Emo “buck that trend,” he said.

The new alt-rock aculiferans reveal the hidden diversity of their group in the distant past and raise questions about why their descendants make up such a small part of the mollusk class today. “This is really giving us an almost unprecedented window into the sorts of things that were actually around when mollusks were getting going,” Dr. Sutton said. “It’s just this little weird, unexpected, really clear view of what was going on in the early history of one of the most important groups of animals.”