• Climate scientists acknowledged that it is hard to accurately quantify the exact size of the emissions and say the leaks are a "wee bubble in the ocean" compared to the massive amounts of methane emitted around the world every day.
• Nonetheless, environmental campaigners argue the incident reaffirms that the risk of sabotage or an accident makes fossil infrastructure a "ticking time bomb."
• Denmark's Energy Agency said emissions from the gas leaks correspond to about one-third of the country's annual greenhouse gas emissions.

Unexplained gas leaks along two underwater pipelines connecting Russia to Germany have sent huge volumes of methane, a potent greenhouse gas, into the atmosphere.

Climate scientists described the shocking images of gas spewing to the surface of the Baltic Sea this week as a "reckless release" of greenhouse gas emissions that, if deliberate, "amounts to an environmental crime."

Seismologists on Monday reported explosions in the vicinity of the unusual Nord Stream gas leaks, which are situated in international waters but inside Denmark's and Sweden's exclusive economic zones.

Denmark's armed forces said video footage showed the largest gas leak created a surface disturbance of roughly 1 kilometer (0.62 miles) in diameter, while the smallest leak caused a circle of approximately 200 meters.

Climate scientists acknowledge that it is hard to accurately quantify the exact size of the emissions and say the leaks are a "wee bubble in the ocean" compared to the massive amounts of methane emitted around the world every day.

Nonetheless, environmental campaigners argue that the incident shows the risk of sabotage or an accident makes fossil infrastructure a "ticking time bomb."

How bad is it?

Researchers at the German Environment Agency (UBA) estimate the climate impact of the leaks to be equivalent to roughly 7.5 million metric tons of carbon.

The agency said a total of 300,000 tons of methane are expected to be released into the atmosphere from the leaks. Methane is significantly more harmful to the climate than carbon, UBA researchers said, noting that over a 100-year period one ton of methane causes as much warming to the atmosphere as 25 tons of carbon.

For context, the International Energy Agency estimates that annual global methane emissions are around 570 million tons.

This means the estimated emissions from the Nord Stream gas leaks are just a fraction of the global total each year, even while campaigners argue the incident serves as another reminder of the risks associated with fossil fuel infrastructure.

Paul Balcombe, honorary lecturer in chemical engineering at Imperial College London, said that even if only one of the two leaking Nord Stream pipes were to release all its contents, it would likely be twice as much methane as the 2015 Aliso Canyon leak in California, the largest known release of methane in U.S. history.

Methane is 84 times more potent than carbon and doesn't last as long in the atmosphere before it breaks down. This makes it a critical target for combatting climate change quickly while simultaneously minimizing other greenhouse gas emissions.

The cause of the Nord Stream gas leaks is not yet known. Many in Europe suspect sabotage, particularly as the incident comes amid a bitter energy standoff between Brussels and Moscow. Russia has dismissed claims that it was behind the suspected attack as "stupid."

Denmark's Energy Agency said Wednesday that emissions from the gas leaks correspond to approximately one-third of the country's annual greenhouse gas emissions.

Based on the Danish government's initial estimates, the worst-case scenario would see 778 million standard cubic meters of gas or 14.6 million metric tons of carbon equivalent emissions. Comparatively, Danish emissions in 2020 were roughly 45 million tons of carbon equivalent.

Grant Allen, professor of atmospheric physics at the University of Manchester, said it has been estimated that there may be up to 177 million cubic meters of gas still residual in the Nord Stream 2 pipeline alone.

Allen said this amount is equivalent to the gas used by 124,000 U.K. homes in a year. "This is not a small amount of gas, and represents a reckless emission of greenhouse gases into the atmosphere," he added.

Jeffrey Kargel, senior scientist at Planetary Research Institute in Tucson, Arizona, described the gas leaks at the Nord Stream pipelines as a "real travesty" and "an environmental crime if it was deliberate."

"The massive roiling water due to the leak as we have seen in imagery is symbolic of the enormous amount of fossil fuel that the world is combusting," Kargel said.

"The global climate is changing drastically, with huge impacts on extreme climate mounting every year, decade after decade. It is such an extreme climate change that just about every adult age person on Earth knows it from first-hand experience," he added. "We can literally feel it on our skin."

Europe must go 'full tilt' for renewable energy

Neither pipeline was pumping gas at the time of the leaks but both lines were still pressurized: Nord Stream 1 stopped pumping gas to Europe "indefinitely" earlier this month, with Moscow's operator saying international sanctions on Russia prevented it from carrying out vital maintenance work.

The Nord Stream 2 pipeline, meanwhile, never officially opened as Germany refused to certify it for commercial operations due to Russia's unprovoked invasion of Ukraine.

Dave Reay, executive director of the Edinburgh Climate Change Institute, said "the most direct effect of these gas leaks on climate is the extra dollop of the powerful greenhouse gas methane – the main component of natural gas – they are adding to the atmosphere."

"That said, this is a wee bubble in the ocean compared to the huge amounts of so-called 'fugitive methane' that are emitted every day around the world due to things like fracking, coal mining and oil extraction," he added.

"Risks of sabotage or accident make fossil fuel infrastructure a ticking time bomb, but even on a good day oil and gas pipes and storage leak methane constantly," Silvia Pastorelli, EU climate and energy campaigner at environmental group Greenpeace, told CNBC via email.

"Behind all these numbers of cubic metres and megatonnes are real dangers for real people, this potent greenhouse gas is accelerating the climate crisis leading to worse heatwaves like Europe had this summer or more devastating like storms the one battering Florida now," Pastorelli said.

"Gas pipes from Norway or Algeria won't get us out of this mess, Europe must instead go full tilt for renewable energy and real energy savings that protect vulnerable people."