Update – 25 February 2016

A study published in the journal Science has quantified the scale of the spill even further, using 13 aircraft journeys and ground-level air samples to measure the leak.

It concludes that, in 112 days, the rupture at Aliso Canyon released 97,100 tonnes of methane — higher than the official California Air Resources Board estimate.

This is ten times larger than the blowout at Total’s Elgin rig in the North Sea in 2012.

It makes it the second largest methane leak recorded in the US, exceeded only by the collapse of an underground storage facility in Texas in 2004 — although the subsequent explosion and fire at this site meant that the methane was instantly turned into CO2, so the overall climate impact was less severe than Aliso Canyon.

While the well was leaking, it was the largest known source of human-caused methane emissions in the US, and effectively doubled the methane emission rate for the entire Los Angeles area.

Update – 19 February 2016

The Aliso Canyon gas leak was temporarily plugged on 11 February and permanently sealed on 18 February, putting a stop to the invisible plumes of methane that had billowed across the Porter Ranch area of Los Angeles since October 2015.

By this time it had spilled 94,000 tonnes of methane. This means that, in three and a half months, this one well released 0.4% of the total annual methane emissions of the entire US, and 0.04% of the annual US emissions for all greenhouse gases.

The Southern California Gas Company, which was behind the leak, is now battling criminal charges in court, after being accused of failing to report the damage at the storage facility. Its attorneys have pled not guilty.

 

In Los Angeles, an invisible environmental disaster is unfolding.

Since 23 October, natural gas has been leaking from a ruptured storage well in Aliso Canyon owned by the Southern California Gas Company (SoCalGas), spreading into the suburban neighbourhood of Porter Ranch.

The volumes of gas involved are enormous.

The most recent official estimate from California’s Air Resources Board (CARB) is that 66,000 tonnes of methane had spilled out from the well, as of 22 December (click here to view a zoomable version of the infographic).

A real-time counter maintained by the US-based campaign group Environmental Defense Fund estimates the total leakage on a second-by-second basis.

Many have suggested that the catastrophe is on the same scale as the 2010 BP oil spill.

But where Deepwater Horizon coated the Gulf of Mexico’s waters in black sludge, causing severe damage, the natural gas billowing from Aliso Canyon is invisible to the naked eye.

This video footage, shot using a specialised infrared camera on 17 December, is able to show the gas rising from the canyon’s underground storage well.

Part of the problem is the smell. While natural gas is not toxic, it is manufactured to have an odour so that leaks can be detected. This smell has caused a mass exodus from Porter Ranch, with residents complaining of headaches, nosebleeds and nausea.

The leak is also exacerbating the problem of climate change. The main component of natural gas is methane. This is a short-lived but potent greenhouse gas that has a warming effect 25 times higher than carbon dioxide (CO2) over a 100-year timeframe.

In January, California governor Jerry Brown declared a state of emergency in the Porter Ranch area of Los Angeles over the leak. David Clegern, a spokesperson for CARB, said that it was the largest natural gas leak ever to his knowledge.

“It is in California at this point the single largest source point of global warming,” he told the Guardian.

The scale of the problem

At the moment, it is difficult to know the full impact of the leak. Gas is still flowing continuously from Aliso Canyon, but at variable rates.

Measurements by CARB only capture the leakage rate at a particular moment in time. It has stressed that: “The emission rate of methane at the Aliso Canyon is not expected to be constant, as Southern California Gas continues to implement a range of strategies intended to stop the leak.”

This makes it impossible to know exactly how much gas has been released to date. With SoCalGas estimating a timeframe of late-February to late-March before the well is fixed, the drama looks likely to continue for several months yet.

Nonetheless, Carbon Brief asked several scientists to comment on the scale of the leak, based on events so far.

Jeff Peischl, a scientist affiliated to the US National Oceanic and Atmospheric Administration (NOAA), told Carbon Brief how the leak compared to the annual methane emissions from Los Angeles, California and the US as a whole, on the basis of Aliso Canyon continuing to leak at its current rate for an entire year. He says:

The current methane emission rate estimates released by the California Air Resources Board are approximately equal to the methane emissions from the entire Los Angeles urban area, and one quarter of the methane emissions from the entire state of California.

Peischl continues:

However, CO2 is still the dominant anthropogenic greenhouse gas emission, either globally, nationally, or in the state of California. As a result, this leak represents around 2% of the total anthropogenic greenhouse gas emission for the entire state of California. Nationally, the current methane emissions rate from the Aliso Canyon leak is approximately equal to 1-1.5% of U.S. anthropogenic methane emissions.

These numbers will be lower by a factor of two if the leak is fixed by March, he pointed out, and could also be lower if SoCalGas succeeds in decreasing the leak rate before it is fully stemmed.

Anthony Marchese, professor of mechanical engineering at Colorado State University, compared the scale of the Aliso Canyon leak to the volume of methane leaked from the US natural gas supply chain in total. He tells Carbon Brief:

The leak is estimated at 50,000 kilograms per hour (kg/hr). This is an extremely high leak rate for a single source. To put this into perspective, the total annual emissions from methane from the entire natural gas supply chain, as estimated in the 2014 EPA Greenhouse Gas Inventory, [converts into] a total US hourly emissions rate of 706,200 kg/hr. So, the single source at Aliso Canyon can be thought of as the equivalent of 7% of the total methane emissions from all US natural gas operations.

It is worth noting that the 50,000kg/hr was the leak rate recorded soon after the rupture. Averaging all measurements taken to date yields a leak rate of 43,550kg/hr, which puts the above percentage closer to 6%.

Robert Howarth, professor of ecology and environmental biology at Cornell University, also tells Carbon Brief that he and many other observers believe that the EPA figures for total US methane leaks from the natural gas industry underestimate the scale of the problem, which could mean the Aliso Canyon leak constitutes a lower proportion still.

Ilissa Ocko, a climate scientist at the Environmental Defense Fund, tells Carbon Brief:

For context on what this means for climate change, the amount leaked to date will have the same impact on warming over the next 20 years as burning over half a billion gallons of gasoline. Also, for context of scale, the amount leaking every day from Aliso Canyon alone during its peak is about the same amount leaking from the Barnett region in Texas that produces 7% of US natural gas and where 6 million people live.

Californian luck

The gas leak is just one more problem in the beleaguered state. California is currently in its fourth year of a record-breaking drought that led its governor to declare a state of emergency in 2014. Scientists say the likelihood of the drought was increased by climate change. The impact of this year’s El Niño has also started to hit the state, with storms increasing the chance of flooding and mudslides.

California is one of the most progressive states in the US, with regards to action on climate change. It aims to reduce emissions by 80% below 1990 levels by 2050, going well beyond federal targets. It has established a cap-and-trade market system to enable it to reach its goal.

California also has a 2020 goal to reduce greenhouse gas emissions back down to 1990 levels by 2020. The gas leak will make this harder to achieve, Peischl tells Carbon Brief:

California is attempting to reduce its 2013 greenhouse gas emissions by approximately 7-8% by the year 2020, so the Aliso Canyon leak represents around a quarter of this attempted emission reduction.

Ironically, the state is currently considering a new bill that would set methane reduction targets. Senator Ricardo Lara announced a proposal during the UN climate talks (COP21) in Paris last month to cut methane emissions by 40% by 2030, with legislation to be formally introduced in early 2016.

The Paris agreement set an aspirational goal of limiting global temperature rise to 1.5C under international law. This makes the Aliso Canyon leak, and methane reductions generally, even more urgent, considering the strong short-term impacts of the gas.

Howarth tells Carbon Brief:

If we are to meet the 1.5C of warming set by the COP21 last month, we absolutely must reduce methane immediately. So this is a big problem.

The reason for the leak — a removed safety valve — has thrown the topic of America’s ageing oil and gas infrastructure into sharp relief, and raised concerns that the Aliso Canyon leak could easily be repeated.

According to documents submitted by SoCalGas to regulators, the company has more than 50 storage wells that are over 70 years old. LA Weekly has reported that others may also lack safety valves.

The difference may be very slight, but when officials at the EPA come to plot US emissions for 2015/16, they will find their graph nudged upwards by the Aliso Canyon disaster. The gas billowing over Porter Ranch may be invisible, but the impacts will be as unmistakable as BP’s oil slick in the Gulf of Mexico in 2010.