“It’s not trivial, but it’s a modest-sized U.S. city, something like that,” Drew Shindell, a professor of earth science at Duke University, said. “There are so many sources all around the world. Any single event tends to be small. I think this tends to fall in that category.”

New data released Wednesday by the Danish Energy Agency allowed scientists to produce preliminary estimates of the amount of methane released. If all that gas reaches the atmosphere, it would be equivalent to about 0.1 percent of the estimated annual global methane emissions, according to scientists with the U.S. Geological Survey’s Gas Hydrates Project.

From an emissions perspective, the breach is “an important one to watch,” said Carolyn Ruppel, chief of the project, who made the estimate with a colleague, Bill Waite. A worst-case calculation by Thomas Lauvaux, a researcher with the Laboratory of Climate and Environmental Sciences in France, equated it to what comes from about 1 million cars in a year — compared to the about 250 million cars operating in the E.U. alone.

E.U. warns of ‘robust’ response against sabotage after Nord Stream blasts

Other scientists cautioned against underestimating methane’s power. Paul Balcombe, a senior lecturer in chemical engineering and renewable energy at London’s Queen Mary University, called it a “really potent greenhouse gas” and that “even a little leak has quite a climate impact.”

Swedish monitoring stations that measure local atmospheric concentrations of greenhouse gases reported spikes since the pipeline burst, with methane concentration 20 to 25 percent higher than usual, “which is quite remarkable compared with our long-term data series,” Thomas Holst, a researcher at Lund University in Sweden, told The Post in an email, while maintaining it was not enough to pose a health risk.

Monitoring stations in Finland and Norway reported similar spikes. Ruppel noted that “methane is generally well-mixed in the atmosphere, so these local spikes would dissipate over the globe.”

Despite the size of the leak, it will not likely impact marine life in the way an oil leak might, Jasmin Cooper, a research associate at the Sustainable Gas Institute, said. “The environmental impact will be toward global warming.”

Images released Thursday by the Swedish Coast Guard still show a large mass of methane bubbles on the sea surface emanating from the four leaks across the pipelines — not three, as authorities initially said.

Scientists say that further imaging and access to the site are both necessary to get a clearer picture of the leaks and to calculate how much methane might be released into the atmosphere.

“We know it’s leaking badly because we see the pictures and video of the gas bubbling at the water surface, but we don’t know anything about the leaks,” Cooper said. “We don’t know how big they are or where they are in the pipeline, and so it’s difficult to figure out the flow rate.”

Danish officials said Wednesday that they anticipate both pipelines being empty by Sunday, as more than half of the gas had already been released. Once the gas is gone, they said, scientists and security officials will have better access to the site, which has been limited because of safety concerns.

The dissipation of the gas will also allow forensic experts to examine the site for clues at what caused the explosion, which has fixated security officials across Europe.

NATO issued its strongest statement yet on Thursday over the breaches in the Nord Stream pipelines in the Baltic Sea, describing the damage as the result of “deliberate, reckless, and irresponsible acts of sabotage.”

An E.U. official reiterated Thursday that the damage to the pipelines was “not a coincidence.”

The Swedish National Seismic Network put the strength of the larger second blast at equivalent to 100 to 200 kilograms (220 to 440 pounds) of TNT. The first was smaller and consequently harder to measure.

Arms experts say it is difficult to guess what kind of munition might have caused the damage. It is possible that a torpedo was used, but more likely that divers or an autonomous underwater vehicle put one or more demolition charges on each site. To identify the weapon or weapons used, more evidence — including additional sensor data, as well as physical evidence such as munition remnants — would be required.

With the consensus among European leaders that sabotage was involved, suspicion is increasingly falling on Russia, which has used energy supplies as leverage against Europe since the invasion of Ukraine.

Intelligence officials have begun poring over communications intercepts, sonar signatures and other records that might reveal suspicious activity in the weeks or months leading up to the explosions. Two senior officials with two European security services said Russia remains a main suspect because it has the technical means to carry out subsurface attacks on key infrastructure and has demonstrated its determination to destabilize energy markets in Europe.

The officials, which spoke on the condition of anonymity because of the sensitivity of the subject, emphasized that these are preliminary, analytic conclusions with no evidence emerging so far to implicate Moscow.

The Kremlin has denied responsibility for the incident, suggesting Thursday that the incidents should be investigated as “an act of terrorism” and a coordinated international investigation is required, as Russia is the majority owner of both pipelines.

Maria Zakharova, the spokeswoman for the Foreign Ministry, has also hinted that the United States could be behind the blasts.

“The absolute beneficiary of this situation was Washington,” she said Thursday. “Mr. Blinken, made no secret of the fact that the main goal was to cut Europe off from Russian energy resources, and now you don’t know who might benefit from it. It benefits you!” she added addressing the U.S. secretary of state.

A U.S. official, also speaking on the condition of anonymity to discuss a sensitive matter, said Wednesday the United States had nothing to do with the attack on the Nord Stream pipelines, calling the idea “preposterous.”

Francis reported from London. Greg Miller in Washington, Emily Rauhala in Brussels, Martin Selsoe Sorensen in Copenhagen, Natalia Abbakumova in Riga, Latvia, contributed to this report.